Research of forest succession and animal seed dispersal in Thailand and prediction of future changes in tropical forests of Southeast Asia

Here I present two topics of my researches conducted in Thailand (1) forest succession (2) animal seed dispersal, and imply these results to predict future changes in the tropical forests of Southeast Asia.
Deforestation has been a major driver of tropical forest succession worldwide including Southeast Asia for many decades, as a result, humans depend more or less on ecosystem services of these regenerated or second-growth forests. In temperate regions, classification of forest succession and relevant theories have been well developed for using as a benchmark to understand underlying processes along a gradient of succession. However, classification in many studies of tropical forests are usually subjective and lagged behind. As a result, it is difficult to conduct a cross-comparison research among different tropical areas. Using the field data collected in Khao Yai National Park, Thailand, we apply a perspective of the dynamical system to demonstrate the framework for forest classification requiring only three variables of forest-structure. Additionally, the results of the analysis of crown architecture and community composition of trees in the same area are compatible with expectations from the predictions of a theory from temperate forests. The analysis of species composition also shows distinction of species assemblage in each stage. In the current era of forest protection and agribusiness (e.g. oil-palm and rubber plantation), secondary forests may be a rare habitat in Southeast Asia in the future, which landscapes may have only old-growth forests (well protected forests) and agricultural plantation.
Seed dispersal by large-bodied frugivores, particularly primates, can help to maintain tree diversity in tropical forests. Defaunation is a critical global problem, and the most severe in Southeast Asia. Although many studies show negative impacts of defaunation on tree diversity, most of them concentrate on the early life stages such as seeds or seedlings, not many on larger-size classes. We apply the spatial-point pattern analysis, namely “individual species–area relationship” and use the results to conduct a new analysis with the binary data (+ or 0) on the seed dispersal network at the Mo Singto plot to test the hypothesis that the major primate frugivores, rather than other arboreal frugivores, generated patterns of locally increased species richness around their preferred diet species (i.e., accumulator effects) in sapling and adult trees. Our results suggest that primates are major drivers of contagious seed dispersal which generate species-rich seed rain around their preferred food-tree species, which results in significantly larger local species richness of saplings. Defaunation of large-bodied frugivores may erode future biodiversity of Southeast Asia.