This document summarizes a study that reconstructed global patterns of land use change from 1700-2000 at a 1 degree resolution. The study estimated land conversions, wood harvesting, and resulting secondary lands annually. Key results found that 42-68% of the global land surface was impacted by human land use activities during this period. Total secondary lands increased by 10-44 million km^2, around half of which was forested. The study provides the first global gridded estimates of its kind, and results were generally consistent with other data sources. Remaining challenges include better understanding agriculture land dynamics and developing integrated models to estimate future land use change impacts.

1. 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.
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2. 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.

3. 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.

4. 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

5. 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?

6. The Mathematical Structure of a
Land-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
latitude
l1
l2
l3
…
Global, 1deg, 300 y, 4D:
~93x106 unknowns!

7. 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 area
and age 1700-2000

8. Klein Goldewijk, 2001

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13. a)
c) d)
b)

17. Reg ion s econ dary fore st area
FAO ( 1998)
a
Ran ge
b
N. & C . A mer ica 4.6 0.6 Ğ 3.7
S. A mer ica 3.2 0.1 Ğ 2.3
Afric a 2.5 0.2 Ğ 1.6
Eur asia 4.2 0.8 Ğ 14.0
Oc ean ia 0.5 0.0 Ğ 0.3
G lobal 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.

18. 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

19. 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.

21. Differences Between Reconstructions

22. U.S. Forest Inventory Plots
http://www.fia.fs.fed.us/

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24. 0
40
Height(m)
0 100
Intensity
Cumulative Intensity
0 1.0
25 m
8 km
Lidar Remote Sensing of Vegetation Height

25. http://icesat.gsfc.nasa.gov/intro.html

26. Multi-angle Imaging SpectroRadiometer (MISR)
http://www-misr.jpl.nasa.gov

27. 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

28. Hurtt et al, 2002
U.S. Net Carbon Flux From Land-use Changes

29. Biomass kg C/m2 Undisturbed Fraction
1900
1800
2000
0 26 0 1
Shevliakova et al, Submitted

30. QuickTime™ anda
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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.