Tropical Mexico's recent land-use change: A region's contribution to the global carbon cycle

We applied modeled biomass density estimates to changes in land use/land co ver (LU/LC) statistics for the intensively impacted and highly fragmented l andscape of tropical Mexico to estimate the flux of carbon (C) between terr estrial ecosystems and the atmosphere between 1977 and 1992. Biomass densit ies were assigned to hybrid LU/LC classes on vegetation maps produced by Me xican governmental organizations and, by differencing areas and biomass C p ools, net C flux was calculated in the eight-state tropical region of south east Mexico. These states, representing tropical Mexico, experienced a mean annual deforestation rate of nearly 559 000 ha/yr, or 1.9%, between 1977 a nd 1992. The total area of closed forests decreased by 26%, open/fragmented forests decreased by 31%, and agroecosystem areas increased by 64%. Total mean biomass densities ranged from a high of 265 Mg/ha in the Veracruz stat e tall/medium tropical evergreen forest class to a low of 12 Mg/ha in the c ultivated land class (several states). We estimate that a total of 280 Tg C were released from the terrestrial biosphere during the 15-yr period cover ed by our study, equal to nearly 20% of the region's 1977 biomass C pool. T he study region, while comprising just 24% of Mexico's surface area, contri buted 36% of the net national C emissions from LU/LC change.