forest atmosphere carbon transfer and storage (facts-ii). the
TRANSCRIPT
Forest Atmosphere Carbon Transfer and Storage
(FACTS-II) The Aspen Free-air CO2 and O3
Enrichment (FACE) Project: An Overview
R.E. Dickson, K.F. Lewin, J.G. Isebrands, M.D. Coleman,
W.E. Heilman, D.E. Riemenschneider, J. Sober, G.E. Host,
D.R. Zak, G.R. Hendrey, K.S. Pregitzer, and D.F. Karnosky
The use of trade, firm, or corporation names in this publica-tion is for the information and convenience of the reader.Such use does not constitute an official endorsement orapproval by the U.S. Department of Agriculture or the ForestService of any product or service to the exclusion of othersthat may be suitable.
Table of Contents
PageI. Executive Summary ............................................................................................................ 1
II. Introduction ........................................................................................................................ 3A. Atmospheric Carbon Dioxide ...................................................................................... 3B. Carbon Dioxide Effects on Plants ................................................................................ 3C. Atmospheric Ozone ..................................................................................................... 7D. Ozone Effects on Plants .............................................................................................. 9E. Carbon Dioxide and Ozone Interactions .................................................................... 11F. The Importance of FACE Systems ............................................................................. 11G. Unique Characteristics of the Aspen FACE Project at Rhinelander ............................ 12H. Multidisciplinary Approach ....................................................................................... 12I. Aspen: Genetic Variation and Economic Importance ................................................. 13
III. Goals and Objectives ......................................................................................................... 13
IV. Experimental Methods ...................................................................................................... 14A. Site Description ........................................................................................................ 14B. Study Design ............................................................................................................ 15C. Plant Material, Propagation, and Planting ................................................................. 17D. Site Safety ................................................................................................................ 20E. Micrometeorological Monitoring ................................................................................ 21F. Experimental Variables Measured ............................................................................. 25
V. Carbon Dioxide/Ozone Delivery and Control System ......................................................... 27A. Carbon Dioxide Supply System ................................................................................. 27B. Ozone Supply System ............................................................................................... 29C. Fan and Plenum ....................................................................................................... 29D. Vertical Vent Pipes .................................................................................................... 29E. Gas Enrichment Control System ............................................................................... 33
VI. Funding Partners, Research Cooperation, and Research Approach .................................... 42
VII. Database Management ...................................................................................................... 43A. Site Data ................................................................................................................. 44B. Meteorological Data Collection and Processing ......................................................... 44C. Operational Performance Data ................................................................................. 45D. Biological Data......................................................................................................... 45
VIII. Process Modeling at the Aspen FACE Site .......................................................................... 45
IX. Statistical Considerations and Data Analysis .................................................................... 47
X. Literature Cited ................................................................................................................. 49
XI. Acknowledgments ............................................................................................................. 56
XII. Appendices ....................................................................................................................... 57
List of Tables
Table 1.—Summary of soil properties for the Aspen FACE site for 1997Table 2.—Aspen FACE meteorological monitoring (rings)Table 3.—Aspen FACE meteorological monitoring (ambient tower)Table 4.—Experimental variables measured in the Aspen FACE ProjectTable 5.—Carbon dioxide concentration control performance by month in 1998 for the Aspen
FACE ProjectTable 6.—Ozone concentration control performance by month in 1998 for the Aspen FACE ProjectTable 7.—Monthly average ozone concentration and Sum O for the Aspen FACE Project during the
1998 exposure seasonTable 8.—Maximum daily and hourly mean ozone concentration for each month of the 1999 expo-
sure seasonTable 9.—Sample data analysis of chlorophyll meter (SPAD) observations made on several trees of
each clone within the aspen subplotsTable A1.—Relationships between soil matric potential and gravimetric water content for the Aspen
FACE siteTable A2.—Detailed soil properties for the Aspen FACE site for 1997Table A3.—Diurnal ozone concentrations for ring 1,4 of the Aspen FACE site for June 1999
List of Figures
Figure 1.—Atmospheric CO2 concentrations and global temperaturesFigure 2.—Atmospheric CO2 concentration change during the past 150 yearsFigure 3.—Average global temperature change during the past 100 yearsFigure 4.—Distribution of O3 over Eastern North AmericaFigure 5.—Increasing O3 concentrations in the troposphere during the 20th centuryFigure 6.—Aspen FACE Project, Harshaw Experimental Farm, Rhinelander, WisconsinFigure 7.—Aspen FACE Project, location of the individual treatment rings and facilities within the
32-ha siteFigure 8.—An individual treatment ring tree mapFigure 9.—An individual treatment ring micrometeorological and equipment mapFigure 10.—Aspen FACE meteorological instrument towerFigure 11.—Central control systems for CO2, liquid O2, O3 production, and gas distributionFigure 12.—Individual treatment ring configurationFigure 13.—Individual treatment ring gas distribution equipmentFigure 14.—Comparison of fenceline and regional ambient O3 concentrations with daily O3 treat-
ment concentrations for July 1998Figure 15.—Isolines of CO2 concentrations within the multiport-equipped CO2 treatment ringFigure 16.—Funding partners, research partners, and research approach of the Aspen FACE
ProjectFigure 17.—Database management organizational structure for the Aspen FACE ProjectFigure 18.—Primary data flow-diagram and modeling framework of database management for the
Aspen FACE ProjectFigure 19.—The WIMOVAC model schematic showing main sub-model componentsFigure A1.—Aspen FACE site layout—RoadsFigure A2.—Aspen FACE site layout—Meteorological stationsFigure A3.—Aspen FACE site layout—Carbon dioxide supply linesFigure A4.—Aspen FACE site layout—Oxygen, ozone supply linesFigure A5.—Aspen FACE site layout—Fiber optic cableFigure A6.—Aspen FACE site layout—Underground electrical cableFigure A7.—Aspen FACE site layout—Irrigation lines
I. EXECUTIVE SUMMARY
Human activities have modified regional envi-ronments for thousands of years. These activi-ties are now increasing at such a rate and oversuch large areas that there is genuine concernthat not only regional environments, but alsothe global environment will be affected. TheIntergovernmental Panel on Climate Change(IPCC) has concluded that over the past 150years, significant climate change has takenplace and that human activities have signifi-cantly contributed to these changes. Indicatorsof past atmospheric conditions and climatechange found in Greenland and Antarctic icecores and in deep sea sediments show that forthe past 160,000 years, global temperaturesand the concentrations of atmospheric green-house gases were closely correlated. Duringthis long period, atmospheric carbon dioxideconcentrations rarely exceeded 300 µll-1 andcommonly ranged between 180 and 250 µll-1.Since the middle of the 19th century, however,atmospheric carbon dioxide (CO2) concentra-tions have increased from about 280 µll-1 to the
current 360 µll-1, largely from burning fossilfuels (coal, oil, gas) and from burning andconverting forests to grasslands and croplands.Average global temperature has also increasedby about 0.5oC. At the current rate of increase,concentrations of atmospheric CO2 and othergreenhouse gases are expected to double in thenext 100 to 150 years, and global temperaturesare expected to increase by 1o to 4oC. Regionalresponses may be even greater. In addition,there may be significant changes in agricul-tural and natural ecosystem productivity,biogeochemical cycling, and availability ofwater resources, as well as increases inweather extremes, shifts in plant hardinesszones, and a rise in sea level. Such changes inregional and global climate could have severeimpacts on world economies and public health.
Forest and woodland ecosystems contain amajor portion of the world’s biomass and aresignificant contributors to biosphere-atmo-sphere CO2 cycling and carbon storage. Infor-mation on forest responses to different factorsassociated with climate change will be critical
Forest Atmosphere Carbon Transfer and Storage(FACTS-II) The Aspen Free-air CO2 and O3
Enrichment (FACE) Project: An Overview
R.E. Dickson1, K.F. Lewin2, J.G. Isebrands1, M.D. Coleman3, W.E. Heilman4,D.E. Riemenschneider1, J. Sober6, G.E. Host5, D.R. Zak6, G.R. Hendrey2,
K.S. Pregitzer7, and D.F. Karnosky7
1 USDA Forest Service, North Central Re-search Station, Forestry Sciences Laboratory,5985 Highway K, Rhinelander, WI 54501.
2 US DOE, Brookhaven National Laboratory,Department of Applied Sciences, Division ofEnvironmental Biology and Instrumentation,P.O. Box 5000, Building 318, 1 S. TechnologySt., Upton, NY 11973-5000.
3 USDA Forest Service, Savannah RiverInstitute, P.O. Box 700 Building 760-15G, NewEllington, SC 29809.
4 USDA Forest Service, North Central Re-search Station, Forestry Sciences Laboratory,
1407 South Harrison Road, East Lansing, MI48823.
5 Natural Resources Research Institute, 5013Miller Trunk Highway, Duluth, MN 55811.
6 University of Michigan, School of NaturalResources and Environment, 430 E. University,Room 2534 Dana Building, Ann Arbor, MI48109.
7 Michigan Technological University, Schoolof Forestry and Wood Products, 1400 TownsendDrive, Houghton, MI 49931.
for fine-tuning global climate change scenariosand modeling efforts. Of particular importanceis tree response to tropospheric CO2 and ozone(O3), both of which are increasing in concentra-tion and will continue to do so well into thefuture. Increasing atmospheric CO2 concentra-tions have the potential to increase forestproductivity because photosynthetic rates arelimited by current CO2 concentrations. Incontrast, O3 is a phytotoxic gas that is reactiveat very low concentrations. Current ambientO3 concentrations over large portions of theEastern United States may already be decreas-ing growth and productivity of O3-sensitive treespecies. Because elevated CO2 exposure mayincrease photosynthetic rates and resistance toother environmental stresses, it is generallybelieved that increasing atmospheric CO2
concentrations will offset the detrimentaleffects of increasing O3 concentrations. How-ever, results of recent studies on the interactingeffects of CO2 and O3 are contradictory; someshow amelioration, others show no effect ofincreased CO2 or even an increase in the O3
response.
There is a huge amount of research informa-tion about the response of plants to increasedCO2 concentrations and increased O3 concen-trations, but relatively little information aboutCO2 and O3 interactions. Most of this informa-tion comes from studies on plants in green-houses, growth chambers, or field enclosures.Chamber effects are always present in thesesystems, and the size of these systems usuallyrequire experiments with potted seedlings orsmall plants. Pots restrict root growth, andseedling response may differ from that of largetrees. Long-term studies (3 to 4 years) of largerplants in open-top chambers more closelyapproximate natural conditions, but chambereffects are still present. Because of theselimitations, results from extrapolating chamberresponses of seedlings to large trees in foreststands are questionable.
The need for large-scale field experiments toevaluate the response of plants growing in theopen under natural conditions has been recog-nized for some time. However, the technologyto control the concentration of CO2 and othertrace atmospheric gases throughout large areasof big plants has only recently been developed.Free-Air Carbon dioxide Enrichment (FACE)systems provide the experimental means to
control CO2 concentrations over large areas (upto 30-m-diameter circles) without appreciablechanges in other environmental factors. Withinthe last 10 years, FACE systems have beendeveloped for agricultural crops, tall-grassprairie, desert scrub and grasses, southernpines, southern hardwoods, and northernhardwoods. The overall goal is to study theresponse of widely different ecosystems toelevated CO2 and other trace gases and tominimize duplication of effort with these largeand expensive experimental systems. FACEsystems, although expensive to install andoperate, provide economies of scale such thatcosts per unit of ground area or of experimentalplant material are significantly lower thanthose of other enrichment systems, such asopen-top chambers. In addition, the largeexperimental area and large amount of plantmaterial provide opportunities for cooperationamong investigators with widely differentexpertise and for studies that range in scalefrom cellular to ecosystem processes. OurAspen FACE project at Rhinelander, Wisconsin,is unique because of its large size (twelve 30-mdiameter rings), the combination of both CO2
and O3 exposures, exposure of the plant mate-rial to elevated CO2 and O3 from the seedlingstage to maturity, and the inclusion of threetree species (trembling aspen, paper birch, andsugar maple) and five aspen clones known todiffer in response to CO2 and O3.
This publication:• Briefly reviews the rationale for studying
the response of forest stands to increas-ing concentrations of CO2 and O3;
• Describes the development of FACTS-II,the Aspen FACE project;
• Outlines the experimental variablescurrently being measured;
• Credits our research and funding part-ners;
• Describes the CO2 and O3 delivery andcontrol systems; and
• Examines some of the database manage-ment and statistical considerationsinvolved.
We hope that this publication will be the pri-mary reference source for the Aspen FACEProject and that it will be useful for all ourresearch partners in publishing their individualresearch results.
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II. INTRODUCTION
A. Atmospheric Carbon Dioxide
Changes in atmospheric chemistry and thepotential changes in global climate resultingfrom anthropogenic inputs to the atmospheremay have serious ecological, economic, andsocial consequences. These changes andconsequences were carefully documented inrecent reports by the Intergovernmental Panelon Climate Change (IPCC 1996, 1998). Be-cause these changes will not be uniform overthe world and specific regional changes willhave greater degrees of uncertainty (Shrinerand Street 1998), vigorous debates have arisenconcerning all aspects of projected globalchange. Certain facts and projections, how-ever, leave little room for debate (Mahlman1997). Atmospheric CO2 concentration variedover the past 160,000 years, and global tem-peratures were closely correlated with changesin CO2 concentration (fig. 1) (Barnola et al.1995, Raynaud et al. 1993). During this longperiod, atmospheric CO2 concentrations rarelyexceeded 300 µll-1 and commonly rangedbetween 180 and 250 µll-1, although recentevidence indicates that short-term increasesmay have been present since the last ice age(Wagner et al. 1999). In the last 150 years,however, CO2 concentrations have increasedfrom about 280 µll-1 to the current 360 µll-1,largely from burning fossil fuels (coal, oil, gas)and burning biomass from forests and grass-lands (fig. 2) (Friedli et al. 1986, Keeling et al.1995). These anthropogenic sources produceabout 7 Pg carbon per year (1 Pg = 1015g) ofwhich roughly 2 Pg is absorbed by oceans, 2 Pgis stored by land vegetation, and about 3 Pgremains in the atmosphere (Amthor 1995,Schimel et al. 1996). This 3 Pg of carbon isequivalent to about 1.5 µll-1, which is thecurrent annual rate of CO2 increase in theatmosphere. Depending on anthropogenic CO2
emissions in the future, the CO2 concentrationin the atmosphere will probably double to over700 µll-1 within the next 100 to 150 years. Thisdoubling of the CO2 concentration will havesignificant effects on global and regional cli-mate and on plant growth and competition.Global mean temperature has increased about0.5oC within the last 100 years as CO2 concen-trations have increased from 290 to 360 µll-1
(fig. 3) (Schneider 1990). Doubling of thecurrent atmospheric CO2 concentration mayincrease global temperatures by 1o to 5oC andelevate regional temperatures even more
(Mahlman 1997, Schimel et al. 1996). Despitevigorous argument as to the extent of thegreenhouse effect, radiative forcing of globaltemperature from increasing concentrations ofatmospheric gases is a physical fact, and thereis no reason to expect that global temperaturewill not track CO2 concentrations in the future,just as it did in the past (fig. 1).
B. Carbon Dioxide Effects on Plants
Plants and soils of terrestrial ecosystems aremajor global carbon pools. Although estimatesdiffer considerably and all plant and organiccomponents may not be included in theseestimates (see Amthor 1995), terrestrial plantscontain 490 to 760 Pg carbon and soil organicmatter contains 1,500 to 2,100 Pg carbon,compared to 760 Pg carbon in the atmosphere.Annually, plants photosynthetically fix about15 percent of the atmospheric carbon pool,while respiration and decomposition returnsimilar amounts of CO2 to the atmosphere (notethe annual cycling of CO2 in the atmosphere infigure 2). Because of uncertainties in theestimation of soil organic carbon pools, and theeffect of increasing atmospheric CO2 concentra-tion on these pools, the amount of soil organiccarbon is a major concern in calculations ofglobal carbon budgets. Because most soilorganic carbon originates from living plants,differences in plant response to increasingatmospheric CO2 concentrations and theproportion of fixed carbon entering root andsoil pools are very important research topics.
Carbon dioxide at twice the current atmo-spheric concentration has the potential toincrease productivity in many agriculturalcrops and forest trees by 20 to 50 percent(Ceulemans and Mousseau 1994, Eamus andJarvis 1989, Wittwer 1990). Increased produc-tivity is expected because photosynthetic ratein most plants is limited by current atmo-spheric CO2 concentrations, and increasingCO2 concentrations also may increase water-use efficiency, nitrogen fixation, and mycor-rhizal symbiotic effectiveness. In addition,increased CO2 concentrations may ameliorateother environmental stresses (e.g., low nutrientavailability, mild water stress, and O3 impacts).Photosynthetic rates of C3 plants may increaseby 10 to 100 percent with a doubling of atmo-spheric CO2 concentration (Kirschbaum 1994).However, leaf and whole-tree canopy responseswill differ, and the actual photosynthetic
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may provide information on the interactionsbetween increasing CO2 and other environmen-tal variables, while absolute response providesinformation on potential productivity increasesin highly productive systems that are majorfactors in global net primary production andcarbon storage. Information on carbon fluxand carbon storage in productive forest ecosys-tems, such as northern hardwoods and aspenstands, is critical for understanding forestresponses to global climate change.
