TROPICAL FORESTS - THEIR PAST, PRESENT, AND POTENTIAL FUTURE-ROLE IN THE TERRESTRIAL CARBON BUDGET

In this paper we review results of research to summarize the state-of- knowledge of the past, present, and potential future roles of tropical forests in the global C cycle. In the pre-industrial period (ca. 1850 ), the flux from changes in tropical land use amounted to a small C so urce of about 0.06 Pg yr-1. By 1990, the C source had increased to 1.7 +/- 0.5 Pg yr-1. The C pools in forest vegetation and soils in 1990 w as estimated to be 159 Pg and 216 Pg, respectively. No concrete eviden ce is available for predicting how tropical forest ecosystems am likel y to respond to CO2 enrichment and/or climate change. However, C sourc es from continuing deforestation are likely to overwhelm any change in C fluxes unless land management efforts become more aggressive. Futur e changes in land use under a ''business as usual'' scenario could rel ease 41-77 Pg C over the next 60 yr. Carbon fluxes from losses in trop ical forests may be lessened by aggressively pursued agricultural and forestry measures. These measures could reduce the magnitude of the tr opical C source by 50 Pg by the year 2050. Policies to mitigate C loss es must be multiple and concurrent, including reform of forestry, land tenure, arid agricultural policies, forest protection, promotion of o n-farm forestry, and establishment of plantations on non-forested land s. Policies should support improved agricultural productivity, especia lly replacing non-traditional slash-and-burn agriculture with more sus tainable and approaches.