Vegetation structure and composition along an interior-edge-exterior gradient in a Costa Rican montane cloud forest

A study was carried out in the Costa Rican Cordillera de Talamanca in order to assess changes in vegetation structure and floristic composition along a gradient from the interior of tropical upper montane cloud forest into ad jacent pastureland. At four sites a 150 x 10 m belt transect was establishe d perpendicular to the forest/pasture edge. Vegetation transect censusing i ncluded recording of seed plane species presence and abundance (aerial crow n/shoot cover), as well as assessment of seedling sapling and tree stem dia meter and height. A total of 290 seed plant species were found in 159 gener a and 85 families. Asteraceae is with 47 species the most speciose family. Shannon-Wiener's diversity index showed no significant difference between f orest and pastureland, with the exception of a pastureland site which had e xperienced intensive land use. Sorensen's similarity index showed significa nt differences in species composition between forest and pastureland. Veget ation at the forest edge consisted mainly of secondary shrub and tree speci es. From the forest interior towards the edge, numbers of seedlings, saplin gs and secondary trees increased, while numbers of mature forest trees decl ined. Edge effects are expressed in a reduction of canopy height and an inc rease in subcanopy stature from the forest interior towards the edge, causi ng thr merging of forest canopy and subcanopy layers at the edge. Intensive ly used pasturelands only harboured a low herbaceous vegetation, while thei r abandoned equivalents showed the presence of patches of secondary shrub v egetation and recovering forest in a grassland matrix. Expected spatio-temp oral changes at the forest edge include the encroachment of secondary veget ation and the levelling of the forest/pasture border as time advances and l and use becomes less intense. Transitional second,growth edge vegetation ma y buffer the remaining mature forest core and simultaneously induce forest recovery processes in adjacent abandoned pasturelands. It is recommended to include forest edge tree species in programs focused at the ecological res toration of tropical montane cloud forests. (C) 2000 Elsevier Science B.V. All rights reserved.