Presentation on theme: "G.C. Hurtt, S. Frolking, M.G. Fearon, B. Moore III E. Shevliakova, S. Malyshev, S.W. Pacala, R.A. Houghton The Underpinnings of Land-Use History Three."— Presentation transcript:
G.C. Hurtt, S. Frolking, M.G. Fearon, B. Moore III E. Shevliakova, S. Malyshev, S.W. Pacala, R.A. Houghton The Underpinnings of Land-Use History Three Centuries of Global Gridded Land-use Transitions Wood Harvest Activity, and Resulting Secondary Lands Princeton University Woods Hole Research Ctr.
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 a Land-use History Reconstruction l1l2l3…l1l2l3… a 11 a 12 a 13 … a 21 a 22 a 23 … a 31 a 32 a 33 … … l (x,y,t+1) = A (x,y,t) l (x,y,t) t+1t longitude latitude time l1l2l3…l1l2l3… Global, 1deg, 300 y, 4D: ~93x10 6 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 INPUTOUTPUTMODEL 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 area and age 1700-2000
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 10 6 km 2 –FAO: 4.42 x 10 6 km 2 Rates of clearing land in shifting cultivation –This study: 0.48-0.65 x 10 6 km 2 y -1 –Rojstaczer et al. (2001): 0.6-0.09 x 10 6 km 2 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 10 6 km 2 during this period; about half is forested. Wood harvesting and shifting cultivation generated 70-90% of secondary land; permanent agriculture changes generated the rest.
Global C Budget (PgC/y) 1980s1990s Atm. Increase3.3+/-0.13.2+/-0.1 Emissions5.4+/-0.36.3+/-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 Use1.7(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/m 2 Undisturbed Fraction 1900 1800 2000 02601 Shevliakova et al, Submitted
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.