Doctoral Dissertation Research: Assessing and Modeling Forest Edge Effects and Habitat in Tropical Dry Forest of Upland Oaxaca, Mexico

Indiana University, Bloomington IN

Investigators

Abstract

Forest edges are areas of vulnerability and diversity that are distinct from interior forest in structure and function. The unique characteristics of forest-edge vegetation arise due to edge effects such as additional light, greater dryness, and increased risk of wind and fire damage. At broader scales, edge effects vary across ecosystems and are frequently associated with forest fragmentation, losses in biodiversity, and reduced spatial distribution of forest species. Edge effects in forest ecosystems have been studied primarily in tropical wet and temperate forests, but differential distances of edge effects are expected to exist for different forest types. This doctoral dissertation research project will develop empirical evidence to test the hypothesis that edge effects in tropical dry forest are different from edge effects documented in tropical wet forest. Edge effects in tropical dry forest are examined by synthesizing field, remote sensing, and geographic information system-based methods to determine the distance of edge influence for vegetation surrounding timber harvest clearings, develop methods to identify low-contrast edges associated with adjacent forest-management zones with different cutting schedules, and link vegetative edge response to bird distributions in a habitat model. The study area is in Oaxaca, Mexico. The Mexican tropical dry forest has a very high level of biodiversity and endemism, but little is known about edge influence on the system or the extent of edge influence. The Mexican tropical dry forest is important economically for timber production and other natural resources extraction, impacts that are also important from a forest management perspective. The study combines the remote sensing technique of spectral mixture analysis with geostatistics to identify and determine the distance of edge influence from a clearing to surrounding interior forest and to locate low-contrast edges. Multivariable statistics are used to determine relationships between vegetation structure and bird community composition in a spatial context. It is expected that edge effects in a tropical dry forest will be more subtle than in other forest types, particularly in the distance of edge influence and the actual responses to edge in vegetation and bird species. The results of this project should improve bird habitat inventories based on remote sensing, extend current applications of the remote sensing technique of spectral mixture analysis, improve understanding of tropical dry forest response to disturbance, and contribute to conservation and management of tropical dry forest ecosystems. Overall the project will improve methods that quantify land-use change effects on biodiversity by converting maps of forest cover to assessments of habitat. This research will contribute to scientific knowledge and reflect societal concerns by increasing the sparse understanding of how edges change tropical dry forests, addressing issues of forest and habitat loss, and improving the methods used to study forests. The results will be applicable to local management activities because they will describe the response of local forest bird populations to edge-affected habitat and provide information that is relevant to sustainable forest use and management in the study area. The methods developed for this project to determine the extent of edge effects are also expected to be useful to land managers in other parts of the world, where inexpensive forest and habitat assessments are needed. As a Doctoral Dissertation Research Improvement award, this award also will provide support to enable a promising student to establish a strong independent research career.