Land-use effects on spatial and temporal patterns of carbon storage and flux in PNW forests

David WallinDepartment of Environmental Sciences

Huxley College of the Environment

Western Washington University

Bellingham, WA

Collaborators

• Peter Homann: Dept. of Environmental Sciences, Huxley College, WWU

• Mark Harmon: Dept. of Forest Science, Oregon State University

• Warren Cohen: USDA Forest Service, PNW Research Station

• Olga Krankina: Dept. of Forest Science, Oregon State University

Why is the global carbon cycle important?

• All life on the planet is based upon the cycling of carbon

Carbon Cycling

Photosynthesis

6CO2 + 12H20 Life 6O2 + C6H12O6 + 6H20

Respiration

Photosynthesis and respiration are among the most important mechanisms controlling the global carbon cycle

Plants use CO2 from the atmosphere as a source of both C and O for the production of glucose (C6H12O6), with H20 providing the necessary H

Carbon Cycling

Glucose (C6H12O6) is the central carbohydrate compound of protoplasm, and carbohydrates constitute a large percentage of the total dry biomass of plants. Glucose is composed of:

6 atoms of C; atomic wt = 12 72

6 atoms of O; atomic wt = 16 96

12 atoms of H; atomic wt = 1 12 ----

180

So, (72 + 96)/180 = 0.93

93% of the mass of the glucose molecule is derived directly from air!

Carbon Cycling

Plants, and animals, are composed of more than just C, O, and H; other important elements include N, P and K.

Nevertheless, about half of the dry biomass of plants is composed of C and this C is derived entirely from the atmosphere.

Why is the global carbon cycle important?

• All life on the planet is based upon the cycling of carbon

• Atmospheric concentrations of CO2 have increased substantially over the past century or so, largely as a result of the combustion of fossil fuels

Long-term variation in atmospheric CO2 concentrations: The Vostok ice core

Recent trends in atmospheric CO2 concentrations: The role of fossil fuel burning

Even more recent records reveal that atmospheric CO2 concentrations continue to increase

Why is the global carbon cycle important?

• All life on the planet is based upon the cycling of carbon

• Atmospheric concentrations of CO2 have increased substantially over the past century or so, largely as a result of the combustion of fossil fuels

• CO2 is a “greenhouse gas” and, as such, increasing atmospheric concentrations of CO2 have the potential to cause major changes in the earth’s climate

A “Greenhouse Gas”; What does this mean?

• I. The Electromagnetic Spectrum

A “Greenhouse Gas”; What does this mean?

• II. Sources of EM Energy– The amount of energy emitted by an object (area under the

curve) and the wavelength of peak emission area function of the temperature of the object

A “Greenhouse Gas”; What does this mean?

• III. Interaction of EM energy with solids, liquids and gasses

A “Greenhouse Gas”; What does this mean?

• IV. Greenhouse gasses absorb EM energy very strongly at wavelengths (8-10 um) where the earth is emitting EM energy to space. This results in a warming of the atmosphere.

Major reservoirs in the global carbon cycle

Atmosphere 748 PgTerrestrial 2,000 PgOceans 38,000 PgGeologic 4,000 Pg

The geologic stores of recoverable fossil fuels were arelatively inactive reservoir in the global carbon cycle prior to the industrial revolution.

Pg = 1015 grams

Sources and Sinks in the global carbon budget: 1980-1995

Fossil fuel combustion 5.7 Pg C/yrLand-use emissions 1.9 Pg C/yrOceans -2.1 Pg C/yrAtmosphere -3.2 Pg C/yr

“The Missing Sink” 2.3 Pg C/yr

Houghton 2000 J. Geophys. Res. 105:20121-20130

Northern Hemisphere, Mid-latitude Forests: The Missing Sink?

• YES: Based on Atmospheric models that infer the combination of sources and sinks in atmospheric transport models that best match the global atmospheric CO2 data

• NO: Most land-based approaches using inventory data and ecosystem models have not been consistent with predictions, however, these studies have revealed significant heterogeneity in both space and time for terrestrial C pools and fluxes. These results have pointed to the need for more careful regional-scale analyses of C pools and fluxes.

• MAYBE (…Probably?…): Most recent results for the coterminous U.S. (Pacala et al. Science 292:2316) are consistent with the atmospheric studies, suggesting a net sink of 0.3-0.58 Pg C/yr (0.39-0.76 Mg C/ha/yr).