To further complicate the picture, an increasein photosynthesis or net carbon fixation maynot be reflected in aboveground increases indry weight because changes in carbon alloca-tion may favor belowground components suchas roots, mycorrhizae, and other rhizosphereorganisms (Curtis et al. 1996, Hodge 1996,Jones et al. 1998, Körner and Arnone 1992,Loehle 1996). However, inputs to soil organiccarbon pools should be positively related toincreased productivity or increased carbonfixation. Quantitative estimates of changes insoil carbon storage are problematic becauselittle information is available about changes inthe various input components (e.g., litter, fineroot production and turnover, carbon allocationto soil organisms, and direct exudation into therhizosphere) (Metting et al. 1999). Althoughdifficult, these questions about productivityand the fate of fixed carbon can be answeredwith long-term field experiments with elevatedCO2 and natural ecosystems. Such informa-tion is critical for the development of carbonbudgets and potential responses of terrestrialecosystems.
Increased atmospheric CO2 concentrations notonly may increase growth, but also impactplant populations and community interactions.Many studies show that the physiologicalresponse of individual species treated in isola-tion does not reflect their response in competi-tive situations (Ackerly and Bazzaz 1995,Bazzaz et al. 1996, Groninger et al. 1995,Körner 1996, Mooney et al. 1991, Ward andStrain 1999). The majority of plants in bothtemperate and tropical ecosystems, and essen-tially all forest tree species, use the C3 pathwayof photosynthetic carbon fixation (Bowes 1993).Growth response to elevated CO2 of C3 plantsshould be greater than response of C4 plantsbecause photosynthetic rates of C3 plants arelimited by current CO2 concentrations, while C4
plants are near photosynthetic saturation(Bazzaz 1990, Bowes 1993, Kirschbaum 1994).
However, some C4 plants may respond toelevated CO2 with increased photosyntheticrates and increased growth (LeCain and Mor-gan 1998, Ziska et al. 1999). An increase ingrowth of C3 plants compared to C4 plantscould have significant consequences for speciescomposition in ecosystems containing bothkinds of plants. Superior growth of C3 plants isby no means certain because other environ-mental factors (e.g., water stress, higher tem-peratures) may favor the growth of C4 plants(Amthor 1995). Potential C3/C4 responses arewidely discussed in the literature, but ecosys-tems composed largely of such competitors areof minor importance in global net primaryproduction. Ecosystems dominated by C3
species, such as temperate and tropical forests,are far more important in both area and re-sponse to increasing CO2 than other biomes(Wilsey 1996), and competition among C3
species is more significant when changes inpopulations and loss of biodiversity are consid-ered. Competitive advantages among C3 spe-cies are difficult to predict because differentgrowth strategies, reproductive strategies, andallometric plasticity interact with CO2 andother environmental stresses (Ackerly andBazzaz 1995, Farnsworth and Bazzaz 1995,Groninger et al. 1995, Hunt et al. 1993,Mousseau et al. 1996). Indeterminate orsemideterminate flushing species capable ofrapid growth in rich environments may re-spond more rapidly to increasing CO2 thandeterminate species. In contrast, determinatespecies with more conservative growth strate-gies may be favored on nutrient poor ordroughty sites. Vegetative response, however,may not be a good predictor of competitiveability because reproductive responses mayalso be important for determining speciesfitness with changing climates (Farnsworth andBazzaz 1995).
C. Atmospheric Ozone
Atmospheric O3 is largely confined to twodistinct layers of the atmosphere, the tropo-sphere, and the stratosphere. The troposphereextends upward 10 to 15 km (6 to 10 miles)from the Earth’s surface. The stratosphereextends upward about 40 km above the tropo-sphere. These two parts (they are not distinctlayers because there is much mixing betweenthem) of the atmosphere are defined by theirtemperature gradients. Temperature in thetroposphere decreases with altitude from about
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18oC at the Earth’s surface to –56oC at theboundary with the stratosphere (the tropo-pause). In contrast, temperature in the strato-sphere increases with altitude from –56oC toabout 0oC at the top of the stratosphere (thestratopause) (Seinfeld and Pandis 1998). Thesetemperature gradients repeat in the mesos-phere and thermosphere, which are two morelayers that extend the atmosphere outward byan additional 100 km (60 miles). To put theentire atmosphere into perspective, it is but athin (90 to 160 km thick) shell around theEarth that measures about 1 percent of thediameter of the Earth (12,900 km). Tropo-spheric thickness is about 0.1 percent of thediameter of the Earth, and most humans (andother animals) live in the lowest 5 km (3 miles)of the troposphere. This thin envelope of gas,which we use as a dumping ground for allmanner of pollutants, is all that protects us,our crops and animals, and other naturalecosystems from rapid death from intenseultraviolet (UV) radiation from the sun, and it isall that maintains a livable surface tempera-ture.
The temperature gradients in the troposphereand stratosphere are very important globalclimate factors. The troposphere containsabout 80 percent of the mass in the atmo-sphere and is very chemically active. It con-tains water (liquid and gas), other gases (nitro-gen, oxygen, carbon dioxide, volatile organiccompounds, nitrogen oxides, ozone, and othertrace gases) and particulate matter (smoke,dust, soot, salt particles), all of which providemany potential chemical reactions and sites forchemical reactions. The troposphere is charac-terized by a temperature gradient that de-creases with height at about 6oC km-1, corre-sponding to a temperature decrease of about70o to 90oC between the Earth’s surface andthe tropopause. This temperature decreasewith height in the troposphere, coupled withepisodes of significant surface heating, leads torapid vertical movement of air parcels. Fur-thermore, vertical movement of air and hori-zontal temperature gradients in the tropo-sphere also lead to horizontal winds and turbu-lent mixing. Particularly important in energy,gas, and particulate movement is the turbulentEarth-surface atmosphere boundary layer thatfluctuates diurnally and extends upward froma few meters at night to several kilometersduring the day when high surface temperatures
increase turbulent vertical mixing (Dabberdt etal. 1993). In contrast, the stratospheric tem-perature gradient, which increases with height,inhibits vertical mixing, except in the tropo-pause. This temperature gradient in thestratosphere results largely from the produc-tion of O3 and absorption of UV radiation by O3.
Differences in tropospheric and stratosphericO3 concentrations are cause for much publicconfusion. Ozone in the troposphere (bad O3—harmful to plants and animals) ranges from 10to 80 nll-1 in pristine areas and may increase to150 to 200 nll-1 in certain urban areas (Miller etal. 1994, Taylor 1994). In contrast, O3 in thestratosphere (good O3—protects plants andanimals by absorbing harmful UV radiation)increases rapidly from about 40 nll-1 in theupper troposphere to over 10 µll-1 (10,000 nll-1)in the lower stratosphere, then decreases tonear zero concentration in the upper strato-sphere (Seinfeld and Pandis 1998). The strato-sphere contains about 90 percent of the atmo-spheric O3, and the peak concentrations in thelower stratosphere result from the interactionsof O3 precursors and UV radiation. Catalyticdestruction of O3 by halogens and nitrogenoxides in the stratosphere has created theseasonal ozone holes over the poles and de-creased mid-latitude O3 concentrations in thelast 30 years by about 15 percent (Prather etal. 1996, Seinfeld and Pandis 1998).
The production and destruction of O3 in theatmosphere is extremely complex and cannotbe covered in any detail here. (For discussionof O3 chemistry and various control strategies,see Derwent and Davies 1994, Krupa andManning 1988, Milford et al. 1994, Seinfeldand Pandis 1998, Wolff 1993). In the simplestof terms, O3 is produced in the presence ofsunlight at wavelengths less than 424 nm andvarious nitrogen, oxygen, organic, and inor-ganic compounds. Nitrogen oxides are themajor catalysts in the formation or destructionof O3. For example, nitrogen dioxide in thepresence of sunlight (hv) may produce thefollowing reactions:
NO2 + hv = NO + OO + O2 = O3 + M
and the back reaction that destroys O3
O3 + NO = NO2 + O2
M may be N2, O2, or any other molecule thatcatalyzes or stabilizes O3 formation. Many
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and forest trees (Ballach 1997, Karnosky et al.1996, Kozlowski and Constantinidou 1986,Taylor 1994, Wittwer 1990).
E. Carbon Dioxide and Ozone Interactions
Because elevated CO2 exposure usually in-creases photosynthetic rates, decreases sto-matal conductance, and increases resistance toother environmental stresses, it is generallybelieved that increasing atmospheric CO2
concentrations will offset the detrimentaleffects of increasing O3 concentrations (Allen1990). Results of recent studies on the inter-acting effects of CO2 and O3, however, arecontradictory. Studies with several differentspecies show that exposure to elevated concen-trations of CO2 may counteract decreases inphotosynthesis and growth caused by O3
(Dickson et al. 1998, McKee et al. 1995,Mortensen 1995, Volin and Reich 1996). Incontrast, other studies show that elevated CO2
did not protect against O3 (Balaguer et al.1995, Barnes et al. 1995). Most of thesestudies involved average responses of generalplant populations and did not examine geno-typic responses. However, there is a stronggenotypic response in Populus to both CO2
(Ceulemans et al. 1996) and O3 exposure(Karnosky et al. 1996, 1998; Kull et al. 1996).In the latter study, added CO2 did not amelio-rate the detrimental effects of O3 on photosyn-thetic parameters of two aspen clones differingin sensitivity to O3. In fact, the O3-tolerantclone appeared more sensitive to O3 (Kull et al.1996). Even in cases where added CO2 maycounteract the negative impact of O3 andincrease growth back to the control level, theadded O3 negated increased growth from CO2
(Dickson et al. 1998).
F. The Importance of FACE Systems
It has been recognized for some time thatexisting information and experimental tech-niques are not adequate for developing accu-rate predictions of ecosystem response to globalclimate change (Mooney et al. 1991). There is acritical need for large-scale experiments thatexamine all of the interactions and feedbacksinvolved in total ecosystem response to increas-ing CO2 (Körner 1996, Lee and Jarvis 1995,Mooney and Koch 1994) and other atmosphericgases such as O3 (Heck et al. 1998). It is evenmore important that these large-scale experi-
ments involve ecosystems, such as temperateforests, that are major factors in global carboncycles and sustainable economic systems.
The large amount of data about CO2 responsesgenerated with individual species in restrictedexperimental settings has provided muchuseful basic biological and physiological infor-mation. Short-term physiological measure-ments on individual species, however, cannotbe used to predict long-term species or ecosys-tem response. Long-term measurements ofindividual species response in competitiveenvironments are necessary for predictingecosystem response. While ecosystem re-sponses are very complex and highly variablein space and time (Bazzaz et al. 1996, Körner1996, Mooney 1996), techniques are availableto study species response within a communityor ecosystem context. Open-top chambers areuseful for studying communities of relativelysmall plant species, but chamber effects arealways present and complicate application tonatural systems (McLeod and Long 1999,Olszyk et al. 1986a, b). Open-air field systemsfor exposure of different agricultural crops withair pollutants such as sulfur dioxide (SO2)developed rapidly during the 1980’s (McLeod etal. 1985, 1991) and were soon applied to foresttree species (McLeod and Skeffington 1995).These concepts were rapidly adopted for CO2
exposure of both agricultural crops and naturalecosystems (Hendrey 1992, Hendrey andKimball 1994). These FACE systems (Free AirCarbon dioxide Enrichment) are large enoughthat the many complex interactions of water,gas, and energy fluxes; biological responses;and biogeochemical cycles can be studiedsimultaneously to determine realistic gasexchanges and resource balances. Suchstudies are necessary if we are to move fromunderstanding individual plant responses tounderstanding ecosystem responses to globalclimate change.
The rationale for FACE technology, develop-ment of exposure systems, performance analy-sis, relative costs, and early plant responseswere recently reviewed and discussed in somedetail (Allen 1992, Hendrey 1992, Hendrey andKimball 1994, Hendrey et al. 1999, Kimball1992, Koch and Mooney 1996, Lewin et al.1994, McLeod and Long 1999, Mooney 1996,Nagy et al. 1994, Pinter et al. 1996). The FACEtechnology initially developed in 1986 anddeployed in agricultural field trials in 1988 and1990 by George Hendrey’s group at
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Brookhaven National Laboratory has been usedin several agricultural systems around theworld. However, only three FACE experimentalsystems involve forest trees. The FACTS-I(Forest-Atmosphere Carbon Transfer andStorage) experiment is in a loblolly pine (Pinustaeda L.) plantation in the Duke Universityforest near Durham, North Carolina. Theprototype of this system was tested in 1993and began operation in 1994 (Ellsworth et al.1995). FACTS-II is a FACE system designed toexamine the interacting effects of elevated CO2
and O3, alone and in combination, on theproductivity, competitive interactions, andcarbon and nitrogen fluxes in a regeneratingnorthern hardwood ecosystem. This system,near Rhinelander, Wisconsin, was constructedin 1995 and 1996 and tested in 1997, and itbegan full operation in May 1998. The FACTS-II, Aspen FACE system is designed to test theresponse of aspen (Populus tremuloides Michx.),paper birch (Betula papyrifera Marsh.), andsugar maple (Acer saccharum Marsh.) duringdevelopment from seedling to mature tree.Additional FACE systems are being developedat Oak Ridge National Laboratory in a sweetgum (Liquidambar styraciflua L.) stand and in aplantation of hybrid poplars (Populus spp.) nearViterbo, Italy.
To be effective, FACE experiments must con-tinue for enough time to clearly separateresponse to treatment from response to sea-sonal environmental changes. Experimentsshould continue for two to three life cycles ofannual plants, 3 to 5 years for perennial grass-lands, and 10 to 15 years or longer for foreststands (Hendrey 1992). FACE systems providea technique for treatment of large areas (over700 m2 for each ring at Rhinelander) essentiallyfree of any chamber or changed microclimaticeffect, in which large numbers of plants (660trees per ring at Rhinelander) can interact withtheir associated micro- and macro-biologicalagents such as mycorrhizae and insect herbi-vores in a community response that closelysimulates a natural ecosystem. Initial con-struction costs and yearly operating costs for alarge FACE system are very high, but becauseof the large area and large number of plantsinvolved, costs per square meter or per plantare much less than with other exposure sys-tems such as open-top chambers (Kimball1992). For example, the area of one ring atRhinelander is about 100 times the area of astandard open-top chamber (700 m2 vs. 7 m2).Such large areas of treated plant material
produce huge economies of scale for bothscientific output and plant material productioncosts.
G. Unique Characteristics of the Aspen FACEProject at Rhinelander
The Aspen FACE project has four characteris-tics that set it well apart from all other forestFACE projects:
1. It is large. Twelve 30-m diameter ringsare spaced 100 m apart within a fenced32-ha site. Each ring contains 700 m2
of treatment area for a total experimen-tal area of 8,400 m2 (2,100 m2 pertreatment).
2. The Aspen FACE project is the only onein the world that combines CO2 and O3
exposures. The experiment is a fullfactorial design with three control rings,three CO2 rings, three O3 rings, andthree CO2 + O3 rings.
3. The trees will be exposed to the CO2 andO3 treatments throughout the experi-ment from small, 1-year-old plants tomature trees. Exposures throughoutthe lifetime of the plants and associatedorganisms contrast with both the Dukeand Oak Ridge FACE programs, whichbegan CO2 enrichments on large treesthat had developed under ambient CO2
concentrations.4. The experiment contains three tree
species common to the Lake Statesforests (trembling aspen, paper birch,sugar maple), including five clones ofaspen that differ in response to CO2 andO3. Thus, the experiment contains awide range of species and genotypesthat can be assessed for their responseto treatment and competitive interac-tions.
H. Multidisciplinary Approach
Research designed to answer questions aboutecosystem physiology provides the opportunityfor and, in fact, requires collaboration of scien-tists from many disciplines who normally donot work closely together. The simultaneousstudy of individual plant and leaf responses(photosynthesis, stomatal conductance, andcarbon allocation) in addition to whole systemresponses (soil CO2, stand water loss, energyexchange, and nitrogen dynamics) requires
12
expertise in many areas. The large number offactors in ecosystem physiology that must beconsidered (see, for example, table 3.1 inKörner 1996 and fig. 2.1 in Mooney 1996) ifCO2 responses, water and energy fluxes, andsoil processes are adequately addressed,requires such teamwork. Currently, at theAspen FACE site, 30 scientists are involved invarious aspects of CO2, O3, plant, insect, soil,and meteorological interactions, and there isroom for many more. In addition, the siteprovides an opportunity for training andhands-on research experience for researchassociates, undergraduate students, andgraduate students in a wide variety of researchareas. The economy of scale, and the closecooperation and sharing of mutually usefuldata will increase scientific output per unit ofresearch time and funds spent.
