Land-use change and carbon flux between 1970s and 1990s in central highlands of Chiapas, Mexico

We present results of a study in an intensively impacted and highly fragmen ted landscape in which we apply field-measured carbon (C) density values to land-use/land-cover (LU/LC) statistics to estimate the flux of C between t errestrial ecosystems and the atmosphere from the 1970s and 1990s. Carbon d ensities were assigned to common LU/LC classes on vegetation maps produced by Mexican governmental organizations and, by differencing areas and C pool s, net C flux was calculated from the central highlands of Chiapas, Mexico, during a 16-year period. The total area of closed forests was reduced by h alf while degraded and fragmented forests expanded 56% and cultivated land and pasture areas increased by 8% and 30%, respectively. Total mean C densi ties ranged from a high oi 504 tons C/ha in the oak and evergreen cloud for ests class to a low of 147 tons C/ha in the pasture class. The differences in total C densities among the various LU/LC classes were due to changes in biomass while soil organic matter C remained similar. We estimate that a t otal of 19.99 x 10(6) tons C were released to the atmosphere during the per iod of time covered by our study, equal to approximately 34% oi the 1975 ve getation C pool. The Chiapas highlands, while comprising just 0.3% of Mexic o's surface area, contributed 3% of the net national C emissions.