Publication

The composition, structure, and disturbance dynamics of the native oak forests in seasonally dry tropical highland regions throughout the world have been drastically altered due to human land use. Edge environments are a dominant feature in these highly fragmented landscapes, and may directly influence the capacity of the vegetation to ameliorate microclimate conditions and support the successful regeneration of disturbed habitat. In this study, microclimate variables (surface soil moisture, photosynthetically active radiation and ground, surface and air temperatures) were assessed across edge gradients occurring between forest remnants and openings of different sizes (<0.1 and >1 ha) in both a highly fragmented landscape and a relatively undisturbed adjacent landscape over a 2-year period. Surface soil moistures increased progressively from the open areas (10.8-40.1 g m(-3)) into the forest understory (16.8-54.7 g m(-3)). The steepness of the edge gradient was less pronounced in the highly fragmented landscape (23.02 g m(-3)) compared to the reference landscape (29.34 g m(-3)). These results suggest that microsite variability across edges was reduced in this landscape in response to fragmentation. Further, the occurrence of an extreme drought event during the second year diminished differences between the fragmented and reference landscapes, thereby leading to greater homogeneity of the microclimate across the edge environments. Structural differences in forest patches within the fragmented landscape were also found to interact synergistically with habitat fragmentation to influence patterns in microclimate across edge environments. The capacity of oak forests to ameliorate the availability and flux of surface soil moisture in seasonally dry tropical ecosystems through their effect on evaporative moisture loss, and the reduction of this buffering capacity in response to habitat fragmentation documented in this study, suggests that fragmentation has significantly altered the temporal and spatial heterogeneity of microclimate conditions in these landscapes. (C) 2003 Elsevier B.V. All rights reserved.