The Net Carbon Flux from Deforestation and Re-growth in the
Brazilian Legal Amazon: Comparison of Bookkeeping and
Process Based Approaches
Adam I. Hirsch1, Richard A. Houghton1, William S. Little2
1The
Woods Hole Research Center, P.O. Box 296, Woods Hole, MA. 02543, USA
2The Woods Hole Oceanographic Institute, Woods Hole, MA., USA
Presented at the
International LBA
Scientific Conference
2nd
Contact: Adam at [email protected]
Bookkeeping vs. Process-Based Approaches
•
1.
2.
3.
Bookkeeping model (Houghton et al., 2000)
Fixed forest productivity – proportional to mature forest biomass
Doesn’t consider litter and soil carbon
Mature forest biomass is taken from maps generated from measurements
•
1.
2.
3.
3.
Process-Based Model
Productivity is a function of climate, soil qualities, and calculated Leaf Area Index
Includes full water balance using Penman-Monteith evapotranspiration
Carbon passes from the atmosphere, through detritus and soil carbon, and back
into the atmosphere
Mature forest biomass is generated internally by the model
•
Both use the same deforestation rates, but different land use dynamics
The Net Flux Calculation
F(t) = Net Carbon Flux in year t (1970-1998)
fi = Fraction of deforested area in climate class i
F(t)= fi *Ci a(t- ) *r( )
Ci = Total ecosystem carbon storage in climate class i
i=1
τ =1
a(t-τ) = Annual Deforestation rate, ha/yr
r(τ) = Flux response curve, normalized by steady state Ci
Average biomass
Adding contribution
of deforested area from all years to present
100
∑(
29
)∑
τ
τ
The CARLUC Carbon Cycle Model: a process-based carbon cycle model used to determine Ci and the net
C flux due to disturbance and recovery, which are part of r(τ)
Dynamic Land Use Change Model: Used to determine timing of land use transitions, which is part of r(τ)
The CARLUC Carbon Cycle Model
Atmosphere
Wood
Products
Charcoal
NPP
Stems Leaves
Coarse Woody
Debris
Roots
Detritus
Humus
NPP = 0.012*0.45*α*f(SW)*f(T)*f(VPD)*PAR*(1-e-0.7*LAI)
“Climate class” = index for scaling model results to the Basin level
• NPP and water balance based on 3-PG (Landsberg & Waring, 1997)
• α = optimal quantum efficiency
• 0.45 = discounting factor for plant respiration
• f(X) = multipliers representing water, temperature, and humidity limitations, viz. 3-PG
• Allocation and live carbon turnover similar to CASA (Potter et al., 1997)
• Climate inputs from East Anglia CRU 1961-1990 0.5o monthly averages
• Radiation input from Dr. Rachel Pinker, 1990-1992 0.5o monthly averaged PAR
• Soil Texture from Dr. Chris Potter (8 km)
• Maximum PAW from Paul Lefebve at WHRC
• Aggregating the Amazon into “climate classes” allows substantial savings over simulating every 64 km2 pixel.
• During deforestation, 20% of biomass is combusted, 8% harvested for wood products, 2% is converted to
charcoal, and 70% left to decompose, as in Houghton et al. (2000).
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BETA
CARLUC Sensitivity Testing
0.3
0.2
0.1
0
-0.3
-0.4
Parameter
β = (total C+10% – total carbon-10%)/total Cdefault
Ecosystem Carbon Partitioning – Rio Branco
Mature Forest
DPM
1%
RPM
12%
HUM
14%
CWD
4%
Live Wood
65%
Fine Root
2%
Live Leaf
2%
DPM = Decomposable Plant Material
HUM = Humus
RPM = Resistant Plant Material
CWD = Coarse Woody Debris
IOM = Inert Organic Matter ~ 1.5*(DPM + RPM + HUM)
Soil Carbon Model
• Based on the Roth-C model (Jenkinson, 1990)
• Calibrated to match Trumbore et al. (1995) C and bulk ∆14C
measured to 8 m depth near Paragominas in 1992
• Used to calculate fraction of decomposition passing to humus vs. CO2
Ci = Steady State Ecosystem Total Carbon Storage
Deforestation Pattern: fi
Fraction of 64 km2 Pixels Classified as
“Cleared” in TRFIC 1986 or 1992 Amazon Maps
100
∑ f *C
i
ι =1 i
= 145 tC/ha (slightly lower than Houghton et al., 2000)
Aboveground Live Biomass Comparison
22 field sites from Houghton et al. (2001) : 148±43 tC/ha
Model: 135±30 tC/ha
Biomass Recovery Dynamics
A G L B , tC /h a
100
CARLUC BASELINE
80
HOUGHTON et al. (2000)
60
Salimon & Brown (2000)
40
Uhl et al. (1988) light
20
Uhl et al. (1988) moderate
0
0
5
10
15
20
25
Years
• Houghton et al. (2000) assumed 75% recovery of biomass in 25 yr
• CARLUC predicts much slower growth, coincidentally falling equally
close to observations from the dominant land use pattern in Eastern
Amazonia (Uhl, Buschbacher & Serrão, 1988).
• We have not yet included the initial high-productivity pioneer phase in the model
Dynamic Land Use Change Model
FAO
Skole & Tucker, 1993
1
2
INPE
4
3
1 = Primary Forest Clearing: a(t-τ) 3 = Houghton et al. (2000) Abandonment
2 = Simulated Abandonment
4 = Simulated Re-clearing
Primary
Forest
Agricultural
Land
Re-growing
Forest
Calibrated with 1986, 1992, 1996 TRFIC Land Cover Classification Maps
Comparison with Satellite-Derived Information
Cleared Forest Area
A = Houghton et al. (2000)
B = Land Use Model
C = TRFIC maps
Secondary Forest Area
A = Houghton et al. (2000)
B = Land Use Model
C = TRFIC maps (too low)
• Houghton et al. (2000): annual abandonment = 30% of annual deforestation, no
re-clearing of secondary forest
• Present model: approx. 7 years in agriculture followed by 7 years as re-growing
before being re-cleared
• TRFIC maps may underestimate secondary forest area (viz. Alves & Skole, 1996)
r(τ) = Normalized Flux Response Curve – Combination of the 2 Models
3 Cycles of Cut and Burn, then 7 Years Fallow
Flux Normalized by Steady State Carbon Storage
Net Carbon Flux Results 1970-1998
Cumulative Net Release ~ 4.5 GtC
Uncertainty (1 SD ~ 35%) estimated using Monte-Carlo technique for mature forest
biomass and flux response
Summary and Conclusions
• Results are very similar to Houghton et al. (2000)
• In present study, slower biomass recovery offset
by greater area of re-growing forest predicted by
land use model and slightly lower AGLB
• Land use model would benefit from accurately coregistered multi-temporal Basin-wide land cover
maps, allowing pixel by pixel change detection
• Ecological model would benefit from more realistic
treatment of secondary succession
• We intend to use the model to study the carbon
budget impact of Basin-wide logging and
accidental fire