Edge Effects of Linear Canopy Openings on Tropical Rain Forest Understory Microclimate

Abstract

We investigated microclimatic edge gradients associated with grassy powerlines, paved highways and perennial creeks in wet tropical forest in northeastern Australia during wet and dry seasons. Photosynthetically active radiation, air temperature and vapor pressure deficit, soil temperature, canopy temperature, soil moisture, and air speed in the rain forest understory were measured during traverses perpendicular to the forest edge. Light intensity was elevated near the edges of powerlines, highways, and creeks, but this effect was strongest for creek edges. Air temperature and vapor pressure deficit were elevated near powerline edges in the dry season and highway edges in both wet and dry seasons but were not elevated near creek edges in either season. In contrast, soil moisture was lowered near creek edges but not near either powerline or highway edges. No edge gradients were detected for air speed. Canopy temperature was elevated near highway edges and lowered near powerline edges in the wet season but no edge gradients in canopy temperature were detected near creek edges in either the wet or the dry season. We suggest that these different edge gradients may be largely the result of differences in the fluxes of latent and sensible heat within each type of linear canopy opening, with periodic flood disturbance assisting by maintaining a more open canopy near creek edges. Our data indicate that the nature of the linear canopy opening is at least as important as the width in determining the nature and severity of microclimatic edge effects, analogous to the “matrix effect” of traditional fragmentation studies.

Understorey vegetation gradient in a Eucalyptus grandis plantation between a savanna and a semideciduous forest

“…These differences were more pronounced than could be explained solely by increased light near the edges of the study site (Bowering et al 2006;Delgado et al 2007;Pohlman et al 2007). Time since establishment is a plausible alternative explanation.…”

Landscape Attributes Drive Complex Spatial Microclimate Configuration of Brazilian Atlantic Forest Fragments

“…However, the intensity/magnitude and the spatiotemporal nature of these edge-mediated shifts may be highly variable and modulated by a set of patch and landscape metrics, such as fragment location, edge characteristics, plant-stand attributes, and biotic factors [4]; however, these shifts have been proposed to invariably express themselves as edge-microclimate gradients. Collectively, these edge-interior gradients are believed to produce an internal belt of harsh environment, i.e., a more illuminated, desiccated, and windexposed habitat, which parallels forest edges [33]. Such an environment, although highly sensitive to changes of edge vegetation structure and temporarily inconstant [35], is likely to persist as long as forest edges border open-habitat matrices [36].…”

Pathways affect vegetation structure and composition in the Atlantic Forest in southeastern Brazil

“…Different widths can determine the degree of microclimatic changes in the edge zone of a pathway (Pohlman et al 2007). Light availability, high temperatures, low relative humidity, variation in soil nutrient availability and sediment runoff are variables that change according to the characteristics of linear gaps (Reid & Dunne 1984;Denslow 1987).…”