Landscape-scale forest loss shapes demographic structure of the threatened tropical palm Euterpe edulis mart. (Arecaceae)

Abstract

The expansion of human activities has led to drastic changes in the original landscapes in which tropical forests stand, causing the loss and fragmentation of natural habitats. Both processes induce changes in forest structure and local microclimatic conditions that are important modulators of the survival and demographic structure of plant species. The Neotropical palm Euterpe edulis Mart. (Arecaceae) is a keystone species largely consumed by several animals. Nevertheless, such emblematic species has also been over-harvested for palm-heart extraction, which led it to be currently classified as vulnerable to extinction. Understanding the main predictors affecting its persistence in forest remnants is essential for proposing strategies to modify this current scenario. In this context, we aimed to investigate how processes occurring in two different spatial scales (i.e. forest cover at the landscape scale and local microclimatic conditions) affect the demographic structure of E. edulis. We selected 20 forest fragments along the Brazilian Atlantic Forest in southern Bahia, embedded within landscapes ranging from 10 to 98% of forest cover amount. In each fragment, a plot of 100 × 50 m was established and all individuals of E. edulis were counted. A datalogger was also deployed in the center of the fragment to collect data of air temperature and relative local humidity. We used a zero-altered negative binomial regression (ZANB) to investigate the influence of forest cover and microclimate variables on the demographic structure of E. edulis. A total of 6528 individuals distributed in the five ontogenetic stages was recorded, with Juveniles presenting the highest number of individuals. Forest cover, not microclimate, was the best predictor of the demographic structure for all ontogenetic stages. We suggest that deforested areas are also more prone to palm harvest, which might explain the pervasive effects on the species persistence. We strongly recommend the maintenance and restoration of forest areas to ensure the maintenance of current populations of this endangered palm species. Yet due to the species overexploitation, reintroducing the species to already depleted fragments is urgently required along the Atlantic coast, combined with an increase in surveillance and environmental education programs to curb illegal extraction in highly deforested areas.