Plant diversity and structure of the Caimpugan peat swamp forest on Mindanao Island, Philippines

This investigation examined the species diversity and vegetation structure of the peat swamp forest on Mindanao Island, Philippines in relation to peat thickness, hydrology and physicochemical properties of soil and water. Sampling plots were randomly established along a relatively straight transect from the eastern side of the fringing tall pole forest towards the inner zone of pygmy forest, as well as in forest on the Kasawangan lakeshore in the western part of the peatland. The results showed that additional previously unidentified vegetation zones could be distinguished between the tall pole forest and the pygmy forest; i.e. tall intermediate forest and low intermediate forest. Statistically, these additional zones were strongly supported by analysis of variance on stand structure and by non-metric multidimensional scaling on peat properties. Moreover, a Lycopodium-Dicranopteris dominated plant community, which occurs arbitrarily as patches, was also observed. The tall pole forest was the most diverse forest type. In total, 101 species belonging to 56 families and 81 genera of vascular plants (trees and understorey vegetation) were recorded, with Tristaniopsis decorticata (Myrtaceae) and Thoracostachyum sumatranum (Cyperaceae) being the most dominant. Changes in forest structure from the outer to the inner zone are related to the increase in peat thickness towards the centre of the dome. The changes in structure are influenced by the shallow superficial peat layer and the protective surface layer of the peatland, the acrotelm.