I. Aspen: Genetic Variation andEconomic Importance
Quaking or trembling aspen is the most widelydistributed native tree species in NorthAmerica. It ranges east to west from New-foundland and Labrador to Alaska and south tothe mountains of Mexico. A similar species,the Eurasian aspen (Populus tremula L.),ranges from Britain across Europe and Asia tothe Pacific Ocean (Barnes and Han 1993).Thus, two very similar species of aspen circlethe entire globe. Not only is trembling aspenthe widest ranging tree species, it may alsocontain the oldest and largest individual plantknown (Mitton and Grant 1996). A single clonein Utah is estimated to weigh more than 6million kg and be more than 1 million yearsold. Trembling aspen (and perhaps also P.tremula) may be the most genetically variableplant ever studied (Barnes and Han 1993,Mitton and Grant 1996). Such genetic diversityallows aspen to survive from sea level to treeline in a variety of plant communities, fromquite dry to very wet sites, and from shrubs0.5 m tall to trees 30 m tall. Response toatmospheric pollutants also differs amonggenotypes. Ozone-sensitive and ozone-tolerantclones have been found, and these clones arevery useful for studying growth and mechanis-tic responses to O3 exposure (Karnosky et al.1996) and as bioindicators of regional pollut-ants (Ballach 1997, Karnosky et al. 1999).Aspen is also an excellent indicator of ecologi-cal integrity and forms communities of high
biodiversity. Many birds and animals dependon aspen ecosystems for survival (Alban et al.1991, Kay 1997). Aspen stands in the Westprovide many benefits, such as forage forlivestock and wildlife, watershed protection,recreational sites, aesthetics, landscape diver-sity, and wood fiber (Bartos and Campbell1998). Aspen-birch stands are major compo-nents of the Lake States forests, making upabout 5.3 million ha or 16 percent of thecommercial forest lands. The Northeast con-tains an additional 1.3 million ha. Aspen-birchand maple make up about one-third of thegrowing stock in the Lake States region andprovide about 70 percent of the roundwoodharvest (Hackett and Piva 1994, Piva 1996). Inaddition, these productive forests play animportant role in carbon sequestration (Albanand Perala 1992). Aspen-birch-maple standsare also important aesthetic components ofnorthern forests, and their vibrant yellow, gold,and red leaves are major contributors to the fallcolor parade. Given the major importance ofthese northern forest ecosystems, any impacton productivity and biodiversity from atmo-spheric pollutants will have severe ramifica-tions throughout the Eastern U.S.
III. GOALS AND OBJECTIVES
Our long-term goal is to examine the interact-ing effects of elevated CO2 and O3, alone and incombination, on the resultant productivity,sustainability, competitive interactions, andcarbon and nitrogen fluxes in a regenerating,northern hardwood ecosystem under fieldconditions over its life history.
The specific objectives of the Aspen FACEproject are to:1. Develop a reliable CO2 plus O3 delivery
system2. Examine the interacting effects of elevated
CO2 and O3, alone and in combination, onaspen, sugar maple, and paper birch:a. growth, survival, productivity, and
sustainabilityb. carbon and nitrogen allocation and
sequestrationc. competitive interactions among species
and genotypesd. stress tolerance as regulated by foliar
defense compoundse. response to insects, diseases, and other
stresses
13
3. Examine ecosystem processes such aslitter decomposition, mineral weathering,and carbon and nutrient cycling
4. Parameterize and validate an ecophysiologi-cal process model of growth and develop-ment to scale individual tree responses tothe ecosystem level.
IV. EXPERIMENTAL METHODS
A. Site Description
Location
The Aspen FACE site (32 ha) is located innorthern Wisconsin near Rhinelander, Wiscon-sin (long. 45.6º, lat. 89.5º), on the HarshawExperimental Farm of the USDA Forest Service.The legal description of the site is SW80, sect.21, T37N, R7E, Cassian Township, OneidaCounty, Wisconsin, USA. The site is old agri-cultural land that was farmed for potatoes andsmall grains for more than 50 years. TheForest Service purchased the Farm in 1972 foruse as a short-rotation intensive culture andmixed-genetics forest research facility. About
80 percent of the 32-ha Aspen FACE site wasplanted with different hybrid poplar clones andsome larch from 1976 to 1990. The remainingarea reverted to old-field vegetation. All poplarand larch plantings were cleared from the sitein 1996 and 1997, all stumps in the ring areaswere pulled, and the rings were disked andplanted in rye covercrop in the summer of1996. Aspen clones, paper birch seedlings,and sugar maple seedlings were planted in thering areas in early June 1997.
Soil Properties
The Aspen FACE site is level to gently rollingPandus sandy loam (mixed, frigid, coarse loamyAlfic Haplorthod). The sandy loam topsoil(about 15 cm thick) grades into a plowlayer-clay loam accumulation layer (about 30 cmthick) and then grades back into a sandy loam,stratified sand, and gravel substratum. Occa-sional clay layers at 30 to 60 cm are foundthroughout the field, primarily in the northern16 ha. As a basis for future comparisons, soilswithin each ring were analyzed in 1997 (table1). Soil properties differed little among the 12rings. Of all soil properties measured, only
Table 1.—Summary of soil properties for the Aspen FACE site for 19971. (See detailed table of soilproperties in the appendix.)
Treatment Control CO 2 O3 CO2 +O3
Soil texture% sand 55.1 (3.58) 53.9 (2.60) 58.3 (1.98) 55.0 (2.94)% silt 36.1 (3.15) 37.7 (2.30) 35.3 (3.74) 37.4 (2.68)% clay 8.8 (1.31) 8.4 (1.04) 6.4 (1.87) 7.7 (0.72)
Gravimetricmoisture content
(-0.3 bar)
0.163 (0.0215) 0.171 (0.0220) 0.159 (0.0077) 0.166 (0.0091) (-15 bar)
0.060 (0.0049) 0.066 (0.0147) 0.060 (0.0093) 0.053 (0.0045)
(WHC)0.102 (0.0183) 0.105 (0.0097) 0.099 (0.0016) 0.114 (0.0052)
Db (Mg/m3) 1.27 (0.119) 1.31 (0.089) 1.31 (0.084) 1.43 (0.075)
pH 5.50 (0.263) 5.45 (0.596) 5.57 (0.530) 5.68 (0.425)
NH4+-N (µg N/g) 1.03 (0.772) 0.94 (0.450) 0.85 (0.294) 0.56 (0.202)
NO3
--N (µg N/g) 15.06 (11.392) 15.24 (4.149) 11.83 (5.410) 11.98 (14.748)
Total C (%) 1.54 (0.267) 1.68 (0.327) 1.59 (0.321) 1.31 (0.200)
Total N (%) 0.12 (0.016) 0.14 (0.027) 0.12 (0.028) 0.10 (0.019)
C:N 12.88 (0.779) 12.40 (0.435) 13.58 (0.702) 12.84 (0.654)
1 Values are treatment means with standard deviations listed in parentheses.14
total C and N (%) were significantly differentamong treatments (Percent C and N averagedslightly higher in the CO2 rings than in the CO2
+ O3 rings). There were no significant differ-ences among replications or gradients acrossthe field.
B. Study Design
The FACTS-II; Aspen FACE study is locatedwithin a fenced 32-ha field (fig. 6A) on theHarshaw Experimental Farm near Rhinelander,Wisconsin. The study contains 12 individualtreatment rings (fig. 6B,C), which are 30 m indiameter and spaced 100 m apart to minimizebetween-ring drift of CO2 and O3. The experi-ment is a full-factorial design with three controlrings (no added CO2 or O3), three CO2 rings,three O3 rings, and three CO2 + O3 rings. Thetreatments are replicated three times in each ofthree blocks from north to south across the site(fig. 7). Each ring is divided into east and westhalves, and the west half is further subdivided
into north and south quadrants (fig. 8). Theeastern half contains five aspen clones num-bered 8L, 42E, 216, 259, and 271 (E216 andE271 were grown with elevated CO2 fromrooting to out planting). The aspen clones areplanted at 1-m spacing as randomized pairswithin the eastern half of the ring, and therings are individually randomized so that clonalposition within each ring is unique. Thenorthwest quadrant of each ring is planted(1 m x 1 m) with alternating sugar maple andaspen clone 216, and the southwest quadrantis planted (1 m x 1 m) with paper birch andaspen clone 216. Each row is marked with anumber from west to east (1 through 29) and aletter or letter combination from north to south(AD, AC through Z) so that each tree has aunique pair of coordinates. For example, 15-Cis clone 216, the northern member of thatclonal pair (fig. 8). Complete identificationwould require the ring number, e.g., 1,4 (CO2 +O3) (fig. 7), and the number-letter coordinates.In addition, each tree is tagged with a uniquenumber ranging from 1 to 7920.
15
Figure 7.—Aspen FACE project, location of the individual treatment rings and facilities within the 32-ha site.
Warehouse
Field
Lab
Utility
Shed
Quonset
Hut
1,1
1,3
2,2
3,4
3,13,3
2,3
2,4
1,2
1,4
2,1
3,2
Control
Trailer
Control
Control
+CO2 +O3
+CO2 +O3
+CO2 +O3
+O3
+O3
+O3
+CO2
+CO2
+CO2
Webster Road
Gra
ce
La
ne
0 50 100 mSCALE
100 200 300 ft
N
Vaporizers
Receivers
Ozonator
1This site is located at:
USDA Forest Service
Harshaw ExperimentalFarm near Rhinelander,
WI.
LEGEND
Plot LocationsExterior Fence
Roads Instrument Shed
Fence line ozone monitoring
Meteorological Tower Locations
18
FA
CE
Rin
g M
apH
arsh
aw E
xper
imen
tal
Farm
, R
hine
land
er,
Wis
cons
in
12
34
56
78
910
111
213
14
AD
AM
A
AC
MA
MA
M
AB
AM
AM
AM
A
AA
AM
AM
AM
AM
AM
AM
AM
AM
AM
A
BA
MA
MA
MA
MA
M
CA
MA
MA
MA
MA
MA
DA
MA
MA
MA
MA
MA
M
EM
AM
AM
AM
AM
AM
A
FM
AM
AM
AM
AM
AM
AM
GA
MA
MA
MA
MA
MA
MA
HA
MA
MA
MA
MA
MA
MA
M
IM
AM
AM
AM
AM
AM
AM
A
JA
MA
MA
MA
MA
MA
MA
M
LA
BA
BA
BA
BA
BA
BA
B
MB
AB
AB
AB
AB
AB
AB
A
NA
BA
BA
BA
BA
BA
BA
B
OB
AB
AB
AB
AB
AB
AB
A
PB
AB
AB
AB
AB
AB
AB
QA
BA
BA
BA
BA
BA
BA
RB
AB
AB
AB
AB
AB
AB
SB
AB
AB
AB
AB
AB
A
TB
AB
AB
AB
AB
AB
UB
AB
AB
AB
AB
A
VA
BA
BA
BA
BA
B
WA
BA
BA
BA
BA
XA
BA
BA
BA
B
YB
AB
AB
A
ZB
AB
12
34
56
78
910
111
213
14
1516
1718
1920
2122
2324
2526
2728
29
42E
42E
E27
127
1A
D
42E
42E
E27
142
E27
1E
216
E21
6A
C
E21
627
18L
42E
42E
259
42E
8LE
271
AB
E21
627
18L
42E
42E
259
42E
8LE
271
259
AA
E21
68L
216
42E
271
E27
121
627
121
625
9E
271
A
E21
68L
216
8L27
1E
271
216
271
216
259
E27
18L
B
216
271
271
8L25
9E
271
271
E27
142
E25
9E
216
8LC
216
271
271
216
259
E27
127
1E
271
42E
E27
1E
216
259
E21
6D
8L27
121
621
642
E42
E42
EE
216
8LE
271
216
259
E21
68L
E
8L27
121
6E
271
42E
42E
42E
E21
68L
216
216
259
E21
627
1F
259
42E
216
E27
121
6E
216
8L25
9E
271
216
E21
625
9E
216
271
G
259
42E
216
271
216
E21
68L
259
E27
121
6E
216
271
271
E27
18L
H
E27
142
EE
216
271
271
8L8L
E21
6E
216
216
8L27
127
1E
271
271
I
E27
142
EE
216
8L27
18L
8LE
216
E21
68L
8L25
925
921
627
1J
E27
125
9E
271
8L25
925
927
127
125
98L
8L25
925
921
625
9K
E27
125
9E
271
42E
259
259
271
271
259
271
8LE
271
259
E27
125
9L
8L42
E21
642
E21
6E
216
E27
127
1E
216
271
216
E27
125
9E
271
M
8L42
E21
6E
216
216
E21
6E
271
271
E21
642
E21
627
1E
271
259
N
E27
125
921
6E
216
E21
625
927
1E
216
E21
642
E8L
271
E27
125
9O
E27
125
921
642
EE
216
259
271
E21
6E
216
216
8L42
E42
E25
9P
8L27
127
142
EE
271
8LE
271
E27
121
621
625
942
E42
E25
9Q
8L27
1E
216
259
E27
18L
E27
1E
271
216
216
259
259
8LR
271
259
216
216
8L21
642
EE
216
259
216
E27
125
98L
S
271
259
216
42E
8L21
642
EE
216
259
42E
E27
1E
216
T
E21
68L
42E
42E
E21
6E
271
8L42
E27
142
EE
216
U
E21
68L
42E
216
E21
6E
271
8L42
E27
1E
271
V
42E
E21
621
621
627
121
627
18L
E27
1W
42E
E21
621
68L
271
216
271
8LX
E21
621
6E
271
8L42
E42
EY
E21
621
6E
271
Z
1516
1718
1920
2122
2324
2526
2728
29
WE
SN
Fig
ure
8.—
A t
rea
tmen
t ri
ng
tree
ma
p s
how
ing
the
loca
tion
of
the
dif
fere
nt
asp
en c
lon
es in
th
e ea
ster
n h
alf
of
the
rin
g a
nd
th
e a
spen
-bir
ch a
nd
asp
en-m
aple
tre
es in
th
e w
este
rn h
alf
of
the
rin
g. Let
ters
an
d n
um
ber
s a
re t
he
x,y c
oord
ina
tes
an
d t
he
hea
vy lin
e in
dic
ate
s th
e “s
wee
tsp
ot”
or a
rea
of
mos
t u
nif
orm
ga
s co
nce
ntr
ati
on. T
rees
ou
tsid
e th
e lin
e a
re c
onsi
der
ed b
ord
er t
rees
.
19
open greenhouse bench with an overhead waterspray for 15 minutes twice a day. After at leasta week on the hardening bench, the rootedcuttings were transplanted to 0.5-l containers(Stuewe and Sons, Corvallis, OR 97333). Thepotting mix was peat-sand-vermiculite (2:1:1,v:v:v) and timed-release fertilizer, Osmocote 17-6-12 (1 g/l). Water was applied overhead for 15minutes twice a day.
Some of the aspen material (labeled E216 andE271) was raised with elevated CO2 to test theimpact of early exposure on subsequent re-sponse. Rooted cuttings of clones 216 and 271were transplanted into 0.5-l containers andgrown with ambient plus 350 µll-1 CO2 in agrowth chamber until outplanted. This mate-rial was treated as separate planting stockduring outplanting.
Maple and birch plants were grown from seedin the same type of containers and soil mix asthe rooted aspen cuttings. Birch seed wascollected under mature trees in HoughtonCounty, Michigan, during the late summer of1996. Birch seed was stored dry and sown ontop of containerized soil on March 7, 1997.After germination the plants were thinned toone plant per 0.5-l container for subsequentgrowth in the greenhouse.
Maple seed was collected in Baraga County,Michigan, during autumn and refrigeratedmoist with Captan fungicide in plastic bags.On March 15, 1997, two to three maple seedscontaining live embryos were planted 0.5 cmbelow the soil surface in each 0.5-l container.Germination of the stratified maple seed waspoor, so naturally germinated seed from thesame source location was also used. Naturallygerminated seed was collected and planted inthe containers on April 15, 1997.
Plant material had reached outplanting size bylate May 1997. The containerized stock ofaspen, birch, and maple was then graded,moved outdoors, and kept under 50 percentshade until planting. Plant material wasoutplanted into the FACE rings during June1997. A 10-cm-diameter hand-held gasoline-powered auger was used to drill planting holes.Each plant-root plus soil plug was removedfrom the container and firmly packed into theplanting hole by hand. Immediately afterplanting, the rings were irrigated. During the
establishment season, summer 1997, rainfallwas supplemented with irrigation when the soilappeared dry.
