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Effects of Land Use Change on Forest Carbon Budgets Throughout the Southern USA from 1900 to 2050
Peter B. WoodburyCrop and Soil Sciences Department, Cornell University
James E. Smith, and Linda S. HeathUSDA Forest Service, Durham, NH
Third USDA Symposium on Greenhouse Gases and Carbon Sequestration in Agriculture and Forestry
March 22-24, 2005, Baltimore, Maryland
Goal: Improve US national estimates of terrestrial carbon flux from the forest sector.
Such estimates needed annually for the US Greenhouse Gas Inventory required under the United Nations Framework Convention on Climate Change (UNFCCC). The UNFCCC reporting period begins in 1990.
Land Use Transitions:Land Use Transitions:Model focuses on afforestation and deforestationModel focuses on afforestation and deforestation
Forest
Pasture/Grassland
Urban/Developed
PlowedCropland
Forest Carbon Pools
Down dead woodDown dead wood
UnderstoryUnderstory
Live Live treestrees
Standing Standing dead dead treestrees
Soil organic Soil organic carbon (to 1 m)carbon (to 1 m)
Forest floorForest floor
How to estimate land use change How to estimate land use change effects on forest carbon cycling? effects on forest carbon cycling?
For tree and down dead wood pools, use forest inventory (FIA) data and FORCARB model (see talks by James Smith and by Linda Heath this afternoon)
For soil and forest floor, we developed a model to predict effects from 1900 to 2050.
1) Quantify land use transition rates (based on work by R. Birdsey)
2) Develop equations to predict effect of each land use transition on soil and forest floor carbon.
Model Regions: For today, South-Central Model Regions: For today, South-Central and Southeast regionsand Southeast regions
Key model inputsKey model inputs
Historical land use transition matrix:
Forest inventory data and reports, National Resource Inventory data, and Census of Agriculture.
Soil and forest floor carbon density for each land use and each forest type:
Soil from STATSGO soil database, overlaid with forest type groups, from Johnson and Kern 2003.
Forest floor, from Smith and Heath 2002.
Land Use Transition Example: Land Use Transition Example: Historical afforestation and deforestation in South-CentralHistorical afforestation and deforestation in South-Central
-6000
-5000
-4000
-3000
-2000
-1000
0
1000
2000
3000
4000
1900 1925 1950 1975 2000
Year
An
nu
al A
rea
Ch
an
ge
(1
00
0 h
a)
Total Defor.
Total Affor.
Pine Defor.
Pine Affor.
Key Model EquationsKey Model Equations
Afforestation effects on soil carbon
Deforestation effects on soil carbon
Afforestation effects on forest floor carbon
Deforestation effects on forest floor carbon
Change in soil carbon after afforestation for Loblolly pine forest type
Woodbury et al. draft May 2004
0102030405060708090
100
0 25 50 75 100 125 150 175 200Years Since Land Use Change
So
il C
to
1 m
Dep
th (
t/h
a)
-20
-15
-10
-5
0
5
10
15
20
0 10 20 30 40 50
Years Since Land Use Change
Car
bon
Flu
x fr
om F
ores
t F
loor
(t/
ha)
Afforestation (negative)
Deforestation (positive)
Changes in forest floor carbon for pine forest typesChanges in forest floor carbon for pine forest types
Based on Smith and Heath 2002
RESULTS: Effects of afforestation are damped and RESULTS: Effects of afforestation are damped and lagged, for example in the South-Central regionlagged, for example in the South-Central region
-6
-5
-4
-3
-2
-1
0
1900 1925 1950 1975 2000 2025 2050Year
An
nu
al C
ha
ng
e in
C S
toc
ks
(T
g/Y
)
-600
-500
-400
-300
-200
-100
0A
nn
ua
l Are
a A
ffore
ste
d
In Southeast, net emission until 1940’s, then generally sequestration
Woodbury et al. draft June 2004
-300
-200
-100
0
100
200
300
1900 1925 1950 1975 2000 2025 2050Year
Cu
mu
lati
ve
Ch
an
ge
in C
Sto
ck
s (
Tg
)
Forest Floor
Forest Floor
Soil
Soil
TOTAL
In South-Central, greater effects with later peak
Woodbury et al. draft June 2004
-300
-200
-100
0
100
200
300
1900 1925 1950 1975 2000 2025 2050Year
Cu
mu
lati
ve
Ch
an
ge
in C
Sto
ck
s (
Tg
)
Forest Floor
Forest Floor
Soil
Soil
TOTAL
Down dead woodDown dead wood
UnderstoryUnderstory
Live Live treestrees
Standing Standing dead dead treestrees
Soil organic Soil organic carbon (1m)carbon (1m)
Forest floorForest floor
But wait, But wait, soil and forest floor are only part of the story!soil and forest floor are only part of the story!
