Plant Species Richness is Associated with Canopy Height and Topography in a Neotropical Forest

Jeffrey Wolf,Victoria Meyer,Thomas Gillespie,Geoffrey Fricker,Stephen Hubbell,Sassan Saatchi

doi:10.3390/rs4124010

Abstract

Most plant species are non-randomly distributed across environmental gradients in light, water, and nutrients. In tropical forests, these gradients result from biophysical processes related to the structure of the canopy and terrain, but how does species richness in tropical forests vary over such gradients, and can remote sensing capture this variation? Using airborne lidar, we tested the extent to which variation in tree species richness is statistically explained by lidar-measured structural variation in canopy height and terrain in the extensively studied, stem-mapped 50-ha plot on Barro Colorado Island (BCI), Panama. We detected differences in species richness associated with variation in canopy height and topography across spatial scales ranging from 0.01-ha to 1.0-ha. However, species richness was most strongly associated with structural variation at the 1.0-ha scale. We developed a predictive generalized least squares model of species richness at the 1.0-ha scale (R2 = 0.479, RMSE = 8.3 species) using the mean and standard deviation of canopy height, mean elevation, and terrain curvature. The model demonstrates that lidar-derived measures of forest and terrain structure can capture a significant fraction of observed variation in tree species richness in tropical forests on local-scales.

Highlights

At local-scales in tropical tree communities, species distributions are often correlated with differences in light, water, and nutrient availability caused by biophysical processes related to forest structure and topography [1,2,3,4,5]
The best model at 1.0-ha scale optimized by lowest AIC included the covariates mean and standard deviation of canopy height, mean elevation, and mean curvature (Table 1, Figure 2)
Past studies have shown that most plant species at local scales in tropical forests are associated with local-scale structural variation in canopy height and topography

Summary

Introduction

At local-scales in tropical tree communities, species distributions are often correlated with differences in light, water, and nutrient availability caused by biophysical processes related to forest structure and topography [1,2,3,4,5]. Species-level associations with environmental gradients are well documented at local-scales, there is limited information about how community-level patterns like species richness change in relation to structural variation in canopy height and terrain. The direct effect of gaps on fine scale (0.04-ha) species richness appears to be modest [9], but structural heterogeneity is likely to be a cause of variation in species richness due to some sorting of different species over gap-to-understory environmental gradients [1,11]. We evaluated whether and how species richness is related to canopy height and canopy structural heterogeneity

Methods

Results

Discussion

Conclusion