UC Davis

In tropical rainforests, gaps created by fallen canopy trees are the primary colonization sites for pioneer species. Selective logging mimics these natural disturbances in that only a single tree is felled, creating a gap of comparable size. Rates of tree felling greatly exceed natural mortality rates, however, changing disturbance regime by increasing the number of gaps in logged areas compared to intact forest. Little is known about whether gaps in logged forests are qualitatively different as well. At Gunung Palung National Park in West Kalimantan, Indonesia, a period of selective logging in areas adjacent to the research station created a natural experiment permitting comparison of populations of the invasive pioneer tree Bellucia pentamera in selectively logged and undisturbed forest. We sought to first establish whether canopy gaps are necessary for invasion by B. pentamera. We then examined whether the type of gap (logging vs. natural treefall) had an effect on recruitment. Finally, we compared populations in natural treefall gaps in logged and undisturbed forest to estimate the effect of logging on population size. Bellucia pentamera was limited to gaps, regardless of canopy tree density. Furthermore, gaps created by selective logging supported significantly more B. pentamera individuals than natural gaps. Finally, natural treefall gaps in the disturbed area contained significantly more individuals than gaps in the undisturbed forest. Therefore, it appears that selective logging not only created more gaps for B. pentamera, these gaps in particular promoted greater abundance of this invader and led to a population increase throughout the disturbed habitat.