seminars eecb seminar thurs 4:00 pm osn 120. dr. larry stevens, grand canyon wildlands council....
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Seminars
• EECB seminar Thurs 4:00 PM OSN 120. Dr. Larry Stevens, Grand Canyon Wildlands Council. “Biogeography of the Grand Canyon, and Colorado River Management”.
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Reading
• Textbook Chapter 12 and 13• Sparrow, A., M. Friedel, and D. Tongway.
2003. Degradation and recovery processes in arid grazing lands of central Australia part 3: implications at landscape scale. Journal of Arid environments 55: 349-360.
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Outline1. Case study: identifying communities and
relating to environmental conditions2. Student case studies3. Productivity – plants and ecosystems 4. GPP, NPP, and Efficiency5. Global and environmental patterns of
NPP6. Production in forest VS rangeland7. Factors influencing productivity – fire,
herbivory, nutrient pulses, etc.8. Climate change, CO2 accumulation, and
carbon sequestration
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Identification and interpretation of community
patterns• Using classification (TWINSPAN) to identify wet meadow communities
• Relate community classification to environmental (hydrologic and geomorphic) variables
• Interpret impact of stream incision on vegetation communities
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Humboldt-Toiyabe National ForestCentral NevadaSan Juan Creek
Reese River
Birch Creek
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Reach-scale vegetation patterns
Above-fan:Broad valley bottomWet meadows
At-fan:Narrow valley bottomWoody riparian andupland vegetation
Below-fan: Intermediatevalley characteristicsWoody riparian,mesic & dry meadows
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Objectives – Hydrologic Component
• Determine the dominant vegetation types & their species associations within Kingston Meadow
• Examine relationship of vegetation types to the current hydrologic regime within Kingston Meadow
• Evaluate any changes in vegetation associated with a different hydrologic regime following meadow restoration activities
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Sampling Scheme
Determine the composition, ground cover, and biomass of the vegetation associated with each piezometer or nested well across a hydrologic gradient within the meadow
• 14 cross-valley transects (10 with piezometers/wells; 4 more to adequately sample vegetation)
• 55 sampling points (45 nested piezometers + 10 additional sampling points)
• 110 sample plots (2 subsamples per sampling point)
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Terrace Height TWINSPAN
Vegetation Cover Class Name nBig Sagebrush/Dry Meadow 53 1.90 ± 0.18Chokecherry/Woods Rose/Willow 14 1.42 ± 0.26Western Birch/Dogwood 10 1.10 ± 0.36Aspen/Woods Rose 15 0.91 ± 0.16Mesic Meadow 12 0.87 ± 0.18Wet Meadow 23 0.50 ± 0.06Streambank (Willow/Mesic Meadow) 22 0.47 ± 0.04
Mean Terrace Height (m)
From unpublished data and Henderson, 2001Stream cross-sections
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Bea
ked
Neb
rask
a
Mes
ic
Dry
Sag
e
Wat
er T
able
Dep
th (
cm)
-300
-250
-200
-150
-100
-50
0
50
Meadow Type
Meadow GroundwaterCharacteristics
From Linnerooth & Chambers, 2000
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Vegetation Types- Hydrology Plots
Dominate SpeciesWetland Status
Present in Geomorphic
Plots
Carex rostrata Carex rostrata OBL
Carex nebrascensis Carex nebrascensis OBL
Mesic Graminiod Poa pratensis
Juncus balticus
FACU
OBL
Dry/Planted Bromus inermis
Cardex douglasii
Agropyron cristatum
NONE
FACU
NONE
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De
pth
to w
ate
r ta
ble
(cm
)
-25
0
25
50
75
100
125
150
175
aab
b
c
Carex rostratan=2
Carex nebrascensisn=14
Mesic Graminiodn=51
Dryn=12
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Hei
ght a
bove
str
eam
bed
(cm
)
0
25
50
75
100
125
150
175
200
Carex nebrascensisn=42
Mesic Graminiodn=112
Dry/Plantedn=25
a
b
b
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Current System Dynamics
• Climate changes that occurred over 2000 years ago are still influencing system dynamics
• Recent incision began at the end of the Little Ice Age about 290 years ago
• The rate and magnitude has undoubtedly been increased by human disturbance
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Stream Incision: Causes
• Overgrazing in riparian zone and upland areas within the watershed
• Roads (crossings, captures)• Sediment “starvation” due to long-term
climate effects
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Barrett CanyonCorral Canyon
Stream Incision: Causes
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Stream Incision: Causes
• Overgrazing in riparian zone and upland areas within the watershed
• Roads (crossings, captures)• Sediment “starvation” due to long-term
climate effects
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Stream Incision: Consequences
• Lowers water table in the riparian zone (threshold event)
• Stream flow becomes isolated from former floodplain
• Development of inset terraces• Invasion of more-xeric species• Narrowing of riparian zone and loss of
riparian habitat
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Barley Cr. (Monitor Range)
San Juan Cr.
