Transcript Biospheric Process Models: The Challenge of Integrating Ecosystem Dynamics and Land Cover Change A.

Biospheric Process Models:
The Challenge of Integrating Ecosystem
Dynamics and Land Cover Change
A. David McGuire
USGS and University of Alaska
Historically Two Approaches
Landuse
and
Disturbance
CO2 and Climate
Book-keeping
Models
Process-Based
Ecosystem
Models
Modeling Integration for Investigating
Global Change in Terrestrial Ecosystems
CLIMATE
Physical
Properties
Ecosystem
Structure
Ecosystem
Function
DISTURBANCE
Human
Dimensions
Process Models and Atmospheric Constraints
McGuire and CCMLP Participants. 2001. Carbon balance of the terrestrial
biosphere in the twentieth century: Analyses of CO2, climate and land use
effects with four process-based ecosystem models. 2001. Global
Biogeochemical Cycles 15:183-206.
Dargaville and CCMLP Participants 2002. Evaluation of terrestrial carbon
cycle models with atmospheric CO2 measurements: Results from
transient simulations considering increasing CO2, climate, and land-use
effects. Global Biogeochemical Cycles 16, 1092,
doi:10.1029/2001GB001426.
Dargaville, R., A.D. McGuire, and P. Rayner. 2002. Estimates of large-scale
fluxes in high latitudes from terrestrial biosphere models and an inversion
of atmospheric CO2 measurements. Climatic Change 55:273-285.
Goal of Study:
… to simulate the concurrent effects
of cropland establishment and
abandonment, increases in
atmospheric CO2, and interannual
climate variability on terrestrial
carbon storage between 1920 and
1992.
NET
CO2
Concentration
Climate
(Temperature,
Precipitation)
Landuse
Map
NPP
RH
Conversion
Flux
Fire
Disturbance
TBM
Carbon
Pools
Product
Decay
Flux
1 yr
10 yr
100 yr
Product Pools
Simulating the Effects of CO2, Climate, and
Cropland Establishment and Abandonment by
Terrestrial Biosphere Models (TBMs)
Driving Data Sets
Historical CO2: based on Etheridge et al. (1996) and Keeling et al. (1995)
Temperature: based on Cramer and Leemans climatology and Jones
et al. (1994) temperature anomalies
Precipitation: based on Cramer and Leemans climatology and Hulme
et al. (1992, 1994, updated) precipitation anomalies
Solar Radiation: based on Cramer and Leemans climatology
Historical Landuse: based on Ramankutty and Foley (1998)
Relative Agricultural Productivity: based on Esser (1990)
Other Data Sets: vegetation and soils - model specific
Comparison between net fluxes simulated
by terrestrial biosphere models with a longterm inversion analysis of terrestrial C
exchange with the atmosphere
CO2/O2 Budgets
Net Biota-to-Air
HRBM
IBIS
LPJ
TEM
S3 Net Flux (Pg C yr-1)
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
1920
1930
1940
1950
1960
1970
1980
1990
2000
Modeled terrestrial exchange is consistent (within the
uncertainty) with the long-term inversion analysis.
Partitioning effects of CO2, climate, and cropland establishment and
abandonment on global terrestrial carbon storage for HRBM,IBIS,LPJ and TEM
The models indicate that the effects of CO2 and cropland
establishment/abandonment play important roles in terrestrial carbon
storage. The models agree that the effects of climate are small relative
to the effects of CO2 and land use, but disagree about whether climate
variability tends to cause net uptake or release of CO2.
Mean Annual Net Carbon Exchange for the 1980s
(CO2, Climate, and Land Use)
HRBM
IBIS
LPJ
TEM
gC m2 yr1
-1000
-10
-1 1
10
100
1000
Mean Annual Net Carbon Exchange for the 1980s
(Land Use)
HRBM
IBIS
LPJ
TEM
gC m2 yr1
-1000
-10
-1 1
10
100 1000
Regional Changes in Carbon Storage may be
Caused by Responses that affect Ecosystem
Physiology, Disturbance, and Land Cover Change
McGuire et al. 2004. Canada and Alaska.
Csiszar, I., et al. 2004. Land use and fires.