D. Site Safety
Safety is a major concern because of the largesize of the Aspen FACE site; the large numberof investigators, students, and techniciansinvolved; potentially dangerous farm equip-ment; high pressure cryogenic gases (CO2 andO2); and toxic ozone production. Generalaccess to the site is controlled with a 3.6-mdeer fence around the entire 32 ha and a card-operated electric gate on the access road.Michigan Technological University or ForestService personnel are present at the site 24hours each day during the summer operatingseason. We have developed a safety programthat involves written, video, and tailgate in-struction that covers areas such as powertools, electrical systems, farm equipment,storm warnings, lightning and wind protection,and Occupational Safety and Health Adminis-tration (OSHA) safety data for O3 and cryogenicgas exposures. Ozone exposure is of specialconcern because of human toxicity at high O3
concentrations. The O3 distribution linesaround the site are aboveground and containabout 4 percent (40,000 µll-1) O3 with theoxygen carrier gas. Direct exposure to such O3
concentrations via a broken line would beextremely dangerous, if not lethal. Ozoneexposure in the experimental FACE rings,however, is much lower because treatmentconcentrations range from 60 to 100 nll-1 in thecenter of the rings. Ozone concentrations nearthe vents may be much higher (150 to250 nll-1). Excess O3 in the lines is converted toO2 in a destruct unit and then vented into theair above the control shed. Potential exposurewithin the rings must be compared to OSHAstandards for a realistic assessment of danger.OSHA permissible standards for worker expo-sures are 100 nll-1 averaged for 8 hours and300 nll-1 for 15 minutes. Exposures over 300nll-1 are considered hazardous, particularly forsensitive people and others with chronic lungproblems. Based on these standards, O3
exposure of research personnel in the ringswould not be considered harmful. However, allprecautions are being taken to minimize O3
exposure of people working within the O3
exposure rings.
20
E. Micrometeorological Monitoring
Within-ring MicrometeorologicalMeasurements
The following meteorological parameters aremeasured at rings 1,2; 2,1; 3,3; and 3,4 (seefigure 7 for ring locations): air and soil tem-perature, relative humidity, photosyntheticallyactive radiation (PAR), net radiation, windspeed and direction, and soil water content (fig.9A). Air temperature and relative humidity aremeasured with Campbell CS500 probes(Campbell Scientific, Inc., Logan, UT 84321)consisting of platinum resistance thermistersand Vaisala capacitive 50-Y intercap humiditysensors (Vaisala, Inc., Woburn, MA 01801).Soil temperatures are measured with 24-gaugecopper/constantan thermocouples referencedto a Campbell T107 temperature probe (Fenwal
UUT51J1 thermister, Fenwal Electronics,Milford, MA 01757). Wind speed and directionare measured with Young 03001-5 wind sentrysets (R.M. Young Co., Traverse City, MI 49686);PAR with LI-COR LI-1905B quantum sensors(LI-COR, Inc., Lincoln, NE 68504); and netradiation with a Q7.1 net radiometer (Radiationand Energy Balance Co., Bellvue, WA 98006).Soil water content is measured with CampbellCS615 water content reflectometer probes, andprecipitation is measured at rings 1, 2, and 3,3with a TE525 tipping bucket rain gauge (TexasElectronics, Inc., Dallas, TX 75235). Data fromall the meteorological equipment are collectedwith Campbell Scientific CR10X data loggers.
The meteorological data are measured, re-corded, and reported at different intervalsdepending on the particular measurement(table 2). Wind speed, wind direction, PAR, and
**
*
***
**
*
*
Aspen/Maple
Aspen
Aspen/Birch
B. Belowground Instrument Array
*
= Minirhizitron tube
= Soil Lysimeter
= Soil Respiration Collar
= pCO2 Gas Well, Moisture Probe
=Soil pit: Soil temperature at 5,10,20,50, and 100 cm Soil moisture at 5,50, and 100 cm=RH, Temp, and PAR at 1-2 m
=Wind speed and direction at top of pole
=RH, Temp, PAR, Wind speed and direction at 0.25 m above canopy (adjustable)
=Boardwalks
*
A. Micromet Sensor LocationsN
Figure 9.—A treatment ring map showing the location of micrometeorological equipment and otherinstalled experimental sampling equipment. A. Meteorological monitoring equipment (see table 2).B. Belowground root growth and carbon flux monitoring equipment.
21
22
Tabl
e 2.
—A
spe
n F
AC
E m
ete
oro
logi
cal m
on
itorin
g (
ring
s 1
,2; 2
,1; 3
.3; 3
,4)
I.D. 1
011
I.D. 1
02I.D
. 124
I.
D. 8
I.
D. 8
Sca
nre
port
repo
rtre
port
Acc
epta
ble
Out
-of-
rang
eP
aram
eter
inte
rval
30 m
in2
hr24
hr
lim
itsop
erat
ion
2)
Win
d sp
eed
@ 2
& 1
0 m
5 se
cA
vgA
vg, m
ax (
w/ti
me)
0 to
55
Set
flag
(m s
-1)
Win
d di
rect
ion
@ 2
& 1
0 m
5 se
cA
vg/S
tdv
Avg
, sta
ndar
d de
viat
ion
-10 o
to
360o
Set
flag
max
(w
/tim
e)
PA
R @
2 m
5 se
cA
vgA
vg, m
ax (
w/ti
me)
-.01
to 2
.4S
et fl
ag3
reps
tota
lized
(mm
oles
m-2s-1
)
Net
rad
iatio
n @
2 m
5 se
cA
vgA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)-3
00 to
120
0S
et fl
ag(W
m-2)
Tem
pera
ture
3 r
eps
@ 2
m5
min
Avg
Avg
, max
(w
/tim
e), m
in (
w/ti
me)
-50
to 5
0S
et fl
agan
d 10
m (
o C)
Rel
ativ
e hu
mid
ity 3
rep
s @
2 m
5 m
inA
vgA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)0
to 1
20S
et fl
agan
d 10
m(%
)S
et to
100
if >
100
Soi
l tem
p pr
ofile
5 m
inA
vgA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)-5
0 to
50
Set
flag
(5, 1
0, 2
0, 5
0, 1
00 c
m)
3 re
ps (
o C)
Soi
l moi
stur
e pr
ofile
(w
ater
2 hr
Sam
ple
Avg
, max
(w
/tim
e), m
in (
w/ti
me)
0 to
1.1
Set
flag
cont
ent)
3 r
eps
@ 0
-30,
(%)
30-6
0, 1
00-1
30 c
m
Pre
cipi
tatio
nC
ontin
uous
Tota
lTo
tal
0 to
254
Set
flag
(rin
gs 1
,2 a
nd 3
,3 o
nly)
(mm
)
1
Arr
ay id
entif
ier.
The
arr
ay id
entif
ier
is th
e fir
st n
umbe
r in
the
data
arr
ay th
at is
cod
ed to
iden
tify
the
arra
y re
lativ
e to
dat
a su
mm
ary
inte
rval
and
the
para
met
ers
mea
sure
d.
2N
ote:
Out
-of-
rang
e fla
g in
itiat
es s
naps
hot o
f all
para
met
ers
for
first
10
out-
of-r
ange
eve
nts.
net radiation are measured every 5 seconds;soil temperature, air temperature, and relativehumidity are measured every 5 minutes.Average values for all parameters are reportedevery 30 minutes. Soil moisture is measuredand reported every 2 hours. Daily reportsinclude average, minimum, and maximumvalues for all parameters.
Background Meteorological Measurements
For comparison with the within-ring measure-ments, a 20-m meteorological tower is located
in an open field near the north boundary of theexperimental site (fig. 10) to provide near-surface, background measurements. Thetower site measurements include relativehumidity, wind speed and wind direction, PARand net radiation, air and near-ground surfacetemperature, soil temperatures, soil moisture,barometric pressure, evaporation, leaf wetness,and rainfall (table 3). For information aboutthese meteorological parameters, consult ourFACE website (www.fs.fed.us/nc/face orclimate.usfs.msu.edu/face/meteorology.html).
Figure 10.—Aspen FACE meteorological tower containing instruments to measure site backgroundmeteorological parameters (see table 3).
23
24
Tabl
e 3.
—A
spe
n F
AC
E m
ete
oro
log
ica
l mo
nito
ring
(a
mb
ien
t to
we
r)
I.D. 2
011
I.D. 2
02
I.D. 2
24I.D
. 10
I.D. 1
0S
can
repo
rtre
port
re
port
acce
ptab
leou
t-of
-ran
geP
aram
eter
inte
rval
30 m
in2
hr
24 h
r li
mits
oper
atio
n2
Win
d sp
eed
5 se
cA
vgA
vg, m
ax (
w/ti
me)
0 to
55
Set
flag
@ 2
, 5, 1
0, 1
5, 2
0 m
(m s
-1)
Win
d di
rect
ion
5 se
cA
vg/S
tdv
Avg
, sta
ndar
d de
viat
ion
-10o
to 3
600
Set
flag
@ 2
, 5, 1
0, 1
5, 2
0 m
max
(w
/tim
e)
PA
R @
2 m
5 se
cA
vgA
vg, m
ax (
w/ti
me)
-.01
to 2
.4to
taliz
ed(m
mol
es m
-2s-1
)S
et fl
ag
Net
rad
iatio
n @
2 m
5 se
cA
vgA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)-3
00 to
120
0S
et fl
ag(W
m-2)
Air
tem
pera
ture
@ 2
, 5, 1
0, 1
5, 2
0 m
5 m
inA
vgA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)-5
0 to
50
Set
flag
soil
tem
pera
ture
s (
0 C)
@ s
urfa
ce, 0
.25,
0.5
, 0.7
5, 1
.0, 2
.0 m
Rel
ativ
e hu
mid
ity5
min
Avg
Avg
, max
(w
/tim
e), m
in (
w/ti
me)
0 to
120
Set
flag
@ 2
, 5, 1
0, 1
5, 2
0 m
(%)
Set
to 1
00 if
> 1
00
Soi
l tem
p pr
ofile
@5
min
Avg
Avg
, max
(w
/tim
e), m
in (
w/ti
me)
-50
to 5
0S
et fl
ag5,
10,
20,
50,
100
cm
(0 C
)
Leaf
wet
ness
@ 2
m5
min
Sam
ple
0 to
999
99S
et fl
ag(K
ohm
s)
Soi
l moi
stur
e pr
ofile
(w
ater
con
tent
)2
hrS
ampl
eA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)0
to 1
.1S
et fl
ag1
rep
@ 0
-30,
30-
60, 1
00-1
30 c
m(%
)
Pre
cipi
tatio
nC
ontin
uous
Tota
lTo
tal
0 to
254
Set
flag
(mm
)
Eva
pora
tion
gaug
e (p
an)
5 m
inS
ampl
eS
ampl
e0
to 2
54S
et fl
ag(m
m)
Bar
omet
ric p
ress
ure
30 m
inS
ampl
eA
vg, m
ax (
w/ti
me)
, min
(w
/tim
e)60
0 to
106
0S
et fl
ag(m
b)
1 A
rray
iden
tifie
r. T
he a
rray
iden
tifie
r is
the
first
num
ber
in th
e da
ta a
rray
that
is c
oded
to id
entif
y th
e ar
ray
rela
tive
to d
ata
sum
mar
y in
terv
al a
nd th
epa
ram
eter
s m
easu
red.
2 N
ote:
Out
-of-
rang
e fla
g in
itiat
es s
naps
hot o
f all
para
met
ers
for
first
10
out-
of-r
ange
eve
nts.
Belowground Instrument Array
In addition to the meteorological measuringinstruments, a large array of equipment wasalso installed within each ring to measurebelowground processes (fig. 9B). The mecha-nisms that regulate carbon transformation andthe time-steps and flux rates of belowgroundcarbon and nitrogen are largely unknown(Vitousek 1994) and are a major component ofthe Aspen FACE project. Thirty soil respirationcollars were randomly placed in each ring (10in each quadrant) while the minirhizotrontubes (16 per ring), soil tension lysimeters,pCO2 gas wells, and TDR soil moisture probes(9 each per ring) were systematically placedalong the boardwalks within the treatmentrings for easy access and to minimize foottraffic on the soil within the rings. The exactring coordinates of all belowground carbon fluxinstruments and meteorological instrumentsare included in the overall Aspen FACE digitalsite maps (see the Aspen FACE web site,www.fs.fed.us/nc/face, and George Host at theNatural Resource Research Institute (NRRI),www.nrri.umn.edu/aspenface).
F. Experimental Variables Measured
Because of the large size of the Aspen FACEproject, the high construction and operatingcosts, and the large number of investigationsinvolved (see Section II: G and H), it is veryimportant to measure as many experimentalvariables as possible. The many experimentsinvolved have been separated into abovegroundand belowground studies primarily for simplifi-cation (table 4). However, several study areashave both aboveground and belowgroundcomponents. Measuring plant growth, compe-tition, and carbon and nitrogen fluxes from leafto ecosystem level requires cooperation amonginvestigators to maximize information gain andminimize duplication of effort.
Five general aboveground study areas and fourbelowground study areas each contain severalindividual areas for research. To facilitateresearch coordination and database manage-ment, closely related study areas are combinedinto subgroups, such as gas exchange andcanopy architecture. Scientists from thesesubgroups meet independently to organize andcoordinate future research so they can obtainmaximum information with a minimum expen-diture of research time and funding (see figures16 and 17 for examples of these subgroups).
25
Table 4.—Experimental variables measured in the Aspen FACE project
Aboveground studies Belowground studies
1. Photosynthesis/gas exchange 1. Root growth and turnoverLight response curves within the crown Soil coresA/Ci curves MinirhizotronsRespirationTranspiration 2. Soil carbon fluxesStomatal conductance Soil organic matterCanopy light environment Soil respirationLeaf chemistry Soil CO
2 concentrations
Soluble organic and inorganic carbon2. Canopy architecture and leaf phenology
Branching characteristics 3. Soil biota-chemistrySpring bud and leaf development Microbial processesFall bud-set and leaf senescence Nitrogen fluxes
Plant nutrients3. Leaf surface characteristics and cellular Root chemical content
antioxidantsStomatal density 4. Leaf litterLeaf wax chemistry Decomposition ratesLeaf wettability Chemical contentAntioxidant enzyme systemsAntioxidant chemical concentrations
4. Water relationsSoil moisturePlant and soil moisture stressTranspiration and water movement in plantsHydraulic conductivity
5. Insects and diseaseGypsy mothWhite-marked tussock mothAspen-blotch leaf minerForest tent caterpillarPoplar branch borerPoplar gall-makerAspen gall flyBirch leaf minerWhite-spotted poplar aphidSmoky-winged poplar aphidBirch leaf aphidLeaf-produced insect defense compounds
26
V. CARBON DIOXIDE/OZONE DELIVERYAND CONTROL SYSTEM
The overall system design for this type offacility, as implemented by Brookhaven Na-tional Laboratory, was described in Hendrey etal. (1993, 1999) and Lewin et al. (1994). TheAspen FACE facility described in this reportwas modified from these earlier designs. Thegeneric FACE system ring hardware consists ofa high-volume blower, a plenum pipe for airdistribution, and 32 vertical vent pipes foremitting CO2 and O3 into the exposure volume.The major subcomponents of the Aspen FACEfacility that will be described in more detailbelow (including modifications of the design toenable more uniform gas distribution andfumigation with ozone) are (1) the CO2 and O3
supply systems, (2) the fan and plenum sys-tem, (3) the vertical vent pipe system, and (4)the control system.
The set-point for the CO2 concentration withinthe Aspen FACE rings receiving elevated levelsof CO2 during the 1998 and 1999 growingseasons was 560 µll-1, 200 µll-1 above ambientCO2 concentrations and similar to the CO2
concentrations anticipated by 2060 (IS92femission scenario, Technical summary, IPCC1996). A constant set-point was chosen tosimplify analysis of system performance,although the system can operate in a modethat maintains a constant increment (e.g.,+200 µll-1) above ambient CO2 concentration. In1997, initial performance tests and tests ofcontinuous 24-hour operation were conducted.In 1998, the Aspen FACE CO2-enriched plotswere treated from dawn to twilight (when thesun elevation angle exceeded 6o from thehorizon) from May 1 to October 13 for 158 outof 166 days. In 1999, CO2 exposures were from0700 to 1900 from May 10 to September 30 for144 days.
The treatment target for the O3 concentrationwithin the Aspen FACE rings receiving elevatedO3 during the 1998 and 1999 growing seasonwas a daily episodic exposure that followed adiurnal profile based on actual O3 data col-lected at Leelenaw, Michigan, during thesummer of 1987 (Karnosky et al. 1996). Theseambient profiles were modified to more closelymatch regional 6-year averages (1978-1983)described in Pinkerton and Lefohn (1987).Before the start of the experiment, the average
shape of the diurnal curve (stepped sine wave)and the frequency classes of daily peak O3
concentrations were established. A protocolwas then devised whereby the site operatorpicked a peak value at the beginning of eachday, based on that day’s meteorological condi-tions and forecast. For example, for hot andsunny days, when O3 concentrations arenormally higher, a diurnal curve with a highmaximum O3 concentration (90 to 100 nll-1)was chosen. For cool and cloudy days, adiurnal profile with low maximum O3 concen-trations (50 to 60 nll-1) was chosen. Plantswere not exposed to O3 during rain or when theleaves were wet with dew. In 1998, the AspenFACE O3 plots were treated from May 3 toOctober 13 for a total exposure (Sum 0) of 97.8µll-1-h. In 1999, the O3 plots were treated fromMay 10 to September 30 for a total exposure of89.0 µll-1-h.
