Factors determining the modes of tree death in three Bornean rain forests

Mode of tree death in relation to topography was examined in three lowland rain forests Belalong and Andalau, in Brunei Darussalam and Danum, in Sabah, East Malaysia. In total, 1543 dead trees greater than or equal to 20 cm diameter at breast height (DBH) were enumerated in an area of 36 ha. In Belalong, 31 % of the dead trees had died standing, 26 % had snapped, 21 % had uprooted, 19% had either died-standing or snapped and 3 % remained undetermined (n = 436). In Andalau, 46%, had died standing, 11% had snapped, 14 % had uprooted, 26 % had either died standing or snapped and 3 cic remained undetermined (n = 591). In Danum, 37 % had died standing. 22 % had snapped, 14% had uprooted, 24 % had either died-standing or snapped and 3 % remained undetermined (n = 516). Slope position. e.g. whether the tree was located in a valley, mid-slope. upper slope or ridge, was related to mode of death in all three sites. Elevation and tree diameter were related in two of the sites, and drainage, soil depth and soil shear strength were related in one of the sites. Generally the proportion of standing deaths increased moving from the valleys up to the ridge tops while uprooting proportions had the converse relationship. Slope position had little effect on the proportions of snapped trees. The three modes of death create different types of gaps. The findings substantiate that different topographies have different proportions of these gap types. The predominant gap type may have consequences for local and regional differences in forest structure and composition.