Document: KER-3-40-30

Impact of nonnative plants on native tree diversity and composition in Madagascar.

BROWN, K.A.*

State University of New York at Stony Brook, Stony Brook, NY 11794 USA ¹

Abstract:
A survey of eight forest stands in low montane rainforests in Madagascar was performed to ascertain how the proliferation of non-native plants affects native plant communities. Stands studied were either selectively logged and abandoned ~50 years ago, clear-cut and abandoned ~150 years ago, or have not been logged and are relatively undisturbed. Species diversity indices (Shannon index and Simpson index), species accumulation curves (calculating Smax), and ordinations (Non-metric Multidimensional Scaling, NMS) were used to compare the vegetation in the three forest types. Possible confounding effects of elevation and disturbance history were separated using partial Mantel tests. Invasive plants were found to be most abundant and dominant in logged sites. Diversity measures for both types of logged stands were lower than for unlogged stands. Species accumulation curves revealed a similar pattern, with the ~50 and ~150 year logged sites maintaining an average asymptotic estimated true species richness (Smax) of 37 and 38 species per 900 m² respectively, while the unlogged sites have an average Smax of 55 species per 900 m². The first ordination axis was strongly associated with logging history. The partial mantel tests revealed that invasive plants were more commonly found at more disturbed sites, regardless of plot altitude (or elevation). Logged forests in Madagascar appear not to be recolonized by native species after disturbance, at least not within 150 years after initial disturbance. Moreover, the survey provides some evidence that the recolonization of native plant communities is somewhat inhibited by the establishment and dominance of nonnative plants.

Keywords: Shannon index, Simpson index, Non-Metric Multidimensional Scaling (NMS), partial Mantel test, Species accumulation curves, invasive plants.

This abstract is being presented at: 3:30 PM in session:
Poster Session #17: Vegetative Analysis.