Do environmental attributes, disturbances and protection regimes determine the distribution of exotic plant species in Bangladesh forest ecosystem?

Introduction of exotic plant species in the tropics has occurred since the colonial period, and has mostly been for timber production. However, due to uncontrolled distribution and lack of awareness, many of these species became invasive, and have been increasingly reported as a source of threats to native ecosystems. We investigated the exotic species richness, their traits, and biogeographic origin in the Satchari Forest in the north-eastern region of Bangladesh, one of the very few intact terrestrial ecosystems remaining in the country. Boosted Regression Trees and Detrended Correspondence Analysis were performed to determine the contribution of various environmental attributes, protection regimes, and disturbances to explain the distribution of exotic species within Satchari Forest. Among the environmental variables, native species richness, elevation gradient, and soil nutrient parameters were found as good predictors of both exotic species' presence and richness in the area. In our analysis, number of exotic species showed a unimodal relationship with native species in the reserved forest, where the relationship was negative in the surrounding area. An increase in exotic species with the presence of higher anthropogenic disturbance events, thereby with lower conservation restrictions as well as with lower protection status, was also evident. Our study suggests that enforcing greater protection status and preventing human use can be the best ways to protect native species composition in forest ecosystems with greater conservation values in tropical developing countries. (c) 2013 Elsevier B.V. All rights reserved.