Regional-scale analyses are needed

• Analyses at the global and continental scale mask spatial and temporal heterogeneity in terrestrial C pools and fluxes

• An understanding of this heterogeneity is needed to narrow the remaining uncertainty in the global C budget.

• An understanding of this heterogeneity may reveal opportunities for management action that could increase C storage in terrestrial systems.

Land-use Impacts on PNW Forests

• PNW forests are among the most productive in the world.

• These forests have the capacity to store significant amounts of C

• Timber harvest activities in this region have the capacity to have a major impact on C flux.

Recent changes in harvest rates

0

2

4

6

8

10

1960 1970 1980 1990 2000

Year

Har

vest

Vo

lum

e (B

illio

ns

of

Bo

ard

F

eet

per

Yea

r)

TotalBLM + USFSIndustryOther

Or. Dept. Forestry Harvest Stats.

Westside Timber Harvest in Oregon

Disturbed Forest Carbon Model

Atmosphere

Onsite -Living -Detrital

Offsite -Forest Products

Harmon et al. 1990. Science 247:669

LANDCARB: A landscape-level carbon model

• Quantifying carbon dynamics at the landscape and regional scale requires the use of a model that captures the spatial and temporal complexities in terrestrial systems

• Satellite data can provide information on spatial and temporal heterogeneity

• A detailed stand-level model (STANDCARB) is used to parameterize a simplified “metamodel” that can be applied to individual grid cells corresponding to the ground resolution of the satellite imagery.

Carbon Storage following the disturbance of an old-growth stand

0

100

200

300

400

500

600

-50 50 150 250 350 450

Year

Car

bo

n S

tora

ge

(Mg

C/h

a)

Total

Live

Dead

Forest Products

Site Index 3

Overall Carbon flux from Western Oregon: 1972-95

A net SOURCE for 0.68 Mg C/ha/yr during 1972-95

Carbon Flux From Western Oregon: 1972-95

-2

-1

0

1

2

3

Year Intervals

C F

lux

(M

g C

/ha

/yr)

LiveDeadFor ProdTotal

Source to Atmosphere

Sink from Atmosphere

1972-77 1977-84 1984-88 1988-91 1991-95 1972-95

Range of variation in carbon flux

Total Carbon Flux from W. Oregon: 1972-95

0

5

10

15

20

25

30

35

-5 to -4 -4 to -2 -2 to -0.25

-0.25 to0.25

0.25 to2

2 to 4 4 to 8 8 to 14

Mg C / ha / yr

% o

f F

ore

st A

rea Sink from Atmosphere Source to Atmosphere

Model Validation

Total Harvest Volume (Tg C) 1972-95: Oregon Department of Forestry Records vs. LANDCARB Model Estimates. Each point represents a single county.

y = 0.80x - 0.17

0

10

20

30

40

0 5 10 15 20 25 30 35 40

Oregon Department of Forestry Records (Tg C)

LA

ND

CA

RB

Mo

de

l E

sti

ma

tes

(T

g C

)

Source for 0.68 Mg C/ha/yr

Sink for 1.24 Mg C/ha/yr

“What If” No timber harvests conducted from 1972-95?

Carbon Budget: Western Oregon, 1972-95

-4

-3

-2

-1

0

1

2

3

Year Intervals

Ca

rbo

n F

lux

(M

g/h

a/y

r)

Live

Dead

Offsite

Total

"What If" No timber harvest conducted from 1972-95

1972-77 1977-84 1984-88 1988-91 1991-95 1972-95

Source to Atmosphere

Sink from Atmosphere

A net SINK for 1.24 Mg C/ha/yr during 1972-95

Effect of Rotation Length on Carbon Storage

100

200

300

400

500

600

-50 50 150 250 350 450

Year

To

tal

C S

tora

ge

(M

g C

/ha

)

One harvest

100 Yr. rotation harvest

50 Yr. rotation harvestfirst harvest

Summary• Over the past 23 years, the forests of Western Oregon have been a net

source for 0.68 Mg C/ha/yr• Across the study area, C flux ranged from a sink of 4.7 to a source of

13.2 Mg C/ha/yr• This variability was related to land-use history, ownership and site

conditions• In the absence of timber harvesting between 1972 and 1995, this area

would have been a net sink for 1.24 Mg C/ha/yr• Our results demonstrate that timber harvesting has had a major impact

on the regional carbon budget and that changes in timber management practices could result in the sequestration of significant amounts of carbon in the region