Abstract
BackgroundEdge effects cause changes in bird community richness, abundance, and/or distribution within a landscape, but the avian guilds most influenced can vary among regions. Although Southeast Asia has the highest rates of deforestation and projected species loss, and is currently undergoing an explosive growth in road infrastructure, there have been few studies of the effects of forest edges on avian communities in this region.MethodsWe examined avian community structure in a dry evergreen forest in northeastern Thailand adjacent to a five-lane highway. We evaluated the richness and abundance of birds in 11 guilds at 24 survey points on three parallel transects perpendicular to the edge. At each point, 10-min surveys were conducted during February‒August 2014 and March‒August 2015. Vegetation measurements were conducted at 16 of the bird survey points and ambient noise was measured at all 24 survey points.ResultsWe found a strongly negative response to the forest edge for bark-gleaning, sallying, terrestrial, and understory insectivores and a weakly negative response for arboreal frugivore-insectivores, foliage gleaning insectivores, and raptors. Densities of trees and the percentage canopy cover were higher in the interior, and the ambient noise was lower. In contrast, arboreal nectarivore-insectivores responded positively to the forest edge, where there was a higher vegetation cover in the ground layer, a lower tree density, and a higher level of ambient noise.ConclusionPlanners should avoid road development in forests of high conservation value to reduce impacts on biodiversity. Where avoidance is impossible, a number of potential mitigation methods are available, but more detailed assessments of these are needed before they are applied in this region.
Highlights
Edge effects cause changes in bird community richness, abundance, and/or distribution within a landscape, but the avian guilds most influenced can vary among regions
Edge represents distance to forest edge, D0 is stem density of vegetation with height between 0.5–3 m, C0 is percentage cover of vegetation at < 0.5 m, and C5 is percentage cover of vegetation at 5–10 m a Indicates estimated coefficients of variables that had a significant influence on avian guild richness and abundance our hypothesis that edge effects influenced at least some avian guilds differently and that certain groups, including understory, sallying, terrestrial, and bark-gleaning insectivores, were observed to be higher in richness and abundance in the forest interior
While it is difficult to extrapolate the effects of forest edges on avian communities from one relatively small study area and one type of edge to other forests, this is the first detailed study of the edge responses of birds in Southeast Asia, and the only study to investigate a roadside edge
Summary
Edge effects cause changes in bird community richness, abundance, and/or distribution within a landscape, but the avian guilds most influenced can vary among regions. Southeast Asia has the highest rates of deforestation and projected species loss, and is currently undergoing an explosive growth in road infrastructure, there have been few studies of the effects of forest edges on avian communities in this region. Edges alter the physical environment of forest habitats via increased sunlight, temperature extremes, and wind exposure, and reduced humidity, directly influencing vegetation structure and food availability, which may, in turn, cause changes in the avian community. Such changes may render edge habitats unsuitable for some bird species (Murcia 1995). Roadside edges change the physical environment, and lead
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