Recovery of biomass following shifting cultivation in dry tropical forests of the Yucatan

Land-use change in the tropics is creating secondary forest at an unprecedented rate. In the tropical Americas, mature dry tropical forest is rapidly being converted to secondary forest during the fallow period of shifting cultivation. This study addresses changes in forest biomass during forest recovery following shifting cultivation of maize (corn) in the Southern Yucatan Peninsular Region (SYPR), Mexico. We sampled stems >1 cm diameter at breast height at 36 study sites in three regions located along a precipitation gradient of 900-1400 mm/yr. Using allometric equations developed in the tropical Americas, we estimated total aboveground (TAG) biomass of trees, palms, and lianas. Biomass differed little between regions when, considering forests of a given age. Over the entire area, forest biomass increased rapidly during succession, from 20.9.Mg/ha in 2-5-yr-old forests to 136.4 Mg/ha in mature forests (logged in the past half century, but not cultivated). Within 12-25 yr, biomass reached half of mature forest levels, and we estimate recovery to pre-cultivation levels in 55-95 yr. Recovery to a pre-logged state may take 65-120 yr. In mature forests, the contribution of stems 1-4.9 cm dbh was consequential, comprising 15% of TAG biomass. Trends in both TAG biomass and basal area were driven by the contribution of trees, although in a few sites, the importance of palms and lianas to forest structure and biomass was considerable. Our results suggest that forest biomass in secondary dry tropical forests of the SYPR is profoundly influenced by forest age, and less,so by annual precipitation, while variability in forest structure depends more on differences in water availability and recent human disturbance.