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

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 growt h of plants less than or equal to 250 cm tall were monitored in plots locat ed in the interior and at 5, 10, 25, 50, 100 and 250 m from the edge of a 1 00-ha forest fragment. In each plot, temperature and relative humidity were measured three times; while hemispherical photographs were taken after edg e creation to estimate vegetation cover. Seedling recruitment increased alo ng transects at 5 and 10 m from the edge following edge creation; pioneer s pecies (especially Cecropia spp.) were recruited up to 10 m from the edge w here they had previously been absent. Seedling mortality did not increase f ollowing edge formation. Seedlings within 10 m of the edge exhibited accele rated vertical growth, with a logarithmic decline in the effect with distan ce from the edge. Increased vertical growth was most pronounced for plants recruited at about the time of edge formation. Temperature and vapor pressu re deficit were elevated following edge formation to ca. 50 m into the fore st, and both declined exponentially with distance from the edge. Over the f irst 15 months following edge creation, recruitment and growth of woody see dlings was increased only up to 10 m from new edges, and mortality was unch anged, suggesting that the edge effect for woody seedlings was only about 1 0 m wide. (C) 1999 Elsevier Science Ltd. All rights reserved.