PARENT SESSION
Poster Session 39: Late Breaking and Newsworthy Posters
Friday, August 12, 8:30 AM - 10:30 AM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal
Restricted zones of influence reduce competition among rainforest tree seedlings.
Paine, C. E. Timothy*,1, 2, Harms, Kyle1, 1 Louisiana State University, Baton Rouge, LA, cpaine3@lsu.edu2
ABSTRACT- Ecologists have long held that resource competition structures most plant communities. Individual plants engage in resource competition only if their zones of influence overlap and at least one resource, the availability of which the individuals can affect, is in short supply. Seedlings in closed-canopy forests are suppressed by asymmetrical resource competition with canopy trees, but they may fail to compete among themselves because of their low density and small stature. We tested this hypothesis with field-grown even-aged monodominant stands of seedlings of Matisia cordata (Bombacaceae), a common canopy tree in the rainforests of Western Amazonia. We determined the extent of above- and below-ground zones of influence of individual seedlings, and the degree to which they overlapped with those of their neighbors. We also determined the intensity of intraspecific cohort competition in stands of M. cordata seedlings in a clipping experiment. Aboveground zones of influence overlapped more than belowground (1.7, 77.1% and 4.5, 9.6%, respectively [median, 95th percentile]). Even among nearest neighbors, the distribution of zone-of-influence overlaps was highly skewed, with a few large overlaps and a long tail of non-overlapping individuals. We failed altogether to detect intraspecific competition; neither seedling growth nor survival differed significantly among clipping treatments. The mean density of M. cordata seedlings in our study plots was five times greater than the mean density of seedlings of all woody dicots at six sites throughout the Neotropics. This comparison, together with our failure to detect competition in high-density stands, suggests that seedlings in closed-canopy rainforests frequently fail to compete. Should individuals fail to compete within cohorts, the consequences could be profound at the population and community levels. Size alone would govern ranking in competitive hierarchies. Individual performance would be decoupled from population density. All species capable of tolerating the shaded understory of the tropical rainforest could potentially coexist.
Key words: Matisia cordata, resource competition, tropical trees, Peru