Tropical forest management altered abundances of individual tree species but not diversity

Abstract

In this study, we evaluated tree species abundance distribution in a Brazilian Amazon forest following reduced-impact logging and unlogged plots over two decades. A large body of literature shows changes in species abundance distributions (SADs) after disturbances in many systems and suggests that SADs are a useful tool for monitoring community recovery after impacts. We used Poisson lognormal distribution to described SAD, which has sigma and correlation parameters, for comparing species diversity before logging and over time. Sigma is a measure of alpha diversity and correlation expresses similarity between communities. Contrary to our expectations, we detected no changes for sigma, but correlation showed a decreasing trend, particularly after the first decade. Those changes were due to the increase in the abundance of pioneers and little recruitment of commercial species. Mortality was mainly attributed to the accidental death of non-targeted individuals. Because of the dominant role of random accidental tree deaths, the signature of logging operations was not detected immediately after logging using sigma. Forest management did not cause changes in the abundance structure of communities if we disregard species composition. However, considering species composition, and particularly, which species were common or rare, we did detect changes over time. The trends we have detected might be an early warning of a stronger long term tendency, which could affect abundance distributions. Due to the long lifecycle of trees and their slow growth rate, longer-term studies are needed to understand the impacts of logging on tropical forests.