Tree species diversity and distribution in a forest plot a Yasuní National Park, Amazonian Ecuador
The local species richness of woody plants is extremely high in northwest Amazonia. In a single hectare, trees with a diameter at breast height (dbh) ≥ 10 cm may number over 300 species and shrubs and treelets may contribute greater than 50% of the vascular plant species in 0.1- and 1.0-ha plots in western Amazonia. In this chapter, we present results from a 2-ha plot that comprises 787 species of trees and shrubs ≥ 1 cm dbh.
How so many species can coexist in a small area is still an open question. Many theories explain the high diversity found in small portions of tropical rainforests. One of these, the niche differentiation hypothesis, suggests that because each species uses resources in a different way, coexistence occurs when resources vary spatially, and each species occurs where it is a superior competitor. Consistent with the niche differentiation hypothesis, Tuomisto and Ruokolainen found that fern and Melastome species have distributions restructed to different topographic habitats in Amazonian forests. In this paper we analyze the patterns of shrub and tree diversity in 2 ha that contain two main topographic habitats: ridge and bottomland. We then asked two questions related to niche diversification: 1) How much diversity can be attributed to niche-partitioning across the habitat boundary? 2) How much diversity can be attributed to the partitioning of forest by different life forms (shrubs, treelets, canopy trees)?