Community dynamics during early secondary succession in Mexican tropical rain forests

Stand structure dynamics during early secondary forest succession were related to mortality, growth and recruitment rates, and the dependence of these demographic processes on fallow age and initial stand structure attributes was evaluated. In 11 secondary tropical rain-forest sites (1.5-19 y) in Chiapas, Mexico, one plot of 1.0 x 50 m was established. Diameter and height were measured for all trees >= 1 cm dbh, and their survival, growth and recruitment was monitored over a 2-y period. Changes in stand structure were especially fast in the first 5 y of succession, and decreased rapidly afterwards. which resulted from similar stand-level changes in relative mortality, growth and recruitment rates. Demographic processes were negatively related with initial stand basal area, but independent of initial tree density. Basal area was a better explanatory variable of the among-stand variability in these rates than fallow age. Results suggest that asymmetric competition and resulting patterns of tree-thinning are major driving forces determining secondary forest successional pathways. Fallow age per se is a compound variable reflecting community organization at a certain point along the successional axis, while community structure drives succession. Sudden mass mortality among dominant species in some stands showed that early secondary forest succession is not always a gradual and unidirectional process.