Phenological and population responses of the invasive pioneer tree, Bellucia pentamera (Melastomataceae) to selective logging disturbance at Gunung Palung National Park, Indonesia
Gunung Palung National Park in Indonesia is currently an invasion front of the Neotropical pioneer tree, Bellucia pentamera, which has begun to establish in the last 10-20 years. Due to a period of intense selective logging that occurred outside the research station between 2000 and 2002 there is a sharp boundary between disturbed and undisturbed habitat in close proximity. Our goals were twofold: 1) determine the extent of the invasion and explore the effect of selective logging, and 2) document significant fruit output as an invasion mechanism of this fleshy-fruited animal-dispersed species.
We compared 70 plots in the disturbed area to those in the undisturbed research station, recording the presence of treefalls and evidence of prior selective logging activity. Sampled B. pentamera individuals were divided into four age classes: seedlings, saplings, juveniles, and adults to provide a rough estimate of population dynamics.
Monthly phenology was recorded for 12 months for individuals in both disturbed and undisturbed habitats to explore differences in fruiting frequency and crop size. These data were also used to make comparisons with native trees (in undisturbed habitat only) using phenology data that have been collected for other ongoing projects.
Plots with previous logging had significantly more B. pentamera individuals across all age classes than sites with treefalls alone, suggesting an important difference in the nature of these two types of disturbances. No individuals were found in plots without either logging activity or natural treefalls.
Phenology data suggest that B. pentamera is significantly more prolific in its fruit output than even the most frequently available native alternatives. For instance, while average stems of Pternandra spp. and Cyathocalyx spp. produced fruit in approximately 33% and 29% of survey months (respectively), mature stems of B. pentamera produce ripe fruit at a much higher frequency (75%). B. pentamera also produces fruit much more frequently in disturbed areas (80% of fruiting months) than in undisturbed areas (60%).
Our results suggest that without facilitation by selective logging, B. pentamera may well still have become naturalized, but may not have necessarily produced the significant invasion currently realized at Gunung Palung National Park. It appears selective logging has allowed B. pentamera to gain a spatial foothold that it is now able to continue to exploit by increasing reproductive output in these areas.