Effects of land use change and forest fragmentation on the biodiversity and ecosystem functioning in the lowlands of Sri Lanka

Abstract

Habitat disturbance caused by the rapid expansion of agriculture and anthropogenic land use