A. Carbon Dioxide Supply System
Carbon dioxide was obtained as a byproduct ofagricultural fertilizer manufactured frommethane and atmospheric nitrogen. Food-grade, liquified CO2 was delivered to the FACEsite by truck in 20,000-kg lots and transferredto two insulated receiving tanks with a totalstorage capacity of 110,000 kg (fig. 11A). Tankpressure was maintained at 1,725 kPa to keepthe CO2 in a liquid state. A refrigeration unitand an electric heater maintained this pressureregardless of demand for CO2 by the FACEcontrol system. Liquid CO2 was supplied to abank of eight ambient-air heat exchangers,which vaporize the CO2 as needed (fig. 11B).The gaseous CO2 was routed from the vaporiz-ers to the ring locations through high pressurecopper piping (see figure A3 in the appendix).Near each ring, a pressure regulator decreasedline pressure to 140 kPa above ambient. TheCO2 gas was piped from the regulator to theFACE ring through 5-cm polyethylene tubing.The CO2 supply lines were equipped with amanually actuated shut-off valve where theydiverged from the main system supply line, anda pneumatically actuated shut-off valve at eachFACE ring. Carbon dioxide flow was measuredby an electronic flow sensor and throttled by aKurz rotary ramp metering valve (Model 735,Kurz Instruments, Monterey, CA 93940) thatprovided an even, linear gradation of gas flowover the range 0 to 1,550 kg hr-1. The metering
27
valve was operated directly by the FACE controlprogram (described below). The CO2 gas wasinjected into the plenum immediately down-stream of the air supply fan.
B. Ozone Supply System
Medical-grade, liquified O2 was delivered to theFACE site by truck in 15,000-l lots and trans-ferred to an insulated receiving tank with atotal storage capacity of 23,000 l (fig. 11C).The O2 storage tank was equipped with vapor-izer coils that maintained tank pressure as O2
was withdrawn and a relief valve that protectedthe tank from overpressurization during low O2
demand. The oxygen gas used to make ozonewas routed through a regulator that decreasedthe pressure to 120 kPa above ambient. Thislow-pressure oxygen gas was then routed intothe ozonator building (fig. 11D) and then intoan ozone generator (Model Unizone MZ18X,Praxair-Trailigaz Ozone Co., Cincinnati, OH45249) capable of producing 16 kg per day ofO3 at a maximum O3 concentration of 6 percentby weight. The rate of O3 production could bemanually adjusted by varying the flow of O2
through the generator and by altering thepower to the generator electrodes. For thisexperiment, the flow of O2 was held constant atthe expected maximum usage rate of 2 l min-1
per O3 treatment ring, and the generator powerwas varied as needed to obtain enough O3 tosupply all the rings. The power setting wasadjusted when the site operator found that theO3 mass-flow controller was operating near itsmaximum or minimum settings. In practice,we found that this setting did not have to bechanged very often. The sum of the indepen-dently varying demands of the six treatmentrings tended to remain fairly constant overtime.
The O3 in O2 gas mixture was routed to thetreatment rings through stainless steel tubing(fig. 11E) (also see figure A4 in the appendix).At each treatment shed, the supply linebranched into two paths. One led to the mass-flow controller that governed the flow of O3 intothe treatment ring; the other led to a backpressure relief regulator, which was set to passa maximum of just over 2 l min-1 if the pressurein the supply line rose above 35 kPa. Thisexcess portion of the O3-laden oxygen streamwas piped through a stainless steel canisterfilled with magnesium dioxide catalyst, whichconverted the O3 back to O2. This canister was
sized to destroy a stream of 6 percent O3
passing at a rate of 4 l min-1, twice the maxi-mum flow rate that the back pressure regulatorcould pass.
This arrangement of centralized O3 production,O3 distribution control, and O3 destructionallowed a relatively constant production of O3
at the source while accommodating a broadrange of O3 demands at the individual rings. Ateach ring the metering of the O3 was rapidlyand accurately controlled using a mass-flowcontroller. Locating the O3 bypass regulatorsand O3 conversion units at the end of thesupply line for each O3 treatment ring keptresidence time of the O3 in the supply linesboth short and constant, regardless of the O3
demand at the ring. This stabilized the lossesof O3 as it traveled through the supply piping.We found that the average loss of O3 as ittraversed the piping system from the generatorto the furthest treatment ring (over 660 m) wasless than 10 percent.
C. Fan and Plenum
An octagon plenum was assembled 2 m outsideof the 30-m-diameter circle of vertical ventpipes (VVP’s) to minimize the impact of theequipment on vegetation within the study area(fig. 12). The plenum was made of 38-cm-diameter polyvinyl chloride (PVC) pipe con-nected to the fan at a ‘T’ by a 2 m-length of thesame pipe (fig. 13A). A radial fan (Model 18-BISW-21, Vyron Corporation, Wisconsin Rap-ids, WI 54494) provided air flow (102 m3 min-1
at 2.0 kPa pressure) around the plenum.
D. Vertical Vent Pipes
Carbon dioxide- or O3-enriched air was injectedinto a FACE ring at the vertical vent pipes(VVP’s) (figs. 12 and 13). This is the mostcritical control step in the free-air approachand determines how well gas enrichment iscontrolled within the FACE ring. The followingelements of the system are each adjustable tosome degree.
Upwind Control
Thirty-two VVP’s constructed from 15-cm-diameter PVC pipe were evenly spaced in a 30-m-diameter circle around the FACE ring (fig.
29
B
A
C
Figure 13.—Individual treatment ring gas distribution equipment. A. Control shed, gas injection fan,and connecting plenum pipe. B. Butterfly control valves. C. Vertical vent pipe with gas emitterports and baffles.
32
are the biggest problem in maintaining controlof gas concentration in a FACE system be-cause (1) transport from the VVP’s into the plotis very irregular in all four cardinal directions;(2) low wind speed means slower transport ofthe enriched air from the VVP’s to the sampleintake in the center of the ring for the gasanalyzer, increasing feedback delay; and (3)parcels of air differentially enriched with CO2
may move irregularly through the plant canopyand back into the plot.
Support Poles
For CO2 exposure of tall trees, two VVP’s wereconnected to each of sixteen 10-m-tall woodenpoles evenly spaced around the perimeter ofthe 30-m-diameter ring (fig. 12A). These polesare free-standing and are identical to thosecommonly used to support electric or telephonelines. Additional sections can be added to theexisting VVP’s as the trees grow.
Vertical Vent Pipe Valves and Emitters
The VVP’s were connected to 15-cm-diameterbutterfly valves (Model 323-79U, KeystoneValves and Controls, Inc., Houston, TX 77040),which were directly connected to the plenumpipe by a short length of 15-cm-diameter PVCpipe (figs. 12B and 13B). The valves werepneumatically actuated, and each was sepa-rately controlled by the computer-operatedcontrol system. These valves opened or closedaccording to wind direction averaged over a 10-second period. Each valve was connected to amanifold of 32 pneumatic valves actuated bythe control program (described below) via 24-volt AC solenoids. The pneumatic system waspressurized at 620 kPa with air from an aircompressor (model 7Z030, W. W. Grainger,Inc., Green Bay, WI 54304) and storage tanklocated in the control building at each ring.
The CO2 - or O3-enriched air was emitted fromhorizontally slotted ports cut into the VVP’s (fig.13C). The ports were 2.5 cm high and 16 cmwide, covering an included angle of 120o, andthe center of the slot pointed directly away fromthe center of the ring. The air stream leavingthe slot was directed against a baffle platepositioned 10 cm away from the pipe. Thebaffle system was modified from the enhanced
local mixing (ELM) system described byWalklate et al. (1996). The baffle plate wasmade from a strip of aluminum sheet (15 cmwide by 50 cm long) bent in a right angle alongthe center line of its width. This was mountedhorizontally in an inverted “L” orientation withthe top leg of the “L” pointing back towards thevent pipe. This baffle redirected the air streamcoming from the emitter port so that it movedhorizontally and downwards along the periph-ery of the ring. At the start of the experiment,five emitter ports were cut into each vent pipe,spaced at 25-cm vertical intervals from about0.5 to 1.5 m above the ground. As the treesincreased in height, additional ports andbaffles were placed higher up on the pipe, andsome of the lower ports were closed to matchthe release rates at differing heights above theground with the vertical wind profile. In 1998,the aluminum baffles were replaced with PVCrain-gutter sections cut in half and positionedto direct the gas flow downward as describedabove.
This emitter design differs from that used inprior FACE systems designed by personnel atthe Brookhaven National Laboratory. Thepurpose of this design was to more rapidly mixthe CO2 and O3 from the jets with the ambientair passing by the vent pipes as it moved intothe ring. Due to the phytotoxicity of O3, theconcentration of gas had to be decreased asrapidly as possible. However, it appears thatthis emitter and baffle arrangement increasedthe variability of the gas concentrations withinthe rings. Further studies are needed toquantify and, if possible, correct this increasedvariability.
E. Gas Enrichment Control System
Regulation of CO2 and O3 concentrations withinthe treatment rings as well as registration andlogging of all pertinent data were achieved viathree fully integrated subsystems: (1) wind andgas (CO2 and O3) concentration detectors; (2) acentral data acquisition and control system;and (3) a gas enrichment control program.Because of the number of rings in this experi-ment, the site was run by three parallel controlsystems, each monitoring four rings. Separatesampling systems were used to monitor thespatial uniformity of the enriched gases withinthe rings.
33
Wind and Gas Concentration Detectors
Wind speed was measured at the center of eachring, near the top of the canopy, by a sensitivecup anemometer (Model 100075, Climatronics,Bohemia, NY 11716) and wind direction with awind vane (Climatronics model 100076)mounted on a support pole in the center ofeach ring. The minimum detectable windspeed was 0.3 m s-1, and the wind vane wasreliable at wind speeds above 0.4 m s-1.
Carbon dioxide concentration within thecanopy at the center of each ring was continu-ously monitored with a non-dispersive infraredgas analyzer, or IRGA (Model LI-6252, Li-Cor,Inc., Lincoln, NE 68504) placed within the ringinstrument shed (figs. 6C and 13A). Air wassampled from a control point at the center ofthe ring and the inlet port was set just abovethe main portion of the canopy. The sampledair was pumped at 15 l min-1 through approxi-mately 20 m of 4.3-mm-diameter polypropylenetubing to the analyzer. Just before entering theanalyzer, air flow was restricted to 0.8 l min-1
for CO2 analysis and the remainder was di-verted to waste. Tubing used for all CO2 moni-toring was made from opaque, black polypropy-lene (black Impolene tubing, Burns IndustrialSupply Inc., Whitewater, WI 53190) with lowCO2 absorptivity and permeability, and highresistance to ultraviolet radiation.
Ozone concentration within the canopy at thecenter of each ring was continuously monitoredwith a UV absorption gas analyzer (Models 49and 49C, Thermo Environmental Instruments,Inc., Franklin, MA 02038). Sample air waspulled at 31 min-1 through 4.3-mm-diameterTeflon tubing by a pump connected to theexhaust side of the analyzer detector cell. Theanalyzer automatically compensated for thevacuum applied to the detector and gave a newO3 reading every 10 seconds. As a check onthe possibility that the O3 released in the plotsmight leave the site in phytotoxic concentra-tions, separate measurements of ambient O3
were made at four points on the periphery ofthe research site close to rings where O3 wasbeing released (fig. 7). Air for O3 analysis waspumped through 1.2-cm-diameter Teflontubing from intakes on the fence line to aseparate O3 analyzer (Model 8810, MonitorLabs, Inc., San Diego, CA 92131) in the controlsheds.
The CO2 and O3 analyzers were read at 1-second intervals. However, due to smearing ofthe sample within the 20-m-long sample tubesand the averaging occurring in the detectorcells and analyzer electronics, the 1-secondvalues were reported as “grab-samples,” repre-senting an averaging time of less than 4 sec-onds for CO2 and 10 seconds for O3.
Data Acquisition and Control System
The data acquisition and control subsystemswere located in a small shed adjacent to theFACE ring (figs. 6C and 13A). These sub-systems processed commands received on afiber optic link from the central control com-puter (see following section). The commandseither requested measurements from sensors(input) or changed the state of a device (out-put). Inputs included CO2 or O3 at the controlpoint, wind speed and direction, CO2 or O3
mass-flow rate, air temperature, atmosphericpressure, and photosynthetically active radia-tion (PAR). Other inputs included the status ofpower supplies, fan operation, and VVP valveactuation air pressure. Command signals wereconverted from analog to digital and digital toanalog, by IOP-AD and IOP-D “I/OPLEXER”modules (DuTec, Inc., Jackson, MI 49264).
Gas flow to the individual VVP’s was controlledwith a bi-directional DC motor controller thatpositioned the Kurz CO2 flow-metering valve(Model 735, Kurz Instruments, Inc., Monterey,CA 93940). Digital output signals turned theCO2 feedline quarter-turn valve (Model S90-WCB, Flow-Tek, Inc., Columbia, SC 29201) onor off and actuated 32 pneumatic pilot valves(Mac Valves, Inc., Wixom, MI 48096), which, inturn, opened or closed the 15-cm butterflyvalves (Model 323-79U), Keystone Valves andControls, Inc., Houston, TX 77040) at the baseof each VVP (figs. 12B and 13B). The mass-flow of CO2 was measured with a Kurz Instru-ments model 452 flow sensor (Kurtz Instru-ments, Inc., Monterey. CA 93940). With O3,the gas flow was monitored and controlled witha stainless steel mass-flow controller (Model840, Sierra Instruments, Monterey, CA93940).
34
Gas Enrichment Control Program
Due to several factors, it was not possible tocontrol gas enrichment by simply making thegas release directly proportional to wind veloc-ity. Principal causes of variation in transportand mixing are air turbulence, low wind speed,and other factors, such as time delays in thesystem. For this reason, a custom controlprogram was written to accommodate complexinteractions between the sampling and controlhardware. To optimize the operation of thecontrol program, an extensive operator inter-face was provided that allows the systemoperator to view both the present and historicaloperation of the system in either textual orgraphic modes. This interface allows theoperator to adjust the integrating and weight-ing functions of the control algorithm from thecomputer keyboard, so that the system can befine tuned as needed while the control systemis operating. Provisions were also made forbacking up data on removable media, reportingalarms, and accessing the control programfrom a remote terminal.
The FACE operation programs were controlledby three Intel Pentium processor-based per-sonal computers located in the main controlbuilding at the edge of the research site (fig.11F). A duplex fiber optic serial cable networkusing eight-channel multiplexed fiber to RS-232 converters (Model TC2800, TC Communi-cation, Inc., Irvine, CA 92606) was the onlydata link between the FACE control computersand the field (see figure A5 in the appendix).The primary purpose for using fiber optics wasto electrically isolate the control building andcomputers from the FACE rings and to isolatethe rings from each other in event of lightningstrikes. The multiplexed converters allowedseveral data streams to coexist on the samefiber pair and added fault tolerance andtroubleshooting capability to the fiber network.Each computer controlled the amount of CO2
and/or O3 metered into the air stream enteringthe plenums of four treatment rings based onwind speed and gas concentration sampled atthe center of each ring. An empirically derived,proportional-integrative-differential (PID)control algorithm, described in Hendrey et al.(1999), adjusts the amount of CO2 introducedinto the plenum. Another algorithm, monitor-ing both wind direction and wind speed, con-trols which VVP’s emit CO2-enriched air (Lewin
et al. 1994). These two algorithms work to-gether to maintain the desired concentrationwithin the central area of the FACE ring whileminimizing CO2 and O3 usage.
CO2 concentration control within the rings wasquite satisfactory with the new vent pipeemitter design. Seasonal 1-minute average CO2
concentration was within 10 percent of the 560µll-1 target concentration 80 percent of the timeand within 20 percent of target concentration96 percent of the time (table 5). Control perfor-mance was not as good as that previouslyreported (within 10 percent of the 550 µll-1 90percent of the time and within 20 percent oftarget 98 percent of the time) by Nagy et al.(1994) and Hendry et al. (1999). Controlperformance of the Aspen FACE system tendedto decrease as the summer progressed and toincrease with wind speed as was found previ-ously (Nagy et al. 1994).
Ozone concentration control performance wasnot as good as that found with CO2 but aver-aged within 10 percent of the target concentra-tion 66 percent of the time and within 20percent of target 83 percent of the time (table6). This degradation of control was probablyrelated to the very low O3 target concentration(50 to 100 nll-1) and to the daily difference in O3
target concentration imposed by the episodictreatment regime. Ozone monitors, samplingair on the site perimeter fence (fig. 7) and at aWisconsin Department of Natural Resources airmonitoring station at Trout Lake, Wisconsin,provided hourly average ambient O3 concentra-tions for comparison with ring treatmentconcentrations. Plots of daily average 1-hourmaximum O3 concentrations clearly showedthat daily target O3 exposures within thetreatment rings were not detected at thefenceline, and that fenceline O3 concentrationswere the same as that at Trout Lake, indicatingthat the fenceline measurements were similarto regional ambient O3 concentrations (fig. 14).
