Initial study of a new tropical plant invasion by the Neotropical pioneer tree, Bellucia pentamera (Melastomataceae), at Gunung Palung National Park, Indonesia

Background/Question/Methods

         Tropical plant invasions have most commonly occurred in disturbed areas, such as forest gaps and riparian zones, where the “lottery” of colonization tends to supersede otherwise niche-based competition in determining species success. For animal-dispersed gap plant species, those that consistently produce large quantities of fruit may therefore be particularly successful.

            Gunung Palung National Park in Indonesia is currently an invasion front of the Neotropical pioneer tree, Bellucia pentamera(Melastomataceae), which has begun to establish in canopy gaps and along riparian corridors in the last 10-20 years. This species produces large sugar-rich fruits, dispersed by birds and arboreal and terrestrial mammals. As there have been no prior systematic studies of this invasion, our first efforts have been focused on survey work at the park as well as gathering phenology data to estimate the seed output capabilities of this invasive gap tree.  

            Preliminary surveying of B. pentamera populations involved measuring stem density and DBH to provide demographic information to accompany initial population estimates. We also compared the reproductive behavior of B. pentamerato other common animal-dispersed tree species in established phenology plots in order to get a preliminary indication of its potential presence in the seed rain.

 Results/Conclusions

          Preliminary survey results indicate that B. pentamerais quickly colonizing available space along rivers and in treefall gaps. Areas experiencing higher disturbance (due to selective logging) in particular are showing rapid population expansion in less than 10 years.       

           Phenology data suggest that B. pentamera is significantly more consistent in its fruit output than even the most frequently fruiting native trees. For instance, while average individuals of Pternandra (Melastomataceae) and Cyathocalyx (Annonaceae) produce fruits in approximately 29 - 33% of survey months, early observations suggest mature individuals of B. pentameraproduce ripe fruits at a much higher frequency (over 50%). There is also variation in crop size between disturbed and undisturbed areas, with individuals in former logging gaps producing more fruit.

            While this invasion is still in its early stages at Gunung Palung National Park, it appears that the ability of B. pentamera to consistently offer fruit to dispersers may be one of the factors leading to its rapid spread. Furthermore, selective logging may be leading to increased individual fecundity, in addition to simply increasing population density.