Demography of palm species in Brazil’s Atlantic forest: a comparison of harvested and unharvested species using matrix models

Abstract

Surprisingly little is known about the effect of alternative harvesting methods and different means of reproduction on the population dynamics of plant species. Here, we test the hypothesis that habitat fragmentation leads to negative population growth rates for three palm species in Brazil’s biodiversity-rich and highly fragmented Atlantic forest. We compared the demography (λ and elasticities) of Astrocaryum aculeatissimum, Euterpe edulis and Geonoma schottiana in five fragments ranging in size from 19 to 3500 ha. A total of 4.05 ha were censused throughout the landscape studied. All individuals of the three palms were tagged in 2005 and their survival was monitored in 2006 and 2007. All new plants were also recorded. Summary matrices were constructed for each transition years by pooling data from all plots of all fragments together for each species. Based on summary matrices, A. aculeatissimum and G. schottiana asymptotic population growth rates were not significantly different from 1, suggesting that populations of these palms were stable. The projection of E. edulis populations was to decrease in size, with 95% confidence intervals of λ for these estimates failing to exceed one in the second transition year. A. aculeatissimum, E. edulis and G. schottiana survivorship was high for all stage classes and exceeded 85% for postseedling stages. We found that the more important vital rates were the survival rates in larger stages for all three species. Our results show that the maintenance of high levels of reproductive survivorship should be a focus of conservation strategies for these species, especially in the case of large E. edulis individuals.