Ecological role of vegetative sprouting in the regeneration of Dryobalanops rappa, an emergent species in a Bornean tropical wetland forest

Dryobalanops rappa (Dipterocarpaceae), a dominant tree in wetland forests in Borneo, often produces vegetative sprouts in its juvenile stages (trees less than 25 m in height), a characteristic that is believed to be rare in tropical forest trees. We investigated the growth characteristics of this species in a tropical forest in Merimbun Heritage Park, Brunei, to verify the hypothesis that the vigorous sprouting ability enables it to grow in a wetland forest with soft soils that promote stem decumbency and to assess the adaptive significance of vegetative sprouting in the context of its regeneration. Reproductively mature trees developed buttresses and were rarely decumbent. However, if they became decumbent, they died without sprouting. Juvenile trees were frequently decumbent, and their decumbent shoots sprouted vegetatively. Therefore, vegetative sprouting acted as a countermeasure to decumbency and death on the soft wetland soil. A decumbent shoot produced only one sprout in most cases. Decumbent shoots grew little and eventually died, but new sprouts showed rapid growth. This suggests that there is translocation of resources from decumbent shoots to sprouts. If decumbency occurs, a D. rappa genet ramifies into sprouts, and helps sustain the population in the wetland environment. This vegetative life history strategy is important for regeneration in wetland forests with soft soil.