From 1990 to 2004, sequestration in trees in Southern US From 1990 to 2004, sequestration in trees in Southern US was 6-fold greater than that in soil and forest floorwas 6-fold greater than that in soil and forest floor
-300
-250
-200
-150
-100
-50
0
50
100
Tre
es
So
ila
nd
Fo
r.F
loo
rTo
tal C
ha
ng
e in
Ca
rbo
n (
Tg
)
-39-240
ConclusionsConclusions
From 1900 to 1990, land use change in the Southern US caused net carbon emission of 270 Tg C from soil and forest floor.
Conversely, from 1990 to the present, land use change caused net carbon sequestration of 39 Tg C.
Changes in forest floor carbon were similar to changes in soil carbon, despite much less total carbon.
Changes in tree carbon stocks during this period were 6-fold greater than effects on soil and forest floor carbon stocks.
Therefore, estimates of forest carbon sequestration are dominated by effects on tree carbon stocks, which can be estimated based on forest inventory data.
AcknowledgementsAcknowledgements
Rich Birdsey, USDA Forest Service, PA
Jeff Kern & Mark Johnson, USEPA, OR
Steve Prisley & Beyhan Amichev, Virginia Tech, VA
Mike Nichols, USDA Forest Service, NH
Ken Skog, USDA Forest Service, WI
Tom Wirth, USEPA, Washington D.C.
Funding provided by
USEPA and the USDA Forest Service
Draft results for all regions of USADraft results for all regions of USA
-400
-300
-200
-100
0
100
200
300
400
500
600
1900 1925 1950 1975 2000 2025 2050
Year
Cum
ulat
ive
Cha
nge
in C
Sto
cks
(Tg)
TOTAL
SE
NE
PC
GP
SCRMNC
Why model land use change effects?
Land use change is an important type of global change in its own right!
Land use change affects terrestrial carbon flux, and may also affect climate.
Our immediate goal: Improve US national estimates of terrestrial carbon flux, with a focus on forests.
Such estimates needed annually for the US Greenhouse Gas Inventory required under the United Nations Framework Convention on Climate Change (UNFCCC).
Main data sources for estimating land use Main data sources for estimating land use transitionstransitions
National Resource Inventory (measures actual transitions on survey plots, only started 20 years ago, doesn’t cover all lands).
Forest Inventory data (systematic surveys since about 1935)
Forest survey reports (used for early 1900s)
Census of Agriculture (used for early 1900s)
Model Parameter Example:Model Parameter Example:
Forest soil carbon density values derived from STATSGO Forest soil carbon density values derived from STATSGO
0
50
100
150
200
250
Oak-p
ine
Oak-h
ickor
y
Loblol
ly-sh
ortle
af p
ine
Map
le-bee
ch-b
irch
Oak-g
um-cy
press
Spruce
-fir
Aspen
-birc
h
Soi
l Car
bon
Den
sity
(t/
ha,
1 m
dep
th)
Just a little jargon …
AFFORESTATION: Conversion of land that has been non-forested for 20-50 years into forest.
REFORESTATION: Growth of forest on previously forested land (not considered a land use change in our model).