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Cottonwood Creek
1994
1998
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Incising Meadow
Ground SurfaceWater Table Surface
Non-Incised Meadow
Ground SurfaceWater Table Surface
Gaining Systems
Losing Systems
Ground Surface
Water Table Surface
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Your turn…• List management issues/projects you
know of in range and forest ecosystems.
• Which of the ecological processes or interactions we have discussed so far do you need to understand?
• Can you make predictions or recommendations based on your understanding of the ecological systems?
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Productivity• Energy captured by autotrophs.• GPP=total solar radiation fixed into
chemical energy via photosynthesis• NPP=GPP-respiration• Textbook Figure 12.1 = energy pathways
at primary trophic level. Solar energy is reflected, emitted, assimilated, respired, consumed by herbivores, turned into detritus, or stored in standing crop/biomass.
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Efficiency• Proportion of energy converted into plant
material. Three components:– Exploitation efficiency = ability to intercept light.
GPP/solar radiation X 100%. Affected by LAI, leaf orientation, latitude, topographic location.
– Assimilation efficiency = ability to convert absorbed light into photosynthate. GPP/absorbed radiation X 100%. Affected by CO2 absorption, temperature, light and water availability.
– Net production efficiency = capacity to convert photosynthate into growth/reproduction rather than respiration. NPP/GPP X 100%. Depends on temperature and amount of non-photosynthetic biomass supported.
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Net Primary Production• Difficult to measure accurately on large
scale because requires measures of photosynthetic and respiration rates.
• Usually use changes in biomass over timeNPP = (wt+1- wt) +D + H
Where (wt+1- wt) is change in biomass over time
D= biomass lost to decompositionH= biomass lost to herbivores
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Net Primary Production• Can also use allometric means: changes
in plant size; use regression to assess. • Allometry provides measure of root
production (mini-rhizotron images)• Global scale
– Models based on climate, precipitation, evapotranspiration
– Also – remote sensing data
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Carbon balance
• NPP-decomposition/loss to herbivores• Essentially change in standing crop over
time• Important in assessing impact of
vegetation on CO2 emissions under Kyoto Protocol etc.
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Relationship of biomass to productivity
• BAR = biomass accumulation ratio• Ratio of dry weight biomass to annual NPP.• Higher for plant communities with more
long-lived structure (woody plants)
Plant community BAR
Annual 1
Desert 2-10
Grassland 1.3-5
Shrubland 3-12
Forest 20-50
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Forest biomass and NPP• Productivity often strongly related to soil
fertility or texture (eg N mineralization rate in eastern US)
• As community ages, ANPP changes:– Immediately following disturbance ANPP rapid and
biomass accumulates quickly– Maximum NPP and living biomass at 50-100 yrs– Leaf biomass is maximal just before canopy
closure– Older forests have lower carbon balance –
decomposition and respiration/maintenance of nonphotosynthetic tissues
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Rangeland biomass and NPP
• Higher biomass not necessarily related to higher NPP
• In dense grasslands removal of dead or “decadent” biomass may stimulate productivity
• Indication of coevolution of herbivores and grasses? Ability of grasses to re-grow photosynthetic tissue after removal = herbivore tolerance
• Grazing lawns = rapid nutrient cycling and high productivity caused by repeated grazing
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Factors affecting NPP• Light, temperature• Water (precipitation, evapotranspiration)• Carbon dioxide (high concentrations more
influential for C3 than C4)
• Nutrient availability (see handout and text P326)
• Herbivory – can stimulate (by reducing competition for light) or decrease (by removing photosynthetic tissue)
• Fire – usually stimulates: release of nutrients, removal of competition for light and water
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Variable resources• Resources are not constant in time or
space• Ecosystems are limited by a variety of
resources• Transient Maxima Hypothesis: TMH
– Explains patterns of productivity for non-equilibrium systems.
– E.g. tallgrass prairie: at equilibrium, light is limiting (soil resources not utilized to maximum)
– When disturbed, light not limiting, productivity increases to utilize available resources (hence increase in productivity with fire or herbivory)
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Global carbon cycle• Atmospheric carbon flux strongly
affected by human activity• Combustion of fossil fuels and clearing
of forest releases sequestered carbon into atmosphere
• Substantial changes in CO2 since industrial revolution (from 280 ppm to >350 ppm)
• Productivity of vegetation affects CO2
concentration in atmosphere