Publication
 

Influence of edge exposure on tree seedling species recruitment in tropical rain forest fragments

ABSTRACT Edge creation has a pronounced influence on the understory vegetation, but the effects of edges on seedling species recruitment are still poorly understood. In Central Amazonia, 9-19 years after fragmentation, we recorded species richness and net seedling recruitment rate in 1 ha blocks exposed to none, one, or multiple edges within forest fragments. One-hectare blocks were located in the center (no edge), the edge (one edge), the corners (two edges) of 10 and 100 ha fragments, and in a 1 ha fragment (four edges). In 1991, we counted all tree seedlings 5-100 cm tall found within permanent 1 m2 plots located within the 1 ha blocks. In May 1993, we manually removed all seedlings that were smaller than 1 m tall from the permanent plots. Six years and five months later (October 1999), all new seedlings recruited into the plots were counted and classified into distinct morphospecies. Species richness of recruited seedlings, scaled by total seedling density, declined from the center to the edge, the corner blocks, and then to the 1 ha fragment. Overall, the four-edged, 1 ha fragment had the poorest species richness and the non-edged 100 ha central block the highest. The total number of recruited individuals was 40 percent less than that previously present, with the 100 ha corner having the lowest recruitment. Pairwise comparisons showed that species similarity was related to edge number for the 100 and 1 ha fragments. Species rank/abundance curves showed that a subset of species was common in all blocks within the fragments, and that the 100 ha center held more rare species than any other 1 ha block. This study demonstrated that, in a given fragment patch, the number of tree seedling species recruited varied inversely with the number of edges.
RESUMO A formaao de bordas influencia drasticamente a vegetaao de sub-bosque, mas os efeitos sobre o recrutamento de especies de plantulas ainda sao poucos conhecidos. A riqueza de especies e a taxa de recrutamento de plantulas na Amazonia Central em um periodo de 9-19 anos depois da fragmentaao foram quantificadas em parcelas de 1 ha expostas a uma, nenhuma e varias bordas dos fragmentos. Estas parcelas de 1 ha foram distribuidas no centra (sem borda), na borda (uma borda), na esquina (dois bordas) de fragmentos de 10 e 100 ha e em um fragmento de 1 ha (quatro bordas). Em 1991, contamos todas as plantulas de especies arboreas, de 5 a 100 cm de altura dentro das parcelas permanentes de 1 m2. Seis anos e cinco meses depois (1999) todas as plantulas novas recrutadas foram contadas e classificadas em morfoespecies. A riqueza de especies de plantulas recrutadas foi maior no centra, seguida de bordas e depois de parcelas de esquina de fragmentos de 10 e 100 ha. O fragmento de 1 ha apresentou a menor riqueza de especies e a parcela central de 100 ha a maior. O numero total de individuos recrutados foi 40 por cento menor que o quantificado anteriormente e o menor recrutamento foi observado na esquina do fragmento de 100 ha. Comparaoes pareadas evidenciaram que a similaridade de especies se relaciona com o numero de bordas para os fragmentos de 100 e 1 ha. As curvas de amplitude/abundancia de especies demonstrou que determinado grupo de especies era comum em todas as parcelas de todos os fragmentos, sendo que o centra do fragmento de 100 ha apresentou, comparativamente, mais especies raras. Este estudo demonstrou que quanto maior o numero de bordas em um fragmento, menor o numero de especies de plantulas arboreas recrutadas.

Authors: 
Benitez-Malvido, Julieta Martinez-Ramos, Miguel
Journal: 
Biotropica
Year: 
2003
Volume: 
35
Issue: 
4
Pages: 
530-541
Site: 
Manaus