Woody debris stocks and fluxes during succession in a dry tropical forest

Abstract

In Southern Mexico, shifting cultivation is creating a mosaic of agricultural lands, secondary forests, and disturbed mature forests (montañas). Increased land-use change, due to population and market pressures has changed the structure and function of these forests. This study investigates the stocks and fluxes of woody debris during the course of secondary succession. We inventoried fine (≥1.8 cm to ≤10 cm diameter) and coarse woody debris (≥10 cm diameter) stocks in 28 stands. In a subset of montañas and secondary forest fallows, we monitored inputs and decomposition over a 2-year period. Total woody debris stocks were largest in montañas (37.46 Mg/ha) and in the first year after clearing (milpa, 51.62 Mg/ha). Woody debris was 22% of the total aboveground biomass in montañas and 88% in milpas. Although stocks were highly variable in secondary forest, coarse woody debris stocks were roughly three times larger than fine woody debris stocks. Coarse woody debris stocks decreased following cultivation for 10–15 years, until inputs exceeded losses to decomposition. Inputs were higher in montaña (0.91 Mg ha −1 year −1) than in secondary forest (0.11 Mg ha −1 year −1). Coarse woody debris inputs were higher during the dry season, while fine woody debris inputs tended to be higher during the wet season. Decomposition varied significantly among tree species, with decomposition rate constants from 0.124 to 0.643 year −1 for coarse woody debris and 0.368–0.857 year −1 for fine woody debris. In young forests, when woody debris stocks are largest, cultivation history is the most important factor in predicting stocks of woody debris. As forest age increases woody debris processes, both inputs and decomposition, become increasingly important factors in regulating woody debris stocks, and therefore age is a better predictor of woody debris stocks in older forests.