DEFORESTATION: Conversion of forest to another land use.
FOREST FLOOR: All material above the mineral soil, including woody material < 7.5 cm in diameter.
FOREST TYPE: A broad classification of forests by dominant species, from USDA Forest Service (for example “Maple/Beech/Birch”.
Change in Soil Carbon with DeforestationChange in Soil Carbon with Deforestation
-80
-60
-40
-20
0
20
40
0 5 10 15 20 25 30 35 40 45 50 55
Years after Deforestation
Ch
ange
in S
oil C
(%
)
Houghton and Hackler (2001)
Murty et al. 2002
FORLUCModel
Test of Forest Floor Model:
Change in forest floor carbon with replacement of a 55 y old
mixed conifer / hardwood stand with a loblolly pine plantation
0
5
10
15
20
25
30
35
0 5 10 15 20
Years Since Land Use Change
For
est
Flo
or C
(t/
ha)
Model (Smith & Heath 2002)
Key Model CalculationsKey Model Calculations
All calculations are by region, by forest type, and by “cohort” (cell in the transition matrix).
For each time period, calculate:
Effect of each land use transition on soil carbon flux.
Effect of each land use transition on forest floor carbon flux.
Store results for each “cohort” for each time period, generate graphs and tables.
How we estimate forest and wood carbon stocksHow we estimate forest and wood carbon stocks
FIA data, volume-biomass Tree carbon, equations in the past
ATLAS and FORCARB Tree carbon, Future forests models present, future
Soil survey data, land use Soil carbon model (FIA P3, coming soon!)
Intensive research site data and models Forest floor, (FIA P3, coming soon!) Down dead,
Understory
Tree Carbon Density in 2002 (t/ha)
Woodbury et al. 2004 (in US Greenhouse Gas Inventory
Annual Change in Tree Carbon in 2002 (t/ha)
Based on Woodbury et al. 2004 (in US Greenhouse Gas Inventory)
Estimating changes in forest carbonEstimating changes in forest carbon(stock change approach)(stock change approach)
Estimate forest carbon at Time 1 = C1
Estimate forest carbon at Time 2 = C2
Annual change = (C2 – C1) / years
Land use change effects during the UNFCCC reporting period Land use change effects during the UNFCCC reporting period are very different than effects over the last centuryare very different than effects over the last century
-1500
-1000
-500
0
500
1000
1500
2000
FO
RL
UC
1990
to
2004
FO
RL
UC
19
00 t
o 20
04
Tot
al C
han
ge in
C (
Tg)
Ove
r P
erio
d
-58 299
Soil
ForestFloor
A CONCLUSION: Sequestration in the rest of the forest A CONCLUSION: Sequestration in the rest of the forest sector is much greater than that in soil and forest floorsector is much greater than that in soil and forest floor
-3500
-3000
-2500
-2000
-1500
-1000
-500
0
500
US
GH
G19
90 t
o 20
04
FO
RL
UC
1990
to
2004
Source of Estimate
Tot
al C
han
ge in
C (
Tg)
Ove
r P
erio
d
Soil
ForestFloor
Tree
HarvestedWood
Down Woody Debris
Soil
ForestFloor
Some Key AssumptionsSome Key Assumptions
Because the model focuses on transitions to and from forest, not all lands and land use changes are modeled.
All land throughout a large region is assumed to respond in the same way to land use changes.
All carbon lost from forest soil and forest floor is emitted to the atmosphere. For example, no carbon is assumed to be stored in sediments.
More Key AssumptionsMore Key Assumptions
There is no net change in soil carbon due to transitions between forest and pasture, but there is loss of forest floor carbon.
Disturbances such as fire are not explicitly included in the model except as they are captured by differences in soil and forest floor carbon between land use types.
Changes in soil bulk density are not explicitly accounted for, but the parameter selected for the total change in soil carbon with deforestation implicitly accounts for higher bulk density in agricultural than in forest soils.
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