Invasive Acacia mangium dominance as an indicator for heath forest disturbance

Abstract

Heath forest ecosystems in Brunei are threatened as they are highly vulnerable to fire and converted for land development. On top of this, Acacia mangium, a non-native Australian tree species, has successfully invaded disturbed heath forest in Brunei. This species is now so common in disturbed heath forests that it shows potential as a disturbance indicator. To test this, we investigated how well Acacia dominance correlated with total basal area, canopy openness, species richness and stem density of heath forests. A total of 20 plots (400 ​m2 each) were established in heath forests with three different disturbance types; old-growth, old-regenerating and recent regenerating plots. Regression analyses were performed on Acacia dominance against the four variables. High Acacia dominance correlated strongly and positively with greater canopy openness but negatively with basal area, species richness and stem density. Acacia dominance was also strongly correlated with species composition. Our study finds that 1) Acacia mangium dominance can be used to determine the disturbance stage of heath forest, and as such provides an easy to measure indicator of heath forest health, and 2) that the most cost efficient way to eradicate Acacia mangium is fire prevention so that natural succession will provide the shaded conditions that prevent Acacia mangium establishment and population maintenance.