Responses of woody plant seedlings to edge formation in a lowland tropical rainforest, Amazonia

Abstract

Forest fragments surrounded by pasture are likely to be influenced by edge effects. This paper describes short-term effects of edge creation on woody seedling dynamics in an Amazonian lowland rainforest, using data collected between nine months before and 16 months after creation of an abrupt forest-pasture edge. Starting in December 1989, recruitment, mortality, and growth of plants ≤250 cm tall were monitored in plots located in the interior and at 5, 10, 25, 50, 100 and 250 m from the edge of a 100-ha forest fragment. In each plot, temperature and relative humidity were measured three times, while hemispherical photographs were taken after edge creation to estimate vegetation cover. Seedling recruitment increased along transects at 5 and 10 m from the edge following edge creation; pioneer species (especially Cecropia spp.) were recruited up to 10 m from the edge where they had previously been absent. Seedling mortality did not increase following edge formation. Seedlings within 10 m of the edge exhibited accelerated vertical growth, with a logarithmic decline in the effect with distance from the edge. Increased vertical growth was most pronounced for plants recruited at about the time of edge formation. Temperature and vapor pressure deficit were elevated following edge formation to ca. 50 m into the forest, and both declined exponentially with distance from the edge. Over the first 15 months following edge creation, recruitment and growth of woody seedlings was increased only up to 10 m from new edges, and mortality was unchanged, suggesting that the edge effect for woody seedlings was only about 10 m wide.