Monthly average O3 concentrations and Sum 0values for the Aspen FACE project for 1998also showed that the fenceline exposures didnot differ from regional ambient exposures, andthat the seasonal exposures within the treat-ment rings (Sum 0 values, 97.8 µll-1-h vs. 65.3µll-1-h) were close to the 1.5x ambient O3 targetexposure originally planned (table 7). Moredetailed O3 exposures were compiled for the
35
1999 exposure season (table 8). Maximumdaily mean O3 exposures tended to decreaseduring the growing season, because the num-ber of hours each day with high O3 targetconcentrations decreased. Maximum 1-hourmeans were similar throughout the growingseason because there were always several daysduring the month with high (90 to 100 nll-1) O3
target concentrations. Seasonal Sum 0 expo-sures (0700-1900) for ambient and the treat-ment rings were 61.9 µll-1-h and 89.0 µll-1-hrespectively. The seasonal ring average Sum40 and Sum 80 exposures were 31.9 µll-1-h and3.6 µll-1-h, respectively (table 8). An example ofdaily diurnal O3 exposures (1-hour means) isgiven in the appendix (table A3).
Within-Ring Gas Distribution
A computer-controlled, multiple-port, select-able-sequencing sampler (MP3S) (Hendrey et al.1993, 1999) was set up in CO2 enrichment ring1,2 to collect CO2 data from 32 sample portsarranged in two layers (0.5 and 1.5 maboveground) within the controlled experimen-tal area. This array sampled a cylindricalvolume of 1,062 m3 (2 m height, 26 m diam-eter). Another sampler, made from stainlesssteel and Teflon with 23 sampling ports ar-ranged in a single layer 1.5 m aboveground,was installed in an O3 enrichment ring (1,4).The outer 2-m zone of the 30-m-diameter FACErings did not contain sample ports because thisarea was considered a mixing zone in whichexperimental CO2 and O3 concentrations werenot controlled. Samples were drawn sequen-tially from each port through the valve manifold
Table 5.—Carbon dioxide concentration control performance by month in 1998 for the Aspen FACEproject
CO2 and CO2 plus O 3 treatment rings
1,21 1,4 2,2 2,4 3,2 3,4 - - - - - - - - - - Percent - - - - - - - - - -
May 81.72 82.7 85.0 83.8 80.5 82.6
June —-3 83.9 87.1 84.5 82.0 84.5
July 88.5 81.4 82.9 79.3 74.0 79.3
August 79.6 79.8 80.7 78.0 67.5 77.9
September 80.1 79.7 83.3 78.9 71.3 80.0
October 79.8 77.8 77.2 77.4 64.9 74.7
Seasonalaveragewithin 10% 81.6 81.4 83.6 80.8 74.7 80.6
Seasonalaveragewithin 20% 96.1 96.0 96.5 95.3 94.2 95.8
1 1= North replicate, 2 = Center replicate, 3 = South replicate; 2 = CO2 exposure ring, 4 = CO
2 plus O
3
exposure ring. 2 Percentage of time the 1-minute average CO
2 concentration was within 10 percent of the 560 µl1-1 target
concentration. 3 Ring 1,2 was out of service in June because the control shed was destroyed by fire.
36
and sent to the CO2 or O3 analyzer. A 15-second purge time was used between sequen-tial samples, followed by a 45-second observa-tion period. Information collected from thesesamplers was used to document the spatialuniformity of the CO2 and O3 concentrationswithin the rings.
Gas concentrations within the rings increasedfrom the target concentration (560 µll-1 CO2) atthe ring center or CO2 control point out to theVVP’s (fig. 15). In this example of CO2 concen-tration contours, CO2 increased from 560 µll-1
at the center of the 26-m experimental area to
Table 6.—Ozone concentration control performance by month in 1998 for the Aspen FACE project
O3 and O3 plus CO 2 treatment rings
1,31 1,4 2,3 2,4 3,3 3,4 - - - - - - - - - - Percent - - - - - - - - - -
May 64.12 69.5 63.9 67.6 66.2 60.2
June 72.3 78.4 72.3 76.0 70.0 67.4
July 63.1 74.2 67.7 73.0 64.4 59.0
August 67.8 61.1 62.1 62.0 69.6 65.0
September 61.8 67.5 60.8 66.4 63.0 60.9
October 62.4 77.4 66.0 70.8 63.9 61.6
Seasonalaveragewithin 10% 62.2 71.4 65.5 69.3 66.2 62.4
Seasonalaveragewithin 20% 84.0 83.9 82.6 83.7 83.1 83.5
11 = North replicate, 2 = Center replicate, 3 = South replicate; 3 = O3 exposure ring, 4 = CO
2 plus O
3 expo-
sure ring. 2Percentage of time the 1-minute average O
3 concentration was within 10 percent of the target concentra-
tion.
640 µll-1 near the outer borders. This was anincrease over target concentration of about 14percent across the ring, although a smallportion of the experimental area (northeastquadrant) was more than 20 percent higherthan the target concentration. The CO2 con-tour plots are generally bowl shaped withhigher concentrations near the VVP’s. Daily,weekly, and monthly spatial uniformity variedbecause of variability in wind speed and direc-tion, temperature, and solar radiation—allfactors that affect atmospheric stability (Nagyet al. 1994).
37
0
20
40
60
80
100
120
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
Days of the month
Ozo
ne
co
nc
en
tra
tio
n (
nl
l-1
)
Trout Lake North Fence South Fence
East Fence West Fence Daily Target
Figure 14.—Comparison of fenceline and regional ambient O3 concentrations with daily O
3 treatment
concentrations for July 1998. Data lines show maximum 1-hr average O3 concentrations for each
day. Trout Lake and the west fence are Wisconsin Department of Natural Resources regional airquality test stations.
38
Table
7.—
Mon
thly
ave
rage
O3 c
once
ntr
ati
on a
nd
Su
m 0
va
lues
for
th
e A
spen
FA
CE
pro
ject
du
rin
g th
e 1
99
8 e
xpos
ure
sea
son
(a
mbie
nt
O3
con
cen
tra
tion
s a
re c
ompa
red
to
the
O3 e
xpos
ure
s w
ith
in t
he
trea
tmen
t ri
ngs
)
May
Ju
ne
July
A
ug
S
ep
O
ct 1
998
Sea
son
Mea
n S
um 0
Mea
n S
um 0
Mea
n S
um 0
Mea
n S
um 0
Mea
nS
um 0
Mea
nS
um 0
Mea
nS
um 0
nll-1
µll-1
-hnl
l-1 µ
ll-1-h
nll-1
µll-1
-hnl
l-1 µ
ll-1-h
nll-1
µll-1
-hnl
l-1 µ
ll-1-h
nll-1
µll-1
-h
Am
bien
t fen
celin
eN
orth
4516
.635
12.5
3211
.944
13.6
4111
.129
2.1
37.7
67.8
Sou
th42
15.6
3211
.731
11.5
4112
.635
9.3
251.
834
.062
.5E
ast
4416
.431
11.3
2710
.037
11.4
34 9
.224
1.8
32.8
60.1
Wes
t48
17.8
3613
.032
12.0
4313
.441
11.0
292.
138
.269
.3
Trou
t Lak
e47
17.4
3412
.332
12.0
4112
.738
10.2
282.
036
.766
.6m
ean
65.3
Rin
g 1,3
5217
.955
19.7
5721
.259
18.4
6417
.338
2.8
54.2
97.3
1,4
5217
.255
19.9
5520
.564
19.8
6417
.338
2.8
54.7
97.5
2,3
5418
.657
20.5
5821
.658
18.0
6517
.639
2.8
55.2
99.1
2,4
5318
.357
20.3
5721
.262
19.1
6517
.639
2.8
55.5
99.3
3,3
5318
.155
19.7
5620
.859
18.3
6517
.637
2.8
54.2
97.3
3,4
5017
.555
19.7
5721
.257
17.8
6317
.038
2.8
53.3
96.0
mea
n97
.8
Ozo
ne m
eans
and
sum
s ar
e fo
r th
e tr
eatm
ent –
tim
e in
terv
al:
May
, Jun
e, J
uly
: 07
00-1
900;
Aug
ust:
090
0-19
00; S
epte
mbe
r: 1
000-
1900
;O
ctob
er 1
-12:
100
0-19
00.
Sta
rt-t
ime
of th
e O
3 tr
eatm
ent w
as d
elay
ed la
te in
the
seas
on b
ecau
se o
f dew
on
the
leaf
sur
face
s.
39
Table
8.—
Ma
xim
um
da
ily a
nd
hou
rly m
ean
O3 c
once
ntr
ati
on f
or e
ach
mon
th o
f th
e 1
99
9 e
xpos
ure
sea
son
. S
um
40
an
d S
um
80
O3
expos
ure
s a
re a
lso
give
n f
or e
ach
mon
th.
Mon
th o
f O3
expo
sure
Rin
gM
ayJu
neJu
lyA
ugus
tS
epte
mbe
rTo
tal
Max
imum
dai
ly m
ean1
6981
6450
76(µ
l1--1
h)1,
3M
axim
um 1
-h m
ean
9199
9191
100
Sum
402
(µll-1
-h)
5.2
9.5
8.2
6.5
3.3
32.8
Sum
80
(nl
l-1-h
)29
61,
492
810
746
320
3.7
Max
imum
dai
ly m
ean
7281
5654
781,
4M
axim
um 1
-h m
ean
9199
116
9210
0S
um 4
05.
19.
75.
96.
83.
430
.9S
um 8
026
71,
513
382
641
293
3.1
Max
imum
dai
ly m
ean
7582
6453
782,
3M
axim
um 1
-h m
ean
9310
191
9210
0S
um 4
05.
39.
77.
86.
33.
432
.5S
um 8
030
41,
501
834
806
361
3.8
Max
imum
dai
ly m
ean
7380
6553
782,
4M
axim
um 1
-h m
ean
9099
9591
100
Sum
40
5.2
9.8
8.5
6.8
3.4
33.8
Sum
80
273
1,55
787
574
132
73.
8
Max
imum
dai
ly m
ean
6878
6053
763,
3M
axim
um 1
-h m
ean
9199
106
9510
0S
um 4
05.
19.
25.
25.
53.
128
.2S
um 8
033
31,
546
758
837
290
3.8
Max
imum
dai
ly m
ean
7281
6553
783,
4M
axim
um 1
-h m
ean
9010
190
9110
0S
um 4
05.
29.
78.
46.
83.
433
.4
Sum
80
296
1,51
678
066
731
73.
6S
um 4
0 rin
g m
ean
31.
9S
um 8
0 rin
g m
ean
3.
6
1
The
max
imum
dai
ly m
ean
O3
conc
entr
atio
n (n
ll-1)
is th
e av
erag
e of
24
one-
hour
mea
ns fo
r on
e da
y in
any
par
ticul
ar m
onth
. T
he d
ay-o
f-th
em
onth
with
max
imum
O3
conc
entr
atio
n m
ay d
iffer
bec
ause
the
epis
odic
O3
trea
tmen
t diff
ered
from
day
to d
ay.
2
Sum
40
(µll-1
-h)
and
Sum
80
(nll-1
-h)
are
the
tota
l hou
rly m
ean
O3
conc
entr
atio
n ov
er 4
0 an
d 80
nll-1
, res
pect
ivel
y. 1
999
seas
onal
Sum
0 e
xpo-
sure
s (0
700
to 1
900)
for
fenc
elin
e an
d re
gion
al a
mbi
ent,
and
for
the
trea
tmen
t rin
gs w
ere
61.9
µll-1
-h, a
nd 8
9.0
µll-1
-h.
40
-10
-5
0
5
10
15
-15-15 -10 -5 0 5 10 15
600
680
640
620
640
620
560
560560660
600
580
Distance from Plot Center (m)
Dis
tanc
e fr
om P
lot
Cen
ter
(m)
µll-1 CO2
N
Figure 15.—Isolines of CO2 concentrations within the multiport-equipped CO
2 treatment ring. Isoline
contours show the spatial variability of CO2 within the ring at 1.5 m above the ground. Contours
begin (circle in the figure) at 2 m inward from the vertical vent pipes. Data are average concentra-tions from sunrise to sunset for August 3 to September 26, 1998.
41
VI. FUNDING PARTNERS, RESEARCHCOOPERATION, AND RESEARCH APPROACH
FACE programs that attempt to study ecosys-tem processes require large exposure rings,some minimum amount of replication (threereplications for the FACTS-II, Aspen FACEproject) for statistical analysis, and a largenumber of cooperating scientists from differentdisciplines. Initial construction costs andyearly operating costs for such large systemsare too great to be covered by any one govern-ment agency out of research funds allocated toecosystem or global change studies. Researchpersonnel from Michigan Technological Univer-sity (MTU); Rhinelander Forestry Sciences Labof the U.S. Department of Agriculture, ForestService, North Central Research Station (USDAFS NCRS); Brookhaven National Laboratory(BNL); the University of Wisconsin; and the
University of Michigan developed the initialresearch proposal that was funded with aTerrestrial Ecology and Global Change (TECO)grant, a joint program with backing from theNational Science Foundation (NSF)/Depart-ment of Energy (DOE)/USDA/National Aero-nautics and Space Administration (NASA).These funds provided startup money for theAspen FACE project and generated severalother funding partners (fig. 16). Major continu-ing supporters of the Aspen FACE project, inaddition to the USDA FS NCRS, MTU, and BNL,are DOE, the USDA FS Northern GlobalChange Program and the Canadian ForestService (CFS).
The Aspen FACE project is the largest FACEsystem in the world. It is unique because itinvolves both CO2 and O3 exposures and threespecies of northern hardwood trees from
Figure 16.—Funding partners, research partners, and research approach of the Aspen FACE project.
42
Modeling andremote sensing
Site engineering
control systemsGas exchangeand canopy
architecture
Insects anddiseases
Biochemical and
molecular
responses
Belowgroundprocesses
Databasemanagement
Research Approach
Mississippi State
University
University ofMichigan
University ofIllinois
University ofKuopio-Finland
Canadian
Forest Service
Estonian Institute
of Ecology-Tartu
University of
Wisconsin-Madison
University of
Minnesota-Duluth
US Forest ServiceMichigan Tech University
Brookhaven National
Laboratory
SlovakianForest Service
Research Partners
University ofWisconsin
Foundation
CanadianForest Service
Michigan Tech
University
U.S. ForestService Global
ChangeU.S.
Departmentof Energy
US Departmentof Agriculture
NCASI
National ScienceFoundation
US Forest Service
Michigan Tech UniversityBrookhaven National
Laboratory
FinnishAcademy of
Science
Funding Partners
US Forest ServiceMichigan Tech University
Brookhaven National
Laboratory
Environmental
monitoring
quality control on the collected data. Cur-rently, data are manually transferred biweeklyfrom the data-logger storage modules at theFACE site to a desktop personal computer atthe NCRS, FSL, Rhinelander, where preliminaryquality checks are made. This manual down-loading of meteorological data will eventually bereplaced with automated electronic download-ing of data from the data-loggers to personalcomputers at the FACE study site via a fiberoptics line, followed by a manual transfer of thedata to a desktop personal computer at theRhinelander FSL at the end of each month.
At the Rhinelander FSL, ASCII data files spe-cific to each month, ring/tower, and set ofmeteorological variables are created and thentransferred via file transfer protocol (FTP) to theEast Lansing FSL. There, the ASCII data filesare reformatted and subjected to an additionalquality control process involving the flagging ofmissing data and removal of data outliers usingVisual Basic macros within Microsoft Excel.The final meteorological data files in MicrosoftExcel 7.0 format are then placed on a ForestService FTP server that is accessible to otherprincipal investigators via the world wide webfor the Aspen FACE (www.fs.fed.us/nc/face) orfor direct meteorological information(climate.usfs.msu.edu/face/meteorology.html).A data directory hierarchy has been establishedthat organizes the data files by year, month,and ring number or tower site. Users of themeteorological data files can download specificfiles from the web site by clicking the appropri-ate file icons. Information on the file names,file formats, and directory structure for the FTPsite is being developed in the form of aREADME file that can also be downloaded byusers as needed.
C. Operational Performance Data
The operational performance data at the AspenFACE site is managed by BNL personnel aspart of the overall FACE Database ManagementPlan under the direction of G. Hendrey. TheData Manager is BNL’s Internet gateway to allFACE databases and is available online at(www.face.bnl.gov).
The BNL web site provides real time perfor-mance Quickbooks: FACE data archive com-pact disks; data reduction pathways; qualityassurance issues and procedures; long termarchive at the Carbon Dioxide Information
Analysis Center (CDIAC) at Oak Ridge NationalLaboratory (ORNL) in Oak Ridge, Tennessee;and fair use policy. That policy states that thedata sets available in this site are provided as acourtesy as part of our ongoing commitment toprovide experimental systems, software tools,and data sources for the research community.
We have adopted the fair use policy suggestedby CDIAC and the Ameriflux scientific commu-nity, namely,
“Kindly inform the appropriate PrincipalInvestigators of how you are using sitedata and of any publication plans. If thePrincipal Investigators feel that theyshould be acknowledged or offeredparticipation as authors, they will let youknow and we assume that an agreementon such matters will be reached prior topublishing and/or use of the data forpublication. If your work directly com-petes with the Principal Investigator’sanalysis, they may ask that they havethe opportunity to submit a manuscriptbefore you submit the one that uses theirdata. In addition, when publishing,please acknowledge the agency thatsupported the research.”
