Seed rain in areas with and without bamboo dominance within an urban fragment of the Atlantic Forest

Maria Tereza Grombone-Guaratini,Luciana Ferreira Alves,Daniella Vinha,Geraldo Antônio Daher Corrêa Franco

doi:10.1590/s0102-33062014000100008

Abstract

Understanding the flow of diaspores is fundamental for determining plant population dynamics in a particular habitat, and a lack of seeds is a limiting factor in forest regeneration, especially in isolated forest fragments. Bamboo dominance affects forest structure and dynamics by suppressing or delaying the recruitment of and colonization by tree species as well as by inhibiting the survival and growth of adult trees. The goal of the present study was to determine whether dominance of the bamboo species Aulonemia aristulata (Döll) McClure in the forest understory influences species abundance and composition. We examined the seed rain at two noncontiguous sites (1.5 km apart) within an urban forest fragment, with and without bamboo dominance (BD+ and BD- areas, respectively). Sixty seed traps (0.5 m², with a 1-mm mesh) were set in the BD+ and BD- areas, and the seed rain was sampled from January to December 2007. Diaspores were classified according to dispersal syndrome, growth form and functional type of the species to which they belonged. There were significant differences between the two areas in terms of seed density, species diversity and dispersal syndrome. The BD+ area showed greater seed density and species diversity. In both areas, seed distribution was limited primarily by impaired dispersal. Bamboo dominance and low tree density resulted in fewer propagules in the seed rain. Our results suggest that low availability of seeds in the rain does not promote the maintenance of a degraded state, characterized by the presence of bamboo.

Highlights

Landscape fragmentation and the loss of habitat are widespread processes in the modern world and represent one of the most import threats to global biodiversity (Laurance et al 2001)
In one year of seed rain collection, we identified a total of 54 morphospecies, representing 38 genera and 25 families (Tab. 1)
The diaspores most frequently found in the seed traps in the BD+ area were from the species Mikania cordifolia, Asteraceae sp. 1 and Piptocarpha oblonga, while only Asteraceae sp. 1 and M. cordifolia were frequently recovered in the BD− area

Summary

Introduction

Landscape fragmentation and the loss of habitat are widespread processes in the modern world and represent one of the most import threats to global biodiversity (Laurance et al 2001). Recent studies have identified the effects of landscape fragmentation on several natural processes, including changes in seed flow due to an overall reduction in dispersal agents (Melo et al 2006). Within this context, knowledge on the dynamics of urban forests, where the effects of human disturbance have a greater impact, could provide information on how to manage such forest fragments (Burley et al 2008). According to Burley and contributors, dependence on allochthonous sources is exacerbated in urban fragments isolated from potential seed sources, resulting in the establishment of non-native species and the dominance of individual native species that are potentially favored by natural disturbances (2008)

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