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 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

lati

tud

e

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 – 3.7

S. America 3.2 0.1 – 2.3

Africa 2.5 0.2 – 1.6

Eurasia 4.2 0.8 – 14.0

Oceania 0.5 0.0 – 0.3

Global 15.0 2.1 – 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

He

igh

t (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 1990s

Atm. 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.