D. Biological Data
Biological data from investigators in the scienceteam subgroups is maintained in an experi-mental format designed by each investigator.Data sharing, quality assurance, and statisticalanalysis also are the responsibility of eachPrincipal Investigator. Sharing of data and fairuse of other’s data are strongly encouraged tomaximize interpretation of interactions betweenenvironmental variables, and to maximizescientific information obtained from the AspenFACE project.
VIII. PROCESS MODELING AT THEASPEN FACE SITE
The modeling efforts at the Aspen FACE siteprovide for an integration of the meteorological,biological, and operational data collected in theexperiment. The fundamental purpose ofprocess modeling work is to allow us to ex-trapolate the results of the study beyond therange of conditions used in the experimentaldesign. The target O3 concentrations, forexample, are not extraordinarily high—they are
45
atmospheric variables, and visualize theiroutcomes in a straightforward way. The flex-ibility and highly interactive nature of controlsadopted by WIMOVAC makes it well suited as aplatform for both managing data and conduct-ing canopy-level simulations of FACE sites.
WIMOVAC effectively simulates multilayerhomogeneous vegetation canopies. Under themultispecies and structurally heterogeneousconditions imposed at the Aspen FACE site,however, the differences in initial plant archi-tecture and differential responses to treatmentsamong clones require a more detailed simula-tion of the plant canopy. For this reason, weare integrating elements of the ECOPHYSgrowth process model into the modeling plat-form. ECOPHYS is an individual-based pro-cess model that uses parallel computing strate-gies to calculate photosynthesis of individualleaves within a structurally heterogeneousforest canopy. It allows for different clonalarchitectures, differential response to tracegases, and competitive interactions amongtrees (Host et al. 1996, Isebrands et al. 2000).Both ECOPHYS and WIMOVAC are adaptingComponent Object Model (COM) protocols thatallow models written in different languages andresiding on different computers to communi-cate. These two modeling strategies are highlycomplementary and provide for both “bottom-up” (i.e., individual-based) and “top-down”(aggregation-based) modeling approaches.
In addition to simulation modeling, we areusing regression and other statistically basedapproaches to scale information from theindividual leaf to the canopy. These sample-based approaches provide a means of describ-ing whole-tree phenomena by instantaneousdata with information on specific leaf area,total leaf area, and numbers of leaves. Thismorphometric approach to scaling will allow usto compare biological responses among clones,treatment, and other factors within the experi-ment.
Lastly, there is an ecosystem scale of modelingthat incorporates aboveground and below-ground responses to treatments, such ascompetitive interactions among trees, alter-ations to carbon and nutrient cycles, and theresponse of soil and microbial pools. Thisecosystem approach will be important foraddressing long-term questions on nutrientcycling, carbon sequestration, and plant-insectinteractions under global change conditions.
IX. STATISTICAL CONSIDERATIONS ANDDATA ANALYSIS
The method of analysis chosen depends on thephysical design of an experiment, the selectionof treatments and levels of treatments, thesampling of experimental units for measure-ment, and the questions (hypotheses) wechoose to ask. Not all of the aforementionedfactors are defined during the design of anexperiment, especially an experiment as largeand complex as the Aspen FACE project. Forexample, when trees within treatment combi-nations are selected for measurement of physi-ological characteristics, are the same treesmeasured each time or is each measurementmade on a different random sample of individu-als within plots? This choice, which deter-mines whether data need to be treated asrepeated measures or as independent randomsamples, is commonly made after the experi-ment is designed and is often made differentlyby different investigators. Other examplesexist, all of them leading to the conclusion thatno single method of analysis will be rigorouslyapplicable to all data and the questions thatare asked of those data. Having said that,however, we put forth in this section someoverall considerations that will probably holdtrue over the life of the study. Within thatframework, we also include a sample analysisof early chlorophyll meter (SPAD) measure-ments.
The Aspen FACE experimental design, at thewhole-plot level, is three replications of arandomized complete block design with fourtreatment combinations. Subplots are estab-lished within whole plots and include mixturesof species (aspen, birch, maple) and mixtures ofgenotypes of the same species (clones of aspen).We assume it will be of interest to test forsignificant effects of whole-plot treatments(CO2, O3), whole-plot interactions (CO2 x O3),subplot treatments (clones—considering theaspen subplots), and interactions betweensubplots and whole-plot treatments (i.e., clonex CO2 x O3) on various dependent variables.This suggests that the application of analysis ofvariance, in some form, is appropriate (Steeland Torrie 1980). To apply analysis of vari-ance, we assume that replications are a ran-dom effect, treatments are fixed effects (expo-sure concentrations were clearly not chosen atrandom from all possible concentrations), andclones are fixed effects (again, not chosen atrandom from all possible genotypes within the
47
Table
9.—
Sa
mp
le d
ata
an
aly
sis
of c
hlo
rop
hyll
met
er (S
PAD
) ob
serv
ati
ons
ma
de
on s
ever
al tr
ees
of e
ach
clo
ne
wit
hin
th
e a
spen
subplo
ts
Deg
rees
Sou
rce
of v
aria
tion
Sum
of
ofM
ean
squa
res
free
dom
squa
res
f-ra
tios
Exp
ecte
d m
ean
squa
res
Who
le-p
lots
Rep
licat
ions
140.
422
70.2
10.
48ns
σ e(b)
2 +
43.
44 σ
e(a)
2 +
173
.77
σ r2
Trea
tmen
ts1,
871.
773
623.
924.
76 *
σ e(b)
2 +
39.
05 σ
e(a)
2 +
Q3
k t2
CO
225
6.96
125
6.96
1.96
ns
O3
1,51
1.41
11,
511.
4111
.53
*
CO
2 x
O3
92.6
11
92.6
10.
71ns
Err
or (
a)87
1.88
614
5.31
7.99
**σ e(
b)2
+ 4
3.99
σe(
a)2
Sub
plot
sC
lone
s94
4.72
423
6.18
12.9
8**
σ e(b)
2 +
Q2
k c2
Clo
nes
x Tr
eatm
ents
388.
7112
32.3
91.
78 *
σ e(b)
2 +
Q1
k ct2
Clo
ne x
CO
271
.62
417
.91
0.98
ns
Clo
ne x
O3
271.
824
67.9
63.
73**
Clo
ne x
CO
2 x
O3
51.2
84
12.8
20.
70ns
Err
or (
b)9,
189.
6850
518
.20
σ e(b)
2
Not
es:
Ove
rall
anal
ysis
by
gene
ral l
inea
r m
odel
s pr
oced
ure
(PR
OC
GLM
, SA
S®
Inst
itute
Inc.
, 198
8) w
ith r
eplic
atio
ns, t
reat
men
ts, r
eplic
atio
ns x
trea
tmen
ts (
Err
or (
a)),
clo
nes,
and
clo
nes
x tr
eatm
ents
spe
cifie
d in
the
“mod
e.”
Rep
licat
ions
, rep
licat
ions
x tr
eatm
ents
, Err
or (
a) a
nd E
rror
(b)
wer
e as
sum
ed r
ando
m; a
ll ot
her
effe
cts
wer
e as
sum
ed fi
xed.
Err
or (
b) is
a p
oole
d te
rm c
onta
inin
g va
riatio
n du
e to
rep
licat
ion
x su
bplo
t effe
ctin
tera
ctio
ns a
nd v
aria
tion
due
to s
ubsa
mpl
ing
(leaf
pos
ition
s an
d ag
es).
Var
iatio
n du
e to
CO
2, O
3, a
nd C
O2
x O
3 ef
fect
s w
as e
stim
ated
by
linea
rco
ntra
sts.
Int
erac
tions
bet
wee
n cl
one
and
trea
tmen
t com
bina
tions
wer
e al
so e
stim
ated
by
linea
r co
ntra
sts.
F-r
atio
s fo
r su
bplo
t effe
cts
and
Err
or (
a) a
ll us
ed E
rror
(b)
as
the
deno
min
ator
. F
-rat
ios
for
who
le-p
lot t
reat
men
ts a
re S
atte
rthw
aite
app
roxi
mat
ions
bec
ause
of u
nequ
al c
oeffi
-ci
ents
ass
ocia
ted
with
se(
a)2
in th
e re
plic
atio
n an
d tr
eatm
ent e
xpec
ted
mea
n sq
uare
s. F
-rat
ios
for
who
le-p
lot t
reat
men
t com
bina
tions
(si
ngle
degr
ee o
f fre
edom
ort
hogo
nal l
inea
r co
ntra
sts)
use
the
sam
e sy
nthe
size
d de
nom
inat
or a
s th
e F
-rat
io fo
r tr
eatm
ents
(sy
nthe
size
d de
nom
inat
or13
1.05
with
test
s on
1 a
nd 6
.19
degr
ees
of fr
eedo
m).
** =
pro
babi
lity
of f
due
to c
hanc
e <
0.0
1, * =
pro
babi
lity
of f
due
to c
hanc
e >
0.0
1 an
d <
0.05
, ns =
pro
babi
lity
of f
due
to c
hanc
e >
0.0
5.
48
species). In the data analysis sample (table 9),we consider SPAD readings taken from severaltrees of each clone within the aspen suplots ofeach whole plot. The model for the analysis is:
Xijk = m + Ri + Tj + RTij + Ck + CTjk + eijk
where Xijk is an observation, m is the experi-mental mean, Ri is the effect of the ith replica-tion, Tj is the effect of the jth treatment, RTij isthe interaction between the ith replication andthe jth treatment (whole-plot error or Error (a)),Ck is the effect of the kth clone, CTjk is theinteraction between the jth treatment and thekth clone, and eijk is a pooled subplot error(Error (b)).
Error (a) is a pooled component containingvariation attributable to replications x CO2,replications x O3, and replications x CO2 x O3.Error (b) is also a pooled estimate containingvariation attributable to replications x clonesand to variation among trees within clone-treatment-replication combinations. It wouldalso be valid to extend the model by one termto divide Error (b) into replication x clone andsubsampling terms.
We further test for effects of various treatmentsand their interactions, and for interactionsbetween clone and various treatment combina-tions by extracting appropriate sums ofsquares by orthogonal linear contrasts. Appro-priate f-tests are clearly identifiable by inspec-tion of expected mean squares and utilize theSatterthwaite approximation where neededbecause of imbalance in sampling (Steel andTorrie 1980).
For analyses that do not involve comparisonsamong effects within rings, block effects can betreated as fixed or random according to theparticular considerations of the individualinvestigator. For mixed model analyses utiliz-ing the split-plot design with random blockeffects and fixed treatment effects, block xtreatment variation should be evaluated todetermine the appropriate error structure ofthe model with regard to pooling or partitioningof the Error (a) term. The PROC Mixed compo-nent within the SAS® System software (SASInstitute, 1989-1996) is ideal for analysis ofmixed model designs and can readily incorpo-rate covariance, repeated measures, andspatial statistics components (Littell et al.1996). PROC Mixed is preferred for split-plotdesigns as it automatically calculates correct
error terms and degrees of freedom, and ad-justs for sampling imbalance. For models withentirely fixed effects, the PROC GLM compo-nent of the SAS® software is appropriate.
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XI. ACKNOWLEDGMENTS
We gratefully acknowledge the many dedicatedpeople who assisted in the construction of and/or daily operation of the Aspen FACE facility,including Brookhaven National Lab scientistsGeorge Hendrey, John Nagy, and Keith Lewinwho shared their BNL FACE technology andhelped us modify their design to meet ourneeds for dispensing both CO2 and O3; formersite manager Mark Kubiske and MarkColeman; current site engineers Jaak Soberand Scott Jacobson; the numerous graduatestudents and undergraduate students fromMichigan Tech, the University of Wisconsin,and the U.S. Forest Service. These peopleassisted in design, procurement, and construc-tion of the rings, control sheds, and gas distri-bution systems. We acknowledge the help ofMichael Bancroft, Engineer, Chequamegon-Nicolet National Forest, for site surveys andconstruction drawings, and Audra Kolbe andJohn Wright for help with the figures andgraphics in this document. Finally, we ac-knowledge the Wisconsin Department of Natu-ral Resources Air Quality Division for their helpin establishing and operating an Ozone Moni-toring network of Aspen FACE site boundariesduring the first 3 years of operation.
This research was partially supported by theUSDA Forest Service Northern Global ChangeProgram, the U.S. Department of Energy (DE-FG02-95ER62125), the National ScienceFoundation (DBI-9601942; IBN-9652675), theNational Council of the Paper Industry for Airand Stream Improvement (NCASI), the USDAForest Service, North Central Research Station,Michigan Technological University, and theCanadian Forest Service.
56
XII. APPENDICES
Table A1.—Relationships between soil matric potential and gravimetric water content for the AspenFACE site
Table A2.—Detailed soil properties for the Aspen FACE site for 1997Table A3.—Diurnal ozone concentrations for ring 1,4 of the Aspen FACE site for June 1999
Figure A1.—Aspen FACE site layout—RoadsFigure A2.—Aspen FACE site layout—Meteorological stationsFigure A3.—Aspen FACE site layout—Carbon dioxide supply linesFigure A4.—Aspen FACE site layout—Oxygen, ozone supply linesFigure A5.—Aspen FACE site layout—Fiber optic cableFigure A6.—Aspen FACE site layout—Underground electrical cableFigure A7.—Aspen FACE site layout—Irrigation lines
57
Table A1.—Relationships between soil matric potential and gravimetricwater content for the Aspen FACE site
Matric Gravimetric 1
potential moisture content Standard(-MPa) (%) deviation
0 38.2 3.18
0.006 34.7 2.46
0.010 30.3 2.39
0.030 Field capacity 16.5 1.48
0.100 5.6 0.63
0.690 5.0 0.91
1.500 Wilting point 4.7 0.81
1.780 4.4 0.72
Water holding capacity 11.8 0.90
(FC-WP)
1Site mean gravimetric water contents at each matric potential are presentedbecause values did not differ significantly among treatments or among blocks. Themoisture contents indicate the Aspen FACE site is a fairly uniform fine sandy loamto loam soil.
58
Table
A2
.—D
eta
iled
soi
l pro
per
ties
for
th
e A
spen
FA
CE
sit
e fo
r 1
99
7.
Va
lues
are
rin
g m
ean
s w
ith
sta
nd
ard
dev
iati
ons
liste
d in
pa
ren
thes
is
C
ontr
ol
+CO
2 +
0 3
+C
O2,
+0 3
Trea
tmen
t rin
g1,
12,
13,
11,
22,
23,
21,
32,
33,
3 1
,42,
43,
4
ME
AN
n
Soi
l tex
ture
%
san
d52
.953
.259
.351
.156
.354
.357
.956
.560
.557
.355
.951
.755
.612
(2.9
9)
%
silt
39.0
36.5
32.8
40.4
36.5
36.4
36.9
37.9
31.0
34.8
37.2
40.1
36.6
12(2
.79)
%
cla
y8.
010
.37.
98.
57.
39.
45.
15.
58.
57.
96.
98.
27.
812
(1.5
2)
Gra
vim
etric
moi
stur
e co
nten
t
θ (-
0.3
bar)
0.17
80.
172
0.13
80.
196
0.15
40.
164
0.15
10.
167
0.15
90.
158
0.16
60.
176
0.16
412
(0.0
15)
θ
(-15
bar
)0.
066
0.05
80.
057
0.08
30.
060
0.05
60.
050
0.06
90.
059
0.05
00.
051
0.05
80.
059
12(0
.010
)
θ
(WH
C)
0.11
20.
114
0.08
10.
113
0.09
40.
108
0.10
10.
098
0.10
00.
108
0.11
50.
118
0.10
413
(0.0
11)
Db
(Mg/
m3 )
1.25
1.16
1.40
1.21
1.32
1.38
1.41
1.28
1.26
1.52
1.41
1.37
1.31
120
(0.1
14)
(0.1
04)
(0.0
59)
(0.0
90)
(0.1
20)
(0.1
05)
(0.1
34)
(0.0
73)
(0.1
79)
(0.0
96)
(0.0
43)
(0.1
03)
(0.1
41)
pH5.
765.
475.
255.
735.
425.
205.
945.
795.
006.
135.
645.
165.
5559
(0.1
89)
(0.0
90)
(0.1
80)
(0.2
27)
(1.0
04)
(0.1
00)
(0.1
81)
(0.0
83)
(0.5
52)
(0.1
35)
(0.1
61)
(0.1
60)
(0.4
67)
NH
4+ -N
(µg
N/g
)1.
990.
710.
401.
231.
090.
491.
060.
620.
880.
500.
590.
600.
8560
(0.5
16)
(0.1
73)
(0.1
15)
(0.2
52)
(0.4
63)
(0.2
17)
(0.3
15)
(0.0
87)
(0.2
67)
(0.1
69)
(0.1
88)
(0.2
64)
(0.5
01)
NO
3- -N (µg
N/g
)12
.26
14.4
718
.44
16.8
716
.97
11.8
612
.27
8.97
14.2
37.
746.
4721
.73
13.5
260
(4.5
36)
(10.
843)
(17.
076)
(2.2
24)
(4.1
16)
(4.1
27)
(6.3
59)
(2.9
51)
(5.9
67)
(1.4
54)
(4.5
71)
(23.
643)
(9.8
04)
Ext
ract
able
P16
1.22
103.
