Regional scale variation in forest structure and biomass in the Yucatan Peninsula, Mexico: Effects of forest disturbance

Abstract

Aboveground biomass is a key variable in understanding the role of tropical forests in the global carbon cycle. The forests of the Yucatan Peninsula form part of the largest remaining tract of Mesoamerican forests, where the predominant land use is still slash-and-burn agriculture. Previous estimates of aboveground live phytomass of late-successional forests in this region vary almost twofold, but are derived from relatively few forest plots. We estimate aboveground forest biomass using data from 243 inventoried forest plots (totalling 58.5 ha), ranging across a disturbance gradient from nearly intact to severely degraded forests. We assess the effects of environmental and disturbance variables on forest basal area, stand-level wood specific gravity and aboveground biomass. Major differences in basal area and aboveground biomass were explained by levels of human disturbance (clear-cutting, logging, and fire disturbance), whereas edaphic factors played only a minor role. Total mean phytomass density estimates ranged from 28.8 ± 3.8 mg ha −1 in plots aged 10–15 years to 191.9 ± 9.5 mg ha −1 in undisturbed old-growth forest plots (>50 years). Severe logging and fire disturbance reduced AGB in late-successional plots (30–50 years) by 36% and 37%, respectively. Stand-level wood specific gravity increased with succession, due to an increase in the proportion of total basal area contributed by high wood density genera. Logging intensity had a small additional effect on stand-level wood specific gravity. Incorporating stand-level wood specific gravity into the algorithm explained only an additional 4% of the variation in estimates of aboveground biomass, which was largely determined by basal area. However, ignoring plot-level variation in wood specific gravity resulted in overestimates of 19% in plots aged 10–15 years. Our aboveground biomass estimates were highly comparable with previous studies using the same allometric equations, and fell within the highest range of estimates reported for tropical dry forests. Forest of this region still retains a significant carbon stock, but rates of biomass recovery (2.8 ± 0.2S.E. mg ha −1 year −1) were low compared to other neotropical forests.