Chapters 9 and 19 in Land Change Science: Observing, Monitoring, and
Understanding Trajectories of Change on the Earth’s Surface. Dordrecht,
Netherlands,
Kluwer Academic Publishers.
Zhuang et al. 2003. Carbon cycling in extratropical terrestrial ecosystems
of the Northern Hemisphere during the 20th Century: A modeling analysis
of the influences of soil thermal dynamics. Tellus 55B:751-776.
McGuire et al. 2002. Environmental variation, vegetation distribution,
carbon dynamics, and water/energy exchange in high latitudes. Journal of
Vegetation Science 13:301-314.
Biomass of Boreal Forest Ecosystems
has been Changing in Recent Decades
From Myneni et al. (2001)
Growing seasons are occurring earlier
Courtesy of K. McDonald
Duration of Snow Free
Period 1972-2000
8.0 –18.0 Weeks – Region 1
18.0 – 28.0 Weeks – Region 2
28.0 –37.0 Weeks – Region 3
1
Region 1
0.5
0
-0.5
-1
Slope = 0.035 Intercept = -0.499
R2 = 0.22
-1.5
1999
1996
1993
1990
1987
1984
1981
1978
1975
1972
-2
Weeks of Snow Free Duration (1972-2000)
Region 1
Region 2
Based
on TEM
simulation
for north of
30o N
Region 3
Mean
SD
CV
TEM
14.1
3.5
0.24
Dye*
14.3
1.4
0.10
TEM
23.3
2.1
0.09
Dye
23.1
1.2
0.05
TEM
30.2
0.7
0.02
Dye
30.9
1.0
0.03
*D. Dye, Hydrol. Process., 2002
Strategy to evaluate seasonal exchange of carbon
dioxide simulated by terrestrial biosphere models
Observed and simulated atmospheric CO2
concentrations at Mould Bay Station, Canada
(-119.35oW, 76.25oN) during the 1980s
Spatial patterns of change in vegetation carbon over the twenty year period spanning
from 1980-2000 as simulated by the Terrestrial Ecosystem Model (TEM)
90°
60°
30°
-75
-60
-45
Sink
-30
-15
0
10
25
g C m-2 yr-1
Source
Incorporation of freeze-thaw dynamics into the Terrestrial Ecosystem model improves the simulation
of the seasonal and decadal exchange of carbon dioxide exchange with the atmosphere
(Zhuang, Euskirchen, McGuire, Melillo, Romanovsky)
After crown fires, boreal conifer forests are often
replaced by less flammable deciduous broad-leaved vegetation
Fire in Canada has became more frequent after 1970
NCE
[CO2] and [O3]
and N
Deposition
NPP
RH
Fire Emissions
Climate
(Temperature,
Precipitation)
Fire regime
(Severity,
History)
TEM
Carbon
Pools
Simulation of the effects of changes in [CO2], [O3], N deposition,
Climate, and Disturbance by the Terrestrial Ecosystem Model (TEM)
Firescars and Cohorts
Long-term Fire Return Interval for Alaska
Cumulative Changes in Carbon Stocks for Alaska
from 1950 - 1995
Uptake
1000
PFRI* = 50% FRI
PFRI = 100% FRI
PFRI = 150% FRI
800
* Pre-historical Fire Return Interval (before 1950)
Tg
600
** Fire Return Interval (1950-1995)
400
200
0
1950
1955
-200
Release
JSC 7/23/02
1960
1965
1970
1975
1980
1985
1990
1995
Stand Age
19
17
15
13
11
9
9
9
9
9
99
+
99
99
79
59
39
0
-2
-1
-1
-1
-1
30
9
9
9
9
9
9
9
19
-9
-8
-7
-6
-5
-4
-3
9
9
-2
-1
-9
-1
89
79
69
59
49
39
29
19
10
0
Percent of Total Area of Interior Alaska
Forested Area by Age Category
25
Estimate from Forest Inventory Data
20
TEM 55% Fire Return Interval
15
10
5
0
Cumulative Changes in Carbon Stocks
