Flooding gradient and treefall gap interactive effects on plant community structure, richness, and alpha diversity in the Peruvian Amazon

TitleFlooding gradient and treefall gap interactive effects on plant community structure, richness, and alpha diversity in the Peruvian Amazon
Publication TypeJournal Article
Year of Publication2010
AuthorsMyster, RW
JournalEcotropica
Volume16
Pagination43-49
Accession NumberLUQ.983
KeywordsBiodiversity, LTER, mass effects hypothesis, t amshiyacu ­t ahuayo, tahuampa, Terra firme, várzea, whitewater
Abstract

The Amazon is the most productive and diverse terrestrial ecosystem in the world and among its importantstructuring forces are flooding gradients and treefall gap dynamics. Consequently, in order to more fully understandAmazonian forests, I sampled Peruvian vegetation plots for five years both in forest and in fresh gaps within each of threeforest types (terra firme, varzea, tahuampa) that differed in flooding duration and maximum water depth. I found a signi-ficant effect of degree of openness (i.e. treefall gap formation) on canopy average height, canopy maximum height, basalarea, density, above-ground biomass, turnover, and alpha diversity, and a significant effect of forest type (i.e. the floodinggradient) on species richness, genera richness, density, turnover, and alpha diversity. In general, there were fewer trees, butthey were larger, and more productive in the forest plots compared with the gap plots; and the most flooded plots hadfewer trees, species, and genera compared with both the less flooded forest and unflooded forest. Also the greatest amountof turnover was found in the most flooded forests, and the intermediately flooded forest had the greatest richness and alphadiversity. These results taken together support a “mass effects” hypothesis where species from both the unflooded and mostflooded forests and their gaps have overlapping ranges in the less flooded forest and gaps, causing continuous immigrationwhich boosts diversity. In summary, (1) canopy structure was determined by traditional gap dynamics, but much of cano-py diversity depended on the type of forest, (2) tree density decreased as flooding increased, especially among the smalleststems, and (3) there was evidence to suggest that the high biodiversity of the Amazon may be maintained in part by theexistence of moderately flooded forest and gaps.