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Tropical forest recovery: Establishment of an invasive tree in Puerto Rico.
Brown, Kerry*,1, Scatena, F.2, Gurevitch, Jessica1, 1 SUNY at Stony Brook, Stony Brook, NY2 University of Pennsylvania, Philadelphia, PA
ABSTRACT- Over the past century, tropical forests have been subjected to numerous types of anthropogenic-induced disturbances. In some cases, forests have been allowed to regenerate. However, our knowledge of post-disturbance regeneration of tropcial systems is sparse. We investigated the long-term ecological consequences of sites affected by different past land-use histories in the Luquillo Experimental Forest (LEF). We relied upon historical classification maps to help reconstruct the extent, cover, and forest type for our study areas in 1936. We categorized our field sites based on the total forest cover in 1936: <10% cover, unforested; 20-50% cover, secondary forest; 50-80% cover, secondary forest; 50-80% cover, native forest. Analysis of the vegetation patterns suggests that recolonization of unforested sites and regeneration in secondary forests were disproportionately affected by Syzygium jambos establishment. Spearman's coefficient of rank correlation revealed that S. jambos density and Shannon's diversity were significantly, negatively correlated. Forests that were most disturbed in 1936 were more highly invaded and exhibited lower diversity measures. Although the diversity measures for sites with elevated S. jambos densities were less than those with lower densities, there were no observable patterns between asymptotic species richness and S. jambos density. There was a significant, positive correlation between S. jambos density and soil phosphorous and nitrogen pools. Our results suggest that the disturbance regime of over fifty years ago has helped to shape present day forest recolonization and vegetation patterns along riparian and upland valleys in LEF. Habitats that were most disturbed in 1936 were predisposed to nonnative plant colonization and establishment, mostly by S. jambos. And presently, those sites exhibit depressed diversity measures, highest Syzygium densities, and larger Syzygium basal area, suggesting that this plant is not a transient component of the forest community. Although S. jambos is strongly associated with a reduction in plant species diversity, its presence has apprently not displaced any particular species. The plant's high density simply seems to decrease the space available for establishment of heterospecific individuals.
Key words: plant invasion, forest regeneration, Syzygium jambos