Transcript Land use change and terrestrial carbon cycle

Land use change and
terrestrial carbon cycle
Xiaojuan Yang
April 17,2003
Outline
• Significance of land use change to
terrestrial carbon cycle
• Data
• Approach
• Results and conclusions
The role of terrestrial ecosystem in the global carbon budget is uncertain
1.6 ± 0.8
6.3 ± 0.6
3.2 ± 0.2
1.7 ± 0.5
3 ± ???
The net flux of carbon between terrestrial ecosystem and
the atmosphere results from two independent processes:
Direct human activity(deliberate)
Changes in land use, harvest of wood…..
Natural causes(inadvertent)
Elevated CO2, nitrogen deposition,climate change…
Purpose
Present an estimate of annual changes in terrestrial carbon storage and
emission from land due to deliberate management of the land surface
Data
• Annual rates of land use change (expansion
and contraction of agriculture area and rates
of wood harvest)
• Carbon content of each ecosystem
Map of Nine geopolitical regions
Types of ecosystems
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Tropical moist forest
Tropical seasonal forest
Temperate evergreen forest
Temperate deciduous forest
Boreal forest
Tropical woodland and shrub land
Temperate woodland and shrub land
Tropical grassland
Temperate grassland
Tundra
Desert scrub
Swamp and marsh
Cultivated land
Pasture land
Data on carbon
The amount of carbon per hectare in the live vegetation
of different ecosystem
Biomass type
Carbon in vegetation
(10**6g/ha)
Tropical moist forest
Tropical dry forest
Temperate forest
Boreal
200-250
140-150
135-160
90
Woodland
grassland
27-55
7-10
Desert scrub
3-6
Approach
• Accounting for all of the carbon on an affected unit of land: live
vegetation, soil, woody debris, wood products. The fate of each of
the components was tracked in a bookkeeping model
• For each region, each type of ecosystem, and each type of land
use the area, carbon content, and flux of carbon were calculated
annually
Area of cropland (a) tropical regions
(b) temperate zone regions
Flows of carbon between
the major components of
terrestrial ecosystems and
the atmosphere as a result
of land use change over 140
year period 1850-1990
Conclusions
• Between 1850 and 1990, the area of cultivated lands, is estimated to
have increased by more than a factor of 4, from about 320*106ha in
1850 to 1360*106ha in 1990
• Total net flux of carbon from changes in land use is 124GtC over the
period from 1850 to 1990
• The annual net flux, globally, increased from 0.4GtC/yr in 1850 to
2.0GtC/yr in 1990
• The most important land use change was the expansion of agriculture
• Emissions from tropical Asia, Latin American accounted for almost all
of the global emissions.
References
Houghton, R. A. 1999. The annual net flux of carbon to the atmosphere from
changes in land use 1850-1990. Tellus 51B:298-313.
Houghton, R. A., and J. L. Hackler. 2001. Carbon flux to the Atmosphere from
land use changes:1850-1990. ORNL/CDIAC-131, NDP-050/R1. Carbon
Dioxide Information Analysis Center, U.S. Department of Energy, Oak Ridge
National Laboratory, Oak Ridge, Tennessee, U.S.A.
Houghton, R. A., R. D. Boone, J. R. Fruci, J. E. Hobbie, J. M. Melillo, C. A.
Palm, B. J. Peterson, G. R. Shaver, G. M. Woodwell, B. Moore, D. L. Skole,
and N. Myers. 1987. The flux of carbon from terrestrial ecosystems to the
atmosphere in 1980 due to changes in land use: Geographic distribution of the
global flux. Tellus 39B:122-139.