| Vast areas of lowland tropical rainforest have been converted to anthropogenic grasslands by the synergistic effects of logging, agriculture, and recurring fire. These degraded areas are susceptible to colonization by invasive species. In Borneo, which has experienced the highest levels of deforestation among all the humid tropics of the world, degraded areas are at risk of being colonized by native plant species that act as invasives and that impact forest reestablishment. Here, I define such plants as "colonizing invasives," native species that are not usually found in undisturbed ecosystems but that have the ability to establish and develop dense stands in disturbed areas. In Tanjung Puting National Park, my study area, the dominant colonizing invasives are a grass, Imperata cylindrica, and two ferns, Dicranopteris linearis and Pteridium aquilinum. To understand the ability these colonizing invasives to infest disturbed ecosystems or and to predict future changes in anthropogenic settings, I conducted a critical examination of early succession after fire on repeatedly burned forests. To test the hypothesis that site age, fire-frequency history, and climate affect succession in Imperata- and fern-dominated areas, I took repeated measurements of soil properties and several indicators of vegetative succession in a chronosequence of permanent plots with different fire-frequency histories. The analyses, which included PCA, mixed effects modeling, and hurdle modeling, indicated that areas with a history of high fire frequency had more colonizing invasives, fewer total plant species, and less seedling recruitment. Furthermore, high fire-frequency areas were more susceptible than areas with a history of lower fire frequency to changes in soil chemistry. The results of this study illustrate the need to prioritize areas for reforestation based on use- or fire-frequency history.;In an effort to develop low-input reforestation techniques for areas with a history of high-fire frequency, I tested the effects of root exclusion on the growth and survival of four native tree species. The analyses included survival analysis and mixed and linear modeling. Root exclusion did not have any effect on the survival or growth rates of the seedlings, but two species showed great potential for use in reforestation: Schima wallichii and Syzygium laxiflorum.;In summary, this dissertation illustrates that despite the slow successional patterns of areas with a history of high-fire frequency, it may be possible to employ low-cost, large-scale reforestation techniques with native tree species. In addition, the results of this dissertation may be used to: (1) explore whether ecosystems currently dominated by colonizing invasives can be restored to native secondary forest; and (2) make future prediction about successional patterns to prioritize areas for reforestation. |
