CANOPY OPENINGS, SEED GERMINATION, AND TREE REGENERATION IN MALAYSIAN COASTAL HILL DIPTEROCARP FOREST

Studies were conducted in coastal hill dipterocarp forest of Malaya to determine: (1) effects of treefall gaps on forest microclimate, (2) the influence of gap size on tree seed germination, (3) the influence of light on the seedling growth of shade-tolerant and shade-intolerant species, and (4) what factors influence the distribution of tree seedlings in natural forest gaps.; Two treefall gaps had higher irradiance, consistently higher surface-soil and air temperature, less soil moisture during dry periods, and more variable microclimates than did closed-canopy forest. Observed changes were greater in the larger gap.; Only six of the 42 species investigated germinated well in closed-canopy forest, forest gap, and large clearing environments. Some species required dense forest shade for complete germination, others required large canopy openings. Both pioneer and shade-tolerant species germinated in the gap, but the germination of most shade-tolerant species was dramatically reduced in the large clearing.; Seedlings of Parishia insignis grew well at 15% and 65% full sun; Trema tomentosa seedlings grew only in the sunniest site. Six-month-old Trema seedlings were twice as tall and had a biomass 2.7 times greater than Parishia seedlings grown in the high-irradiance site.; Plot axis scores derived from detrended correspondence analysis of seedling abundance data were correlated most strongly with elevation, canopy coverage, the number and size of competing trees, and soil disturbance. No species were restricted to forest plots, but several species appeared only in gaps. Type of disturbance was less important in determining gap composition than was the composition of the pre-gap vegetation.