in Alaska and Canada, 1960 to 1995
2000
CO2
CO2 + Climate
1500
CO2 + Climate + Fire
CO2 + Climate + Fire +O3
Tg C
CO2 + Climate + Fire + O3 +Ndep
1000
500
0
1960
1970
1980
1990
2000
The high latitude transects
span significant variation
in several environmental
variables and provide a
network for improving our
understanding of controls
over vegetation dynamics,
carbon dynamics and
water/energy exchange
in high latitudes
Percent Area Burned
Percent Area Burned in IGBP Transects
Alaska
BFTCS
Finland
EST
FEST
1.0
0.5
0.0
al
al
e
e
or
or
b
b
a
n
r
r
t
he
ex
t
u
o
s
a
re
l
bo
-tu
t
s
e
r
fo
a
a
r
d
n
tu
r
d
n
al
ne
i
p
a
tu
r
d
n
Ground fires are typical in fire regime
of Scots Pine Forests in Central Siberia
Courtesy of Doug McRae
Crown fires are typical in fire regime of Boreal
Forests in Far East Siberia and North America
Courtesy of Doug McRae
Comparison of the average change in Seasonal Severity Rating (SSR) for Canada
and Russia using the Canadian General Circulation Model (GCM) under left) a 1 x
CO2, and right) a 2 x CO2 climate (from Stocks et al. 1998). Severity rating ranges
from extreme (red), high (orange), moderate (yellow) to low (green).
Regional Processes:
The Challenge of Multiple Disturbances
Joyce et al. Harvesting disturbances on U.S. forestland from
1600 to present. In preparation.
McGuire et al. Historical changes in carbon storage of the
eastern United States: Uncertainties associated with forest
harvest and agricultural activities. In preparation.
Overall Goals
• Develop land use model that allows native ecosystems
to convert to agriculture, harvest occurrence in
forests, and the creation the age cohorts following
harvest and cropland abandonment.
• Compare modeled age class distribution with
independent inventory data on stand age
distributions
• Use data sets on forest disturbance to drive the
Terrestrial Ecosystem Model (TEM) and evaluate how
assumptions about CO2 fertilization and depletion
of soil N by agricultural activities influence estimates
of changes in carbon storage of the eastern US
Methods to Estimate Harvest Area
• Anecdotal information prior to 1952
• Used inventory data summarized by state/region
from 1952, 1962, 1977, 1987, 1992, 1997, and 2002
• 1600 to 1952
– Trend extrapolation based on state population
– Assume no harvest disturbance prior to
European settlement
• 1952 to 2002
– Model harvested area using inventory data
(volume, removals, timberland and forest area)
and the limited data available on actual
harvested area
– Linear interpolation between inventory years
Development of the Land Use Model
• Agricultural Land Use
– If cropland increases, conversion
draws from oldest native vegetation,
with a preference for secondary growth.
– If cropland decreases, the oldest
cropland is converted back to native
vegetation
• Forest Harvest
– Harvest oldest native vegetation first,
with a preference for primary forest
Modeled estimates of total forestland area
follow the temporal dynamics of inventory
forestland estimates and are within 6 to 10%.
