Transcript The Underpinnings of Land Use History

The Underpinnings of Land-Use History
Three Centuries of Global Gridded Land-use Transitions
Wood Harvest Activity, and Resulting Secondary Lands
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G.C. Hurtt, S. Frolking, M.G. Fearon, B. Moore III
E. Shevliakova, S. Malyshev, S.W. Pacala, R.A. Houghton
Princeton Woods Hole
University 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 19 9 6 (4) FAO 2000 (5) Lawton and May 19 9 5; Pimm et al
19 9 5. 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 1
9 86; Turner eet al 19 9 0; Daily 19 9 5 (2) Waring & Running 19 9 8. (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
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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
latitude
l(x,y,t+1) = A(x,y,t) l(x,y,t)
l1
a11 a12 a13
l2
a21 a22 a23
…
l2
l3
a31 a32 a33
…
l3
…
…
…
…
…
l1
t+1
longitude
Global, 1deg, 300 y, 4D:
~93x106 unknowns!
t
INPUT
gridded
(1°x1°) landuse states 17002000
gridded (1°x1°)
potential biomass density
and recovery rate
national annual
wood harvest
1700-2000
MODEL
• residency time of agriculture
• inclusiveness of wood harvest
statistics
• prioritization of land for
conversion/logging
• spatial pattern of wood
harvesting within countries
OUTPUT
gridded (1°x1°)
land-use transitions
1700-2000
gridded (1°x1°)
secondary land area
and age 1700-2000
Klein Goldewijk, 2001
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a)
b)
c)
d)
Region
secondary forest area
FAO (1998)
Range
b
N. & C. America
4.6
0.6 Р 3.7
S. America
3.2
0.1 Р 2.3
Africa
2.5
0.2 Р 1.6
Eurasia
4.2
0.8 Р 14.0
Oceania
0.5
0.0 Р 0.3
15.0
2.1 Р 21.9
Global
1a
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) 17002000.
• 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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Lidar Remote Sensing of Vegetation Height
Cumulative Intensity
0
1.0
40
Height (m)
8 km
0
0
25 m
Intensity
100
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
1.7(0.6-2.5)
NA
-1.9(-3.8-0.3)
NA
Land Use
Residual
Terrestrial Sink
IPCC, 2001
U.S. Net Carbon Flux From Land-use Changes
Hurtt et al, 2002
Biomass kg C/m2
Undisturbed Fraction
1800
1900
2000
0
26
0
1
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.
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• To best refine these estimates,
new efforts are needed to
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are needed to see this picture.
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 landuse in the future.