Microtopographic controls on lowland Amazonian canopy diversity from imaging spectroscopy

摘要

Microtopographic variation is ubiquitous throughout lowland Amazonia, and it may impart patterns of species richness and abundance, and perhaps community compositional changes. To date, no studies have determined the degree to which lowland microtopography influences forest canopy diversity. We developed the first high-resolution maps of forest canopy diversity in Amazonia, focusing on four landscapes on two river systems in Peru. Spectroscopic images were acquired using the Carnegie Airborne Observatory combined with a new method based on spectral species to map alpha- and beta-diversity. We analyzed spatial patterns in diversity with respect to floodplain and terrace (terra firme) surfaces and in upriver and downriver locations with contrasting landscape morphologies. We found slightly lower average alpha- diversity in floodplains, but with greater variance than in terrace communities caused by the floodplain mix of swamp forests, anoxic low-diversity ecosystems, and high-diversity areas. beta-diversity estimated with the Bray-Curtis dissimilarity (BC) was strongly related to microtopography, with floodplains showing higher internal compositional dissimilarity than terraces. Throughout all landscapes, remotely mapped BC within terrace environments ranged from 0.25 to 0.43, but these values increased 30-77% on floodplains. Upriver landscapes characterized by higher terraces showed more distinct community turnover than did their downstream counterparts. We conclude that microtopography strongly influences beta-diversity throughout the study landscapes, but terrain is weakly associated with variation in alpha-diversity. We uncover the importance of microtopography in determining species composition in lowland Amazonia and highlight the value of imaging spectroscopy for biodiversity research and conservation.