Floristic composition across a climatic gradient in a neotropical lowland forest

Abstract

Abstract. This study deals with the floristic composition of lowland tropical forest in the watershed of the Panama Canal. The floristic composition of large trees in 54 forest plots was analysed with respect to environmental factors, including precipitation, geologic parent material, stand age, topography, and soils. The plots contain 824 species of trees with a diameter at breast height ≥10 cm and represent a regional flora with exceptional β‐diversity. Plot data indicate that the Panamanian forest is strongly spatially structured at the landscape scale with floristic similarity decreasing rapidly as a function of inter‐plot geographic distance, especially for distances <5 km. The ordinations and patterns of endemism across the study area indicate broad floristic associations well correlated with Holdridge life zones. The results indicate the positive aspects of life zone classification at regional scales, while simultaneously highlighting its inadequacy for finer scales of analysis and resource management. Multivariate gradient analysis techniques (Non‐metric Multidimensional Distance Scaling and Detrended Correspondence Analysis) show clear patterns of floristic variability correlated with regional precipitation trends, surficial geology, and local soil attributes. Geologic and edaphic conditions, such as acidic soils or excessively drained limestone substrates, appear to override the effects of precipitation and modify forest composition. We conclude that the Panamanian forest shows clear patterns of spatial organization along environmental gradients, predominantly precipitation. The rapid decline in floristic similarity with distance between stands also suggests a role for dispersal limitation and stochastic events.

Influência da distância geográfica na riqueza e composição de espécies arbóreas em uma Floresta Ombrófila Densa na Amazônia Oriental

“…Com o aumento da distância há um decréscimo na similaridade ambiental entre locais, formando gradientes de condições ambientais (Nekola & White 1999). Nestes casos as comunidades são estruturadas pelo nicho, e a distribuição das espécies de plantas está relacionada à distribuição heterogênea dos fatores ambientais no espaço (Pyke et al 2001;Zumquim 2007).…”

Causes of habitat loss in a Neotropical landscape: The Panama Canal corridor

“…We calculated mean annual rainfall for each subregion from the ACP data (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003). Rain gauges from the ACP were not available for all subregions, therefore we interpolated precipitation data from isohyets available from atlases; these data were concordant with other studies in the same area (Condit, 1998;Pyke et al, 2001;Santiago and Mulkey, 2005;Rompre et al, 2007). Variability in elevation was determined by calculating maximum altitude above sea level (ASL) in each subregion minus minimum altitude (ASL), which was often the altitude of the canal waters.…”

“…For example, forest bird species richness increases from 4 dry-forest specialists to more than 170 wet-forest specialists along this gradient (Ridgely and Gwynne, 1989;Angehr, 2006;Robinson et al, 2004;Rompre et al, 2007). The same pattern occurs in tree species richness (Condit, 1998;Pyke et al, 2001). …”

“…Presently, more than 1.3 million people currently live in the study area. Biodiversity increases from the Pacific to the Caribbean along a steep rainfall gradient (Condit, 1998;Condit et al, 2001;Pyke et al, 2001). For example, forest bird species richness increases from 4 dry-forest specialists to more than 170 wet-forest specialists along this gradient (Ridgely and Gwynne, 1989;Angehr, 2006;Robinson et al, 2004;Rompre et al, 2007).…”

“…Mean annual precipitation data were obtained from the Panama Canal Authority (ACP) and atlases (see also Condit, 1998;Pyke et al, 2001). We calculated mean annual rainfall for each subregion from the ACP data (1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003).…”