Rain Forest Structure at Forest‐Pasture Edges in Northeastern Costa Rica

Abstract

Land-use change in the Sarapiquí region of Costa Rica has resulted in a fragmented forest landscape with abrupt edges between forest and pasture. Forest responses to edge effects vary widely and can significantly affect ecosystem integrity. Our objective was to examine forest structure at 20+ yr old forest-pasture edges in Sarapiquí. Three transects with 0.095-ha plots at seven distances from forest edges were established in each of six forest patches. Stem density, basal area, and aboveground biomass in trees and palms ≥ 10-cm diameter at breast height were measured in all plots. In addition, hemispherical photographs were taken to determine leaf area index, understory light availability, and percent canopy openness. Linear mixed-effects models showed significantly higher tree stem density at forest edges, relative to interiors, a pattern reflected by increased stem density, basal area, and aboveground biomass in small diameter trees (≤ 20 cm) growing near edges. No differences in total tree basal area, aboveground biomass, or hemispherical photograph-derived parameters were detected across the forest edge to interior gradient. The recruitment of small diameter trees following edge creation has contributed to the development of dense vegetation at the forest edge and has aided in the maintenance of similar tree basal area and aboveground biomass between edge and interior environments. These data reflect on the robustness of forest edges in Sarapiquí, a characteristic that will likely minimize future detrimental edge effects and promote a number of high-value environmental services in these forests.Abstract in Spanish is available at http://www.blackwell-synergy.com/loi/btp.

Tree Responses to Edge Effects and Canopy Openness in a Tropical Montane Forest Fragment in Southern Costa Rica

“…Most studies on edge effects have typically investigated changes in canopy cover, various structural variables, and diversity and species composition across the forest edge-to-interior gradient [e.g. 6,14,16,17,19]. Few studies, however, have considered the disturbance regime-which contributes to reduced canopy cover inside the forest-as a factor contributing to overall physical and biological changes that can interact with edge effects [2,23,48].…”

“…The vegetation at the edges may seal the fragment laterally with a thick growth of thin stems and with the lateral growth of tree crowns [5,6]; but in the tropical lowlands, edges have also shown increased canopy tree mortality [7][8][9][10][11][12]. Edge-induced mortality of canopy trees would create additional gaps in the fragment's periphery, increasing canopy openness (a direct edge effect), and by increasing canopy openness, this could potentially and indirectly affect light penetration to the understory, which will alter the patterns of tree recruitment (indirect biological edge effects, sensu Murcia [13]).…”

“…Edge-induced mortality of canopy trees would create additional gaps in the fragment's periphery, increasing canopy openness (a direct edge effect), and by increasing canopy openness, this could potentially and indirectly affect light penetration to the understory, which will alter the patterns of tree recruitment (indirect biological edge effects, sensu Murcia [13]). This will ultimately affect the vegetation's composition and structure in the fragment's periphery [6,7,[14][15][16][17][18][19][20], extending to the forest interior in the case of small fragments (< 100 ha). Thus, canopy openness can be both part of a natural gap-dynamics cycle and, additionally, the direct manifestation of human edge effects.…”

Dinámica de paisaje en la Zona Norte de Costa Rica: implicaciones para la conservación del bosque tropical muy húmedo

“…Por otra parte, la fragmentación expone los organismos del bosque al efecto de borde (Lovejoy et al 1986), provocando el aumento en los niveles de luz, la invasión de organismos de áreas abiertas (Laurance et al 1985), procesos de sequía debido al efecto penetrante de los vientos (Laurance 1997) y cambios de características de la comunidad vegetal (Lovejoy et al 1997, Lezcano et al 2002. Sin embargo, una investigación en el área de estudio demuestra que los bordes de remanentes de bosque tropical húmedo se han recuperado después de dos décadas de estar expuestos a los efectos de la matriz circundante (Forero y Finegan 2002, Schedlbauer et al 2007. Un fragmento puede ser muy reducido en tamaño para proveer recursos alimenticios suficientes a los organismos de amplio rango hogareño, o puede soportar únicamente poblaciones pequeñas, las cuales son sujetas a altos riesgos de extinción por varios facto-res, incluyendo variaciones estocásticas del tamaño poblacional (Andersen et al 1997).…”

Connectivity of fragmented amphibian populations in a Neotropical landscape

“…In the study system, vegetation structure in forest is not strongly influenced by distance to the edge and forest-land use transitions tend to be very abrupt ( Fig. 1; Schedlbauer et al 2007). Enclosures were constructed out of light-wire mesh rolled into cylinders measuring 45 cm tall and 15 cm in diameter (e.g., ).…”