Seed deposition in the edge-interior gradient of a degraded fragment of tropical semideciduous forest, Northeastern Brazil

Abstract

The structure, dynamics and density of plant populations in different ecosystems are controlled by climatic seasonality. Seed rain contributes to both establishment and maintenance of the forest as well as to the recovery of disturbed areas near forest fragments. The aim of this study was to assess the deposition rate of different seeds of endemic and exotic tree species for the edge and for the interior of the forest matrix. The study area is a four hectares forest fragment located on the campus of the Federal University of Ceará. To measure seed rain, 80 collectors were suspended 20 cm above the ground in the gradient. Samples were collected monthly for 12 months (June 2009-May 2010), the material was screened in the laboratory and the diaspores (fruits and seeds) were quantified and taxonomically identified. We found 23 383 seeds belonging to 38 families and 89 different species, with a density of 134.48 seeds per m². The families Rubiaceae and Fabaceae were the most representative ones, with more quantities of seeds. The deposition of the seed rain was influenced by season and, consequently, by temperature and rainfall. There was a clear difference between the edge and the forest interior; with a large supply of native, animal dispersed and late successional seeds on the inside, and a considerable number of seeds belonging to non-native species and abiotic dispersion on the edge. Small fragments like this one can serve as important sources of seed for adjacent degraded areas, which demonstrate the importance of conservation and management of small fragments to avoid the degradation caused by edge effects. Rev. Biol. Trop. 63 (4): 981-994. Epub 2015 December 01.