Floristic composition of a neotropical forest across a climatic gradient in lowland Panama

TitleFloristic composition of a neotropical forest across a climatic gradient in lowland Panama
Publication TypeThesis
Year of Publication1999
AuthorsPyke, CR
Thesis Typephd

This study investigated the composition of large trees within a lowland forest in the watershed of the Panama Canal. Fifty-four 1-ha plots inventoried by the Smithsonian Tropical Research Institute were analyzed with respect to environmental factors, including: precipitation, geologic parent material, stand age, topography, and soils. The 54 plots represent a regional flora with exceptional beta diversity and low floristic nestedness. The plot network contains 821 species of trees with a diameter at breast height greater or equal to 10 cm. For comparison, the well-studied 50-ha forest dynamics plot on Barro Colorado Island in the middle of the isthmus contains 303 species of large trees. The Panamanian forest is strongly spatially structured at the landscape-scale with floristic similarity decreasing rapidly as a function of inter-plot geographic distance. Polythetic, agglomerative cluster analysis, in combination with non-metric multidimensional distance scaling ordination, and relative rates of species accumulation indicate broad floristic associations well correlated with mapped Holdridge Life Zones. Multivariate ordination techniques (non-metric multidimensional distance scaling and Detrended Correspondence Analysis) show strong patterns of floristic variability correlated with regional precipitation trends and local soil attributes. Geologic and soil conditions, such as acidic soils or excessively drained limestone substrates, appear to override the effects of precipitation and modify forest composition. The analysis of forest assemblages with respect to these environmental parameters suggests possible opportunities for increased conservation efficiency. Exceptional soil conditions identified in this study sometimes juxtapose dissimilar forest types over relatively short geographic distances. These localities provide opportunities for significantly increasing relative rates of species accumulation through informed site selection. The identification of these soil complexes through fieldwork, remote sensing technologies, and geographic databases represents a significant opportunity for future research.