Knowing the hill forest on the west slopes of Gunung Palung from my thesis research at the Cabang Panti Research Station many years ago, I have been looking forward to seeking differences in tree composition in this valley. Most of the valley’s forest occurs on ridges and slopes of granite-derived sandy soils (see this paper by Chuck Cannon & Mark Leighton). However, around our camp there is also some lovely, flat alluvial forest, at an elevation of 230 meters. An area of very hard rock (a basalt dike?) underlies the valley a half kilometer downstream from our campsite, creating a high waterfall called Riam Parit. This block seems to have ‘dammed’ the erosional deposits in the valley above, creating a surprisingly large area of flat, fertile alluvium.
Low-elevation alluvial forests near the big rivers of Borneo are the most diverse on the island and contain the biggest trees, and are also the first to be converted to agriculture. It will be interesting to see if this slightly higher elevation alluvial forest, isolated from the true alluvial forests, contains any of the tree species typical of these forests. My first impression, as we set up our first 50 square meter inventory plot on Friday, is that most of the species on this alluvium are typical of granite hill forest, but are those requiring higher nutrient sites. However, some species (e.g., Dipterocarpus tempehes) are seldom found in hill forest and must be small, relatively isolated populations. As soon as we have marked out the six survey plots (three in alluvium and three on the drier hills), we’ll begin assessing the species composition to provide a better idea of what is growing here. Stay tuned.