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G.C. Hurtt, S. Frolking, M.G. Fearon, B. Moore IIIE. Shevliakova, S. Malyshev, S.W. Pacala, R.A. Houghton
The Underpinnings of Land-Use History Three Centuries of Global Gridded Land-use TransitionsWood Harvest Activity, and Resulting Secondary Lands
PrincetonUniversity
Woods HoleResearch Ctr.
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The Global Scale of Human Activities
• The concentrations of several greenhouse gases have substantially increased in the atmosphere.1
• Anthropogenic N fixation now exceeds natural N fixation.2
• More than 50% of available freshwater is appropriated for human purposes.3
• Approx. 65% of marine fish stocks are fully exploited, or over exploited.4
• We are now in the 6th great extinction event.5
(1) IPCC 2001 (2) Kaiser 2001 (3) Postel et al 1996 (4) FAO 2000 (5) Lawton and May 1995; Pimm et al 1995. See also Steffen et al. 2003.
Land-use• Nearly 50% of the land surface has been transformed
by direct human action.1
• > 25% of forests have been cleared.2
• Habitat destruction is the primary risk for species extinctions.3
• Land-cover change affects regional and global climate.4
• Land-use change is an important and highly uncertain term in the global carbon budget.5
• Net re-growth on recovering “secondary” lands is the dominant carbon sink mechanism in some regions.6
(1) Vitousek et al 1986; Turner eet al 1990; Daily 1995 (2) Waring & Running 1998. (3) UNEP 2002; Sala et al 2000; (4) Pielke et al. 2002; Roy et al 2004 (5) IPCC 2001. (6) Caspersen et al., 2000; Pacala et al 2001; Hurtt et al, 2002. See also Steffen et al 2003.
Understanding the Consequences of Land-use Activities
• Patterns of land-use • Biogeochemistry on managed lands• Management practices • Fate of agricultural products• Land-use transitions • Earth System interactions
Key Questions
• What are the patterns of the land-use transition events that produced the patterns of agriculture and logged forests?
• What are the spatial patterns and age of lands recovering from prior land-use activities?
• What is the net effect of land-use change events that release carbon, and the carbon sinks provided by recovering “secondary” lands?
The Mathematical Structure of aLand-use History Reconstruction
l1
l2
l3
…
a11 a12 a13 …
a21 a22 a23 …
a31 a32 a33 …
… …
l(x,y,t+1) = A(x,y,t) l(x,y,t)
t+1 t
longitude
latit
ude
time
l1
l2
l3
…
Global, 1deg, 300 y, 4D: ~93x106 unknowns!
gridded (1°x1°) land-use states
1700-2000
gridded (1°x1°) potential biomass density
and recovery rate
national annual wood harvest
1700-2000
gridded (1°x1°) land-use transitions 1700-2000
INPUT OUTPUTMODEL
• residency time of agriculture
• inclusiveness of wood harvest statistics
• prioritization of land for conversion/logging
• spatial pattern of wood harvesting within countries
gridded (1°x1°) secondary land areaand age 1700-2000
Klein Goldewijk, 2001
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a)
c) d)
b)
Region secondary forest area
FAO ( 1998)a Rangeb
N. & C. America 4.6 0.6 Ğ 3.7
S. America 3.2 0.1 Ğ 2.3
Africa 2.5 0.2 Ğ 1.6
Eurasia 4.2 0.8 Ğ 14.0
Oceania 0.5 0.0 Ğ 0.3
Global 15.0 2.1 Ğ 21.9
1 a FAO (1988) total values do not include all countries, but are estimated to be within <10% of FAO total global forest area.b Ranges from data-based runs.
Additional Results• Estimates of wood harvest including slash (1850-1990)
– This Study: 100 Pg– Houghton (1999): 106 Pg
• Estimates of wood clearing for agriculture (1850-1990)– This study: 105-158 Pg– Houghton (1999): 149 Pg
• Area of forest land in shifting-cultivation fallow (2000)– This study: 4.56-6.19 x 106 km2
– FAO: 4.42 x 106 km2
• Rates of clearing land in shifting cultivation– This study: 0.48-0.65 x 106 km2 y-1
– Rojstaczer et al. (2001): 0.6-0.09 x 106 km2 y-1
• U.S. Forests – This study: Secondary 94-99% – This study: Mean age of Eastern forests 33-42y – FIA based estimate: Mean age of Eastern forests 38y
Key Findings• 42-68% of land surface was impacted by human
land-use activities (agriculture + wood harvest) 1700-2000.
• Total secondary land area increased 10-44 x 106 km2 during this period; about half is forested.
• Wood harvesting and shifting cultivation generated 70-90% of secondary land; permanent agriculture changes generated the rest.
Differences Between Reconstructions
U.S. Forest Inventory Plots
http://www.fia.fs.fed.us/
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0
40
Hei
ght (
m)
0 100Intensity
Cumulative Intensity0 1.0
25 m
8 km
1 km
Lidar Remote Sensing of Vegetation Height
http://icesat.gsfc.nasa.gov/intro.html
Multi-angle Imaging SpectroRadiometer (MISR)
http://www-misr.jpl.nasa.gov
Global C Budget (PgC/y)
1980s 1990sAtm. Increase 3.3+/-0.1 3.2+/-0.1
Emissions 5.4+/-0.3 6.3+/-0.4
Ocean-Atm. Flux -1.9+/-0.6 -1.7+/-0.5
Land-Atm. Flux* -0.2+/-0.7 -1.4+/-0.7
Land Use 1.7(0.6-2.5) NA
Residual Terrestrial Sink
-1.9(-3.8-0.3) NA
IPCC, 2001
Hurtt et al, 2002
U.S. Net Carbon Flux From Land-use Changes
Biomass kg C/m2 Undisturbed Fraction
1900
1800
2000
0 26 0 1
Shevliakova et al, Submitted
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Summary/Conclusion• This study provides the first global gridded estimates of land-use
transitions (land conversions), wood harvesting, and resulting secondary lands annually, for the period 1700-2000
• Major results are consistent with large sets of input data, and compare favorably to aggregated independent estimates.
• To best refine these estimates, new efforts are needed to characterize vegetation structure globally using remote sensing and field data.
• Additional future challenges include: understanding the dynamics on agriculture lands (including management), creating integrated models capable of tracking land-use activities and estimating their consequences, and developing consistent models of land-use in the future.