Leaf thickness and elevation explain naturalized alien species richness in a tropical mountain forest: a case study from Mount Gede-Pangrango National Park, Indonesia

Exotic plant invasion is one of the major causes of species extinction. In many contexts, mountainous forests are the last refuge for native species. There are several inventory studies conducted in mountainous and tropical forests in Indonesia. However, there are no studies yet on the factors that explain the abundance and richness of surveyed naturalized alien species. This study investigated whether the number of individuals and abundance-weighted species richness (AWR) of naturalized alien plant species in the hiking-trail of Mount Gede-Pangrango National Park (MGPNP) forest area correlated with leaf traits (specific leaf area (SLA) and leaf thickness) and environmental factors (elevation, slope, and normalized difference vegetation index (NDVI)). We showed that leaf thickness and habitat elevation explained the AWR variations of naturalized alien species. We did not detect any important effect of leaf traits and environmental factors on the number of individuals per exotic species per plot. The influence of leaf thickness and habitat elevation indicates the important role of both biotic and abiotic factors on exotic species to develop a high species richness and become an invasive species in the tropical mountain forest ecosystem.