Tropical forests and atmospheric carbon dioxide

doi:10.1016/S0169-5347(00)01906-6

Trends in Ecology & Evolution

Volume 15, Issue 8, 1 August 2000, Pages 332-337

https://doi.org/10.1016/S0169-5347(00)01906-6 Get rights and content

Abstract

Tropical forests play a major role in determining the current atmospheric concentration of CO₂, as both sources of CO₂ following deforestation and sinks of CO₂ probably resulting from CO₂ stimulation of forest photosynthesis. Recently, researchers have tried to quantify this role. The results suggest that both the carbon sources and sinks in tropical forests are significantly greater than previously thought.

Section snippets

A case study of the tropical forest carbon cycle

The C dynamics of a forest are dominated by the assimilation of CO₂ through gross photosynthesis (G_p); the release of C through autotrophic (plant) respiration, R_a; the transfer of C to the soil in the form of leaf, wood and root litter, and the exudation of organic compounds into the rhizophere⁶; and the eventual release of this soil C back to the atmosphere through decomposition and respiration by microbes and other heterotrophs (R_h). There are few tropical sites where the internal forest C

Carbon emissions from tropical deforestation: E_trop

The three principal zones of tropical forest are in South America, central Africa and southeast Asia. All three areas are undergoing rapid deforestation, primarily because of clearing for croplands (55%) or cattle pasture (20%), or because of the expansion of logging and shifting cultivation (12% each)¹⁸. Table 1 shows the extent of tropical forests in 1990 (Ref. 3), and the rates of clearance between 1980–1990 and 1990–1995 (Ref. 19). The Americas account for over 50% of tropical forest area,

CO₂ in the tropical atmosphere

An independent view on terrestrial C emissions can be obtained by examining the temporal and spatial variation of CO₂ concentrations in the atmosphere. Recent studies have attempted to provide continental-scale maps of the distribution of C sinks and sources26, 27, 28. There are small gradients in mean atmospheric CO₂ concentration between hemispheres and between continents, caused primarily by the uneven spatial distribution of surface C sources and sinks, and by relatively slow mixing by the

A tropical carbon sink: Δ_trop

The net C budget of an area of forest is the balance between net production and heterotrophic respiration. As shown in Fig. 1b, these two terms must be in approximate balance because any change in N_p eventually produces a corresponding change in R_h, with a lag time equal to the sum of the soil and the biomass residence times. For example, if there is a short-term increase in R_h, because of an increase in soil temperature, the soil C stocks will eventually decrease to bring R_h back to a level

A revised global carbon budget?

In this perspective, we have examined recent developments in the study of the productivity and C balance of tropical forests, with any eye to converging on a consistent picture of the tropical forest C sink. Such a consistent picture has not yet emerged, but there have been several major new developments. Our main conclusions are listed in Box 1.

It seems probable that tropical forests are greater sources and sinks of C than previously estimated. We can suggest tentative revisions to the global

Future directions

The research areas reviewed here can all be expected to make significant progress over the next decade. There will be a substantial expansion of data sets in all fields, but methodological issues must still remain a focus of research.

For studies based on global atmospheric CO₂ concentrations, there needs to be an expansion of data points in poorly monitored regions, including tropical oceanic and continental re-gions, and improvements in the modelling of global trace gas transport,

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Trends in Ecology & Evolution

PerspectivesTropical forests and atmospheric carbon dioxide

Abstract

Section snippets

A case study of the tropical forest carbon cycle

Carbon emissions from tropical deforestation: Etrop

CO2 in the tropical atmosphere

A tropical carbon sink: Δtrop

A revised global carbon budget?

Future directions

Appl. Soil Ecol.

Climate Change 1995: The Science of Climate Change

Forest Resources Assessment 1990 – Tropical Countries

FAO Forestry Paper

Primary production of the biosphereintegrating terrestrial and oceanic components

Science

Terrestrial ecosystems and the global carbon cycle

Glob. Change Biol.

Carbon dioxide transfer over a central Amazonian rain forest

J. Geophys. Res.

Strategies for measuring and modelling carbon dioxide and water vapour fluxes over terrestrial ecosystems

Glob. Change Biol.

Atmospheric–biosphere exchange of CO2 and O3 in the central Amazon forest

J. Geophys. Res.

Carbon dioxide uptake by an undisturbed rain forest in South-West Amazonia 1992–1993

Science

Combustion completeness in a rainforest clearing experiment in Manaus, Brazil

J. Geophys. Res.

Greenhouse gases from deforestation in Brazilian Amazonianet committed emissions

Clim. Chang.

Soil carbon pools and world life zones

Nature

The carbon balance of tropical, temperate and boreal forests

Plant Cell Environ.

Gross and net primary production and growth parameters

Productivity of tropical forests and tropical woodlands

Carbon fluxes and productivity of tropical forests

The annual net flux of carbon to the atmosphere from changes in land use 1850–1990

Tellus

State of the World’s Forests 1997

Global warming and tropical land-use change: greenhouse gas emissions from biomass burning, decomposition and soils in forest conversion, shifting cultivation and secondary vegetation

Clim. Chang.

Emissions of carbon from forestry and land-use change in tropical Asia

Glob. Change Biol.

Large-scale impoverishment of Amazonian forests by logging and fire

Nature

Ground fires as agents of mortality in a Central Amazonian forest

J. Trop. Ecol.

Tropical deforestation and habitat fragmentation in the Amazonsatellite data from 1978 to 1988

Science

Perspectives
Tropical forests and atmospheric carbon dioxide

Carbon emissions from tropical deforestation: E_trop

CO₂ in the tropical atmosphere

A tropical carbon sink: Δ_trop

Atmospheric–biosphere exchange of CO₂ and O₃ in the central Amazon forest