Species composition and phylogenetic diversity in a tropical peat swamp forest, Central Kalimantan, Indonesia

Abstract

Tel/Fax:+81-89-946-9775 ABSTRACTThe catenary sequence of vegetation in tropical peat swamp forest has been attributed to reduced nutrient availability along the gradient of peat depth. The objective of this study was to assess the phylogenetic structure of tropical peat swamp forest vegetation with the aim of clarifying the community assemblages. We laid out six plots along the gradient of peat depth in the upper catchment of the Sabangau river, Central Kalimantan, Indonesia and investigated forest phylogenetic structure. We found a tendency for phylogenetic diversity to decrease as peat depth increased. Higher phylogenetic diversity in the forest zone closest to the river could be attributed to competitive exclusion in a relatively benign peatland environment, whilst lower phylogenetic diversity further from the river could be attributed to the filtering effect of a more stressful environment. There was, however, unexpected low phylogenetic diversity in the tall interior community in the Sabangau forest, where environmental conditions were less extreme. This observed low phylogenetic diversity is possibly related to the history of peat development and degradation in this location as the ombrogenous peat is undergoing long-term oxidation due to reduced precipitation and lowering of the water table. We conclude that not only environmental filtering but also biotic filtering through such mechanisms as competitive exclusion contribute to the catenary sequence of tropical peat swamp forest vegetation.