USA Forest Area Comparison
1200
Acres (millions)
1100
1000
900
800
700
Model Estimate
600
1600
1649
1698
1747
1796
Year
Inventory Estimate
1845
1894
1943
1992
Forest Harvest Area by Region and US
1980-90 FIA Data and Modeled Estimates
12,000
FIA 1980-90 Estimates
Adjusted Ratio Estimates 1992
Annual Acres Harvested (thousands)
10,000
8,000
6,000
4,000
2,000
0
Alaska
Pacific NW
Pacific SW
Intermountain
Great Plains
North Central
Northeast
South Central
Southeast
United States
Summary: Estimating Harvested Area
• Development of a method to obtain nationally
consistent estimates of harvested area from 1600
to 2002
• Linked forest land use change with agricultural
land use; resulting projections of forest land are
within 6 to 10 percent of recent inventory
• Comparison with independent data on stand age
is good where harvest is the major disturbance
• Where other disturbances such as fire,
comparison of stand-age distributions are weak
NET
CO2
Concentration
Climate
(Temperature,
Precipitation)
Landuse
Map
NPP
RH
Conversion
Flux
Fire
Disturbance
TEM
Carbon
Pools
Product
Decay
Flux
1 yr
10 yr
100 yr
Product Pools
Simulating the Effects of CO2, Climate, Forest
Harvest, and Cropland Establishment and
Abandonment by TEM
Comparison of forest growth curves
between TEM and Birdsey (1995)
Southeast Region Coniferous Forest
18000
TEM vegc
TEM ± 2 stdev
Southern Pine Plantation, site index 79+
Natural Pine, site index 79+
Natural Pine, site index 60-78
16000
14000
g C m-2
12000
10000
8000
6000
4000
2000
0
0
10
20
30
Stand Age
40
50
Effects of Cropland Establishment and Abandonment
on Soil Carbon and Nitrogen Storage
a) Soil Organic Carbon
14000
12000
g C m-2
10000
8000
6000
4000
2000
0
1860
1880
1900
1920
1940
1960
1980
2000
b) Soil Organic Nitrogen
400
350
g N m-2
300
250
200
150
100
50
1860
1880
1900
1920
1940
Year
Cultivated
1960
1980
2000
Northeast Region
Temperate Deciduous, VegC
Temperate Coniferous, VegC
18000
18000
maximum soil N loss
15000
after ag
never harvested
-2
12000
gCm
gCm
-2
15000
maximum soil N loss
9000
12000
9000
6000
6000
3000
3000
0
0
0
20
40
60
80
100
120
0
18000
40
60
80
100
120
minimum soil N loss
15000
12000
12000
-2
15000
gCm
-2
minimum soil N loss
gCm
20
18000
9000
9000
6000
6000
3000
3000
0
after ag
never harvested
0
0
20
40
60
80
Stand Age
100
120
0
20
40
60
80
100
120
Stand Age
Forest growth as a function of stand age in the TEM simulations is sensitive to assumptions about
the effects of agriculture on the depletion of ecosystem nitrogen stocks through time. When
nitrogen lost in agricultural production is not replaced (maximum N loss), forest regrowth after
agricultural abandonment is not able to achieve the biomass of forests that were never harvested.
When the lost nitrogen is replaced immediately after lost (minimum N loss), forest regrowth after
agricultural abandonment is able to achieve the biomass of forests that were never harvested.
Change in Vegetation Carbon Stocks in the Northeast
1000
min N loss, transient CO2
min N loss, constant CO2
max N loss, transient CO2
max N loss, constant CO2
800
Tg C
600
400
200
0
-200
1950
1960
1970
1980
1990
2000
Average annual vegetation C flux 1988-1992 (Tg C)
maximum
N loss$
Birdsey
and Heath*
minimun N
loss$
Northeast
22.1
21.7
33.5
Southeast
-4.8
8.2
16.5
Northeast
16.2
21.7
23.6
Southeast
-7.3
8.2
6.2
transient CO2$
constant CO2$
$ TEM
simulations (forest cells only)
* Birdsey and Heath posted on the web the carbon estimates in forest
land for 1987, 1992, and 1997 by state at
http://www.fs.fed.us/ne/global/pubs/books/epa/index.html
Change in Soil Carbon Stocks in the Northeast
100
50
0
Tg C
-50
-100
-150
min N loss, transient CO2
min N loss, constant CO2
max N loss, transient CO2
max N loss, constant CO2
-200
-250
-300
1950
1960
1970
1980
1990
2000
Conclusions
• Biospheric process models provide a mechanistic means of
evaluating the relative role of different drivers of changes in
regional carbon storage, but are poorly constrained by extant
atmospheric data.
• At the regional scale, changes in carbon storage may be affected by
responses to drivers that affect ecosystem physiology (e.g.,
CO2, climate, O3, N deposition) as well as changes that affect
ecosystem structure (e.g., disturbance and land use).
• It is important to account for historical legacies associated with
disturbance regimes like fire.
• Age class distributions are generally the outcome of multiple
disturbances, and it is a challenge to identify all of the
disturbances that need to be considered.
• Comparison with inventory analyses is useful, but may not resolve
controversies about the relative role of different drivers of
changes in regional carbon storage.