8010
7.52
175.
5414
4.06
144.
4314
1.12
124.
6313
1.54
149.
2212
2.38
136.
2213
6.81
60
(µg
P/g
)(8
.965
)(7
.939
)(6
.983
)(2
2.36
1)(1
4.51
3)(2
0.05
3)(1
0.52
8)(5
.206
)(3
7.95
9)(1
2.95
2)(1
.289
)(2
0.74
7)(2
5.20
8)
Tota
l C (
%)
1.79
1.56
1.27
2.09
1.46
1.48
1.24
1.80
1.77
1.11
51.
231.
551.
5359
(0.2
29)
(0.1
20)
(0.1
14)
(0.1
04)
(0.0
94)
(0.1
83)
(0.1
11)
(0.1
98)
(0.2
44)
(0.1
11)
(0.0
58)
(0.1
01)
(0.3
08)
Tota
l N (
%)
0.13
0.12
0.11
0.17
0.11
0.12
0.09
0.14
0.14
0.08
0.10
0.12
0.12
59(0
.017
)(0
.008
)(0
.009
)(0
.008
)(0
.007
)(0
.015
)(0
.008
)(0
.015
)(0
.019
)(0
.008
)(0
.003
)(0
.013
)(0
.025
)
(tab
le A
2 co
ntin
ued
on n
ext p
age)
59
(tab
le A
2 co
ntin
ued)
C
ontr
ol
+CO
2 +
0 3
+C
O2,
+0 3
Trea
tmen
t rin
g1,
12,
13,
11,
22,
23,
21,
32,
33,
3 1
,42,
43,
4
ME
AN
n
C:N
13.4
913
.28
11.8
612
.29
12.9
012
.01
14.4
213
.23
12.9
613
.63
12.4
012
.49
12.4
959
(0.2
09)
(0.2
13)
(0.2
69)
(0.2
09)
(0.1
97)
(0.2
55)
(0.3
02)
(0.1
63)
(0.2
94)
(0.0
50)
(0.2
40)
(0.5
01)
(0.7
63)
Ca2+
0.18
0.13
n/d
0.59
0.09
0.10
0.08
0.01
0.08
0.20
n/d
0.25
0.14
60 (
cmol
(+)/
kg)
(0.1
20)
(0.0
73)
(0.0
76)
(0.0
81)
(0.0
85)
(0.0
63)
(0.0
20)
(0.0
68)
(0.0
35)
(0.0
83)
(0.1
67)
Mg2+
0.16
0.10
0.07
0.23
0.14
0.08
0.12
0.14
0.11
0.16
0.10
0.08
0.12
60 (
cmol
(+)/
kg)
(0.0
74)
(0.0
14)
(0.0
18)
(0.0
33)
(0.0
09)
(0.0
08)
(0.0
20)
(0.0
11)
(0.0
19)
(0.0
22)
(0.0
09)
(0.0
16)
(0.0
50)
K+
0.05
0.04
0.02
0.07
0.04
0.05
0.04
0.04
0.05
0.04
0.02
0.04
0.04
60(c
mol
(+)/
kg)
(0.0
16)
(0.0
10)
(0.0
10)
(0.0
10)
(0.0
10)
(0.0
09)
(0.0
04)
(0.0
11)
(0.0
10)
(0.0
03)
(0.0
05)
(0.0
09)
(0.0
16)
NH
4+0.
010.
09<
0.01
0.01
0.01
<0.
010.
01<
0.01
0.01
<0.
01<
0.01
<0.
010.
0160
(cm
ol(+
)/kg
)(0
.004
)(0
.001
)(0
.001
)(0
.002
)(0
.003
)(0
.002
)(0
.002
)(0
.001
)(0
.002
)(0
.001
)(0
.001
)(0
.002
)(0
.004
)
Exc
hang
eabl
eba
ses
0.41
0.27
0.10
0.89
0.27
0.23
0.25
0.20
0.25
0.40
0.12
0.38
0.31
60(c
mol
(+)/
kg)
(0.2
00)
(0.0
86)
(0.0
28)
(0.0
92)
(0.0
85)
(0.0
89)
(0.0
84)
(0.0
34)
(0.0
84)
(0.0
34)
(0.0
14)
(0.1
03)
(0.2
16)
Exc
hang
eabl
eac
idity
0.18
0.27
0.42
0.07
0.17
0.42
0.19
0.11
0.17
0.10
0.16
0.43
0.22
60(c
mol
(+)/
kg)
(0.0
94)
(0.0
82)
(0.1
80)
(0.0
42)
(0.0
56)
(0.0
49)
(0.0
67)
(0.0
66)
(0.0
89)
(0.0
64)
(0.1
16)
(0.1
41)
(0.1
51)
Cat
ion
exch
ange
capa
city
0.59
0.54
0.51
0.96
0.45
0.64
0.43
0.31
0.43
0.50
0.28
0.82
0.54
60(c
mol
(+)/
kg)
(0.1
43)
(0.1
06)
(0.1
63)
(0.1
21)
(0.0
95)
(0.1
00)
(0.0
87)
(0.0
68)
(0.0
63)
(0.0
69)
(0.1
12)
(0.0
88)
(0.2
12)
% b
ase
66.5
850
.51
20.9
592
.97
60.3
034
.63
56.5
267
.46
60.4
580
.14
52.2
047
.45
57.5
160
satu
ratio
n(1
8.45
4)(1
2.80
1)(1
0.09
7)(3
.270
)(1
0.56
2)(9
.419
)(1
5.45
3)(1
7.35
6)(1
8.86
5)(1
0.02
6)(2
9.64
8)(1
3.20
8)(2
3.10
7)
On
July
22,
199
7, 1
0 so
il sa
mpl
es w
ere
colle
cted
per
rin
g us
ing
rand
om a
zim
uths
and
dis
tanc
es fr
om th
e ce
nter
. S
oils
wer
e co
llect
ed to
a d
epth
of 1
0 cm
usin
g a
3.27
cm
dia
met
er c
ore
(vol
= 2
18.1
3 cm
3 ).
Sam
ples
wer
e pa
cked
on
ice,
and
ret
urne
d fo
r an
alys
is a
t Uni
vers
ity o
f Mic
higa
n’s
Terr
estr
ial E
cosy
stem
Labo
rato
ry.
Soi
l cor
es w
ere
wei
ghed
and
sub
sam
ples
wer
e ov
en-d
ried
for
dete
rmin
atio
n of
bul
k de
nsity
. P
airs
of c
ores
from
eac
h rin
g w
ere
com
posi
ted
toyi
eld
5 sa
mpl
es p
er r
ing.
Sub
sam
ples
wer
e us
ed fo
r m
easu
rem
ent o
f pH
(1:
2 so
il:de
ioni
zed
wat
er),
KC
1-ex
trac
tabl
e am
mon
ium
and
nitr
ate
(Alp
kem
RFA
300
,C
lack
amas
, OR
), d
ilute
aci
d-flu
orid
e-ex
trac
tabl
e P
(A
lpke
m R
FA 3
0), e
xcha
ngea
ble
base
s (P
erki
n-E
lmer
403
, Nor
wal
k, C
T),
exc
hang
eabl
e ac
idity
. S
oil
sam
ples
wer
e gr
ound
in a
rol
ler
mill
prio
r to
ana
lysi
s of
tota
l soi
l car
bon
and
nitr
ogen
(C
E E
lant
ech,
NA
250
0 E
lem
enta
l Ana
lyze
r, La
kew
ood,
NJ)
. S
ubsa
mpl
esof
eac
h of
the
five
sam
ples
per
rin
g w
ere
com
posi
ted
(equ
al w
eigh
t) p
rior
to d
eter
min
atio
n of
soi
l tex
ture
(hy
drom
eter
met
hod)
. S
oil m
oist
ure
deso
rptio
n cu
rves
wer
e co
nstr
ucte
d us
ing
a ce
ram
ic p
ress
ure
plat
e ex
trac
tor
(Soi
lmoi
stur
e E
quip
men
t Cor
p., S
anta
Bar
bara
, CA
).
60
Table
A3.—
Diu
rna
l oz
one
con
cen
tra
tion
s fo
r ri
ng
1,4
of
the
Asp
en F
AC
E s
ite
for
Jun
e 1
99
9 (1
-hou
r a
vera
ges
in n
ll-1)
O3
Day
day
T
ime
at th
e en
d of
hou
r (lo
cal t
ime)
avg
12
34
56
78
910
1112
1314
1516
1718
1920
2122
2324
0135
21.0
20.9
20.4
21.3
21.0
21.0
20.1
19.8
19.7
40.7
62.4
67.1
72.2
75.2
73.5
68.7
26.8
27.2
25.0
24.3
22.7
22.8
21.0
15.1
0240
11.8
11.4
10.0
9.8
10.1
11.4
13.0
20.3
41.8
54.6
60.4
66.9
70.6
74.4
74.3
75.4
75.3
72.5
69.0
43.1
35.7
28.1
16.2
7.6
0352
8.4
4.4
4.4
4.1
3.6
7.2
15.3
27.1
65.6
79.8
83.3
86.5
90.2
88.4
91.1
89.2
87.7
85.7
49.3
38.5
44.7
53.2
51.7
0459
46.2
42.8
40.6
42.8
43.4
40.0
37.7
49.4
62.7
71.4
79.3
55.4
57.8
87.4
88.5
92.0
89.4
87.9
84.1
50.4
43.4
39.1
36.1
41.5
0543
44.8
46.8
52.0
51.7
49.7
48.2
45.2
42.1
37.0
32.4
32.5
45.1
48.2
48.7
50.2
45.4
38.9
41.5
37.0
30.0
28.9
0647
32.9
38.5
35.3
37.1
35.0
36.3
34.4
32.5
30.3
31.2
31.4
33.2
78.9
88.6
88.7
91.4
84.3
47.7
43.6
42.7
41.2
41.1
38.9
35.6
0757
32.2
29.3
28.0
27.0
28.2
28.7
28.7
43.9
63.1
72.6
79.0
83.2
87.7
89.3
89.3
89.1
90.4
88.0
82.6
59.1
54.3
38.0
38.2
28.1
0851
22.5
21.6
23.3
24.7
14.9
9.3
10.8
28.8
36.4
59.9
78.4
81.6
88.8
89.5
89.3
90.9
89.7
87.5
84.2
46.9
31.4
28.9
32.1
46.8
0956
43.5
32.9
23.5
23.3
23.5
27.1
24.8
36.2
54.0
37.1
39.0
42.1
89.1
95.0
94.1
95.2
94.1
93.3
88.6
66.6
56.7
49.7
50.7
51.4
1040
53.9
48.9
41.2
32.4
20.9
27.8
29.0
30.6
36.2
37.1
39.5
57.9
94.4
52.3
38.5
40.2
38.7
38.7
38.9
34.6
31.3
28.9
28.9
26
1145
25.5
22.1
21.3
23.4
27.7
28.2
31.6
38.5
41.0
43.5
51.5
84.0
87.5
89.2
68.1
48.4
52.9
49.0
47.4
40.6
36.9
33.2
39.6
42.2
1247
39.8
29.0
24.1
23.6
23.6
23.8
22.9
24.4
47.9
64.3
71.1
77.0
78.9
85.7
85.7
84.6
83.9
82.6
77.8
40.3
18.9
13.5
8.5
5.7
1351
6.2
4.4
4.1
3.3
3.4
3.2
5.6
13.6
29.5
45.6
76.2
81.9
86.4
88.9
90.5
89.2
88.4
87.8
81.7
45.2
41.5
37.3
35.0
35.0
1433
32.8
30.7
29.1
27.7
27.3
26.5
23.9
27.6
57.9
67.8
77.6
34.8
28.8
31.9
31.6
31.6
32.2
33.0
38.1
37.3
32.0
21.9
9.9
5.1
1538
6.5
8.0
7.8
7.6
9.0
15.4
19.6
25.4
57.2
68.1
72.3
74.5
67.9
40.7
71.8
80.9
78.6
74.5
31.6
14.3
11.9
10.8
11.2
1630
9.9
10.5
9.9
9.7
9.1
13.6
20.7
22.5
27.8
26.5
54.9
76.7
83.2
68.4
36.4
36.5
35.9
36.7
37.2
35.8
20.2
13.9
8.6
6.1
1741
6.4
5.7
4.3
4.8
6.3
3.6
9.3
16.2
25.6
34.1
70.3
77.0
83.3
83.5
86.0
83.2
85.4
83.8
77.6
35.1
20.8
17.5
14.8
14.2
1848
16.1
11.7
8.6
7.9
6.3
5.4
8.9
26.0
30.4
67.0
77.0
82.6
86.6
88.3
90.4
88.6
89.7
88.0
84.6
50.3
42.6
34.0
32.2
23.6
1952
22.7
33.1
35.3
27.2
20.8
15.1
18.8
26.5
56.1
71.2
77.6
82.8
87.1
89.6
89.4
89.2
90.3
69.0
43.3
43.6
46.6
40.2
24.4
42.5
2053
48.8
46.4
44.0
30.0
34.7
34.8
30.6
27.7
33.1
28.9
32.3
37.4
45.1
79.4
90.3
90.5
89.5
89.0
86.2
69.3
47.8
46.9
55.3
56.5
2173
56.7
59.3
58.3
47.2
41.8
27.6
42.2
65.4
74.0
81.2
86.1
89.1
92.4
94.3
95.2
95.7
94.6
95.2
90.0
81.8
65.4
58.0
71.1
82.1
2281
86.2
86.8
84.9
83.8
82.0
78.0
71.3
73.9
80.9
87.2
92.2
95.3
97.6
98.8
9999
9998
.766
.962
.860
.455
.254
.752
.0
2346
51.0
47.8
45.2
47.3
46.6
44.1
48.8
46.4
45.5
51.4
53.2
54.6
71.0
52.7
51.3
48.4
46.8
46.0
45.1
37.2
33.9
28.2
26.3
27.4
2448
25.7
22.2
22.3
20.7
17.0
13.7
16.3
23.4
38.5
69.8
74.6
78.8
81.5
85.1
83.8
85.9
84.2
83.8
80.5
45.9
21.4
21.3
26.3
32.5
2552
30.8
20.8
12.3
10.5
7.9
6.4
8.9
25.8
38.7
63.5
74.8
79.1
81.9
83.9
85.5
85.4
84.0
83.3
79.6
62.1
58.2
51.7
50.9
50.2
2670
47.7
49.3
48.4
47.4
44.7
45.2
40.4
48.8
64.1
82.9
88.5
91.6
97.5
99.3
9999
9997
.694
.364
.756
.562
.155
.853
.8
2760
54.5
48.8
40.0
44.8
45.3
45.0
44.9
42.2
59.2
76.0
81.1
83.6
85.7
88.4
90.9
88.9
91.7
88.1
85.2
33.2
29.0
27.5
28.2
29.2
2836
26.5
27.1
17.8
23.5
22.1
21.8
21.7
21.1
46.8
76.2
79.7
83.3
89.4
63.4
27.4
21.7
18.9
16.5
22.0
22.4
24.2
26.5
27.5
26.9
2924
22.0
20.9
17.7
14.8
12.2
11.4
11.7
14.5
18.8
23.8
27.6
30.8
33.6
34.8
36.2
36.4
35.8
37.8
34.9
33.7
19.0
14.5
12.5
13.8
3032
13.1
12.2
6.5
9.5
11.5
16.9
29.7
29.4
50.1
75.8
30.5
31.5
59.9
31.0
34.2
38.1
38.5
39.7
39.3
33.6
27.2
32.6
37.3
38.8
47
.9 n
ll-1 is
03
aver
age
for
June
for
24 h
60
.9 n
ll-1 is
03
aver
age
for
June
for
0700
to 1
900
34
.3 µ
ll-1-h
is 0
3 S
um 0
for
June
for
24 h
21
.9 µ
ll-1-h
is 0
3 S
um 0
for
June
for
0700
to 1
900
61
Dickson, R.E.; Lewin, K.F.; Isebrands, J.G.; Coleman, M.D.; Heilman,W.E.; Riemenschneider, D.E.; Sober, J.; Host, G.E.; Zak, D.R.; Hendrey,G.R.; Pregitzer, K.S.; Karnosky, D.F.
2000. Forest atmosphere carbon transfer and storage (FACTS-II)the aspen Free-air CO2 and O3 Enrichment (FACE) project: anoverview. Gen Tech. Rep. NC-214. St. Paul, MN: U.S. Depart-ment of Agriculture, Forest Service, North Central ResearchStation. 68 p. This publication briefly reviews the impact of increasingatmospheric carbon dioxide and tropospheric ozone on globalclimate change, and the response of forest trees to these atmo-spheric pollutants and their interactions; points out the need forlarge-scale field experiments to evaluate the response of plants tothese environmental stresses; and describes the development,operational parameters, experimental methods, and the potentialresearch scope of the Aspen Free-air Carbon dioxide and ozoneEnrichment (FACE) project.
KEY WORDS: Climate change, carbon dioxide, troposphericozone, carbon sequestration, carbon-nitrogen cycles, bio-geochemical cycles, insect-disease interactions, northern hard-wood ecosystems.