Land use change and terrestrial carbon cycle

Xiaojuan YangApril 17,2003

Outline

• Significance of land use change to terrestrial carbon cycle

• Data

• Approach

• Results and conclusions

1.6 ± 0.8 6.3 ± 0.6 3.2 ± 0.2 1.7 ± 0.5 3 ± ???

The role of terrestrial ecosystem in the global carbon budget is uncertain

The net flux of carbon between terrestrial ecosystem and the atmosphere results from two independent processes:

Direct human activity(deliberate)

Natural causes(inadvertent)

Changes in land use, harvest of wood…..

Elevated CO2, nitrogen deposition,climate change…

Purpose

Present an estimate of annual changes in terrestrial carbon storage andemission 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

• 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

Biomass type Carbon in vegetation

(10**6g/ha)

Tropical moist forest 200-250

Tropical dry forest 140-150

Temperate forest 135-160

Boreal 90

Woodland 27-55

grassland 7-10

Desert scrub 3-6

The amount of carbon per hectare in the live vegetation of different ecosystem

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 betweenthe 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.

ReferencesHoughton, 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.