A large-scale inventory of two Amazonian tree communities
Department of Botany
2000
Thesis
Duke University
Durham, USA
Parque Nacional del Manu Cocha Cashu plants trees inventories large spatial scales ecology diversity beta-diversity latitudinal gradients Iriartea deltoidea abundance habitat preferences distributions habitat heterogeneity terra firme succession floodplains wetlands community structure Ecuador soils climate rarity palms Arecaceae, Myristicaceae Moraceae Violaceae forest structure Madre de Dios Bibliography
Two tree communities at the western margin of the Amazon basin were inventoried via networks of small plots scattered over several thousand square kilometers of forest. Yasunà National Park, Ecuador, is a moist, aseasonal, hyperdiverse lowland forest near the equator. Manu National Park, Peru, ~1,400 km and eleven degrees to the south of YasunÃ, is a moist, seasonal, moderately diverse lowland forest. The aims of the research were to document patterns of distribution, abundance, and diversity among Amazonian tree species at a variety of different spatial scales, and to investigate explanations for the patterns. The communities were surprisingly similar in composition and structure. Most species encountered in the inventories are believed to grow throughout western Amazonia, and a large proportion of them occur in both plot networks. Species common at one site tend to be common at the other, and the palm Iriartea deltoidea dominates both forests at identical densities. Most species in these forests occur preferentially in one forest type, but probably fewer than 15-26% of species are restricted to a single forest type. The great majority of species are rare at all spatial scales, but at both sites a small proportion of common taxa account for >50% of individual trees across the terra firme landscape. Common species tend to be large-statured trees, and are especially prevalent in the families Arecaceae, Myristicaceae, Moraceae, and Violaceae. The Ecuadorean forest is more diverse than the Peruvian forest at all taxonomic levels and all spatial scales. It also has a higher stem density, a larger proportion of smaller-statured species, a larger proportion of rare species, and higher-than-expected increases in the diversity of certain families. I argue that a large component of species composition and structure in these forests is homogeneous, and demonstrate that the tree communities in unvisited plots are largely predictable without any reference to local environmental conditions. However, I suggest that local processes related to the higher rainfall and higher stem density in Ecuador are more likely causing its higher diversity than large-scale or historical influences. Many of the observed patterns remain unexplained.