Effects of Land Cover
the Carbon Cycle in Southern China
Rapid industrialization in China will lead to the
change in type of land cover. Dr. Dye will explain the land cover
change in a rapidly developing region of China and its effect.
Dennis Dye ( Group Leader, Ecosystem Change
Research Program, FRSGC )
Rising human population, particularly when coupled
with rapid industrial and economic development, is a major cause
of global environmental change. One of the most visible types of
change caused by human activities is land cover change: the conversion
of land cover from one cover type (such as forest or grassland)
to another type (such as agriculture or urban). Land cover change
typically involves altering or removing the vegetation in the landscape.
Such disturbances to the landscape reduce the capacity of a region's
ecosystems to contribute to important biospheric processes, including
the terrestrial carbon cycle. The most common types of land cover
change cause a net loss of vegetation from the landscape and disturb
the underlying soil. This can result in a net release of carbon
stored in vegetation and soils to the atmosphere, where it contributes
to rising atmospheric CO2 concentrations,
and potentially, global warming.
An improved understanding of the terrestrial
carbon cycle and its role in global climate change requires information
on the patterns and rates of land cover change and their effects
on ecosystem functioning. Satellite remote sensing and ecosystem
modeling work in the Ecosystem Change Research Program of Frontier
Research System for Global Change (FRSGC) are designed to help achieve
this understanding. Some of this research has focused on land cover
change in a rapidly developing region in the southern part of the
People's Republic of China (PRC) (Fig. 1).
||Location of the Pearl River Delta (PRD) region in the
People's Republic of China. The study area corresponds to a single
Landsat Thematic Mapper scene.
Satellite-based studies indicate that land cover change
in the PRC is occurring at unprecedented rates. A recent remote sensing
analysis by Seto (2000) showed that between 1988 and 1996, urban land
areas in the greater Pearl River Delta region in the southern PRC increased
by over 300%, while natural and agricultural land declined by approximately
6% and 10%, respectively (Fig. 2). How have these changes affected the
terrestrial carbon cycle in the region? To answer this question, we employed
satellite remote sensing, ecosystem process modeling, and ecological data
to investigate the effects of the land cover change on two components
of the carbon cycle: net primary production (NPP) and ecosystem carbon
storage (Dye et al., 2002).
||Major land cover classes in the Pearl River Delta
region. Locations of land cover change during 1988 to 1996 are
depicted in yellow color. These changes have resulted in a net
release of carbon to the atmosphere.
These images depict the city of Shenzhen in the Pearl
River Delta as observed by the Landsat TMsatellite sensor in 1988
(top) and 1996 (bottom).
Green vegetation is indicated
by red color and urban areas are indicated by yellow color. Rapid
urbanization associated with economic development has removed vegetation
from the landscape, causing a net loss of carbon stored in the region's
The results from our analysis suggest that land
cover change in the Pearl River Delta region between 1988 and 1996 affected
the regional carbon cycle by reducing both the annual rate of NPP and
the size of the terrestrial carbon pool. The dominant mode of land use
change was the conversion of natural and agricultural land to urban uses.
Urbanization generally involves the removal of vegetation (forests, grassland,
or agricultural crops) and replacing it with roads, buildings, and other
urban infrastructure. As a consequence of the urbanization, the annual
amount of atmospheric carbon assimilated into vegetation through NPP declined
by approximately 1.5 Megatons (-7.5%). This result indicates a reduction
in the total photosynthetic capacity and carbon sequestration potential
of the region's ecosystems. More than half (55%) of this reduction in
NPP is attributable to the loss of agricultural land. The urbanization
released about 12 Megatons carbon from the terrestrial carbon storage
pool, of which 19% was from soils and 81% from vegetation. This amount
of carbon released is about 13% the estimated annual amount of carbon
released by fossil fuel combustion in the Pearl River Delta region. Because
urbanization is the dominant type of change, there is low potential for
the ecosystems to recapture the lost carbon through vegetation regrowth.
Thus, land cover change is responsible for a sustained reduction in the
size of the terrestrial carbon pool in the Pearl River Delta region.
The future course of the socioeconomic driving forces
that influence land cover change in the PRC, in combination with potential
climate change, will determine whether these effects on the region's carbon
cycle become exacerbated or diminished in the coming decades.
||K., 2000, Monitoring andmodeling land-use changein the Pearl River
Delta,China, using satellite imageryand socioeconomic data,Ph. D.
thesis, Department of Geography, Boston University.
||D., Hinchliffe, T., andWoodcock, C., 2002, Effects ofland use change
on the carboncycle in southern China. (Submitted to Asian Journalof