Open Woodland Patches in an Evergreen Forest of Kampong Thom, Cambodia: Correlation of Structure and Composition with Microtopography

Open woodland patches scattered in dense evergreen forest are a landscape peculiar to Kampong Thom Province. One of these open woodland patches was studied by setting a belt transect, and floral composition, stand structure, and habitat conditions were examined. Based on a census for trees 10 cm or greater in diameter at breast height (DBH), the forest along the transect was divided into three types that varied with topography. Most of the area was covered by gentle slopes and was dominated by Dipterocarpus obtusifolius, which displayed 50% canopy openness and poor species richness. The stands were located on rectilinear to convex sloping sites with low clay content that were waterlogged in the rainy season. Melaleuca cajuputi stands occurred in a small swamp, whereas on the slope M. cajuputi was mixed with D. obtusifolius. The M. cajuputi stands were geographically isolated from the coastal location more characteristic of the species. Along the stream or beside the swamp, where no waterlogging occurred even in the rainy season, we found Vatica odorata stands. Physical habitat conditions associated with the topography, such as clay content and soil water conditions, enable the three forest types with different physiognomies to coexist at this small spatial scale and may also explain the outpost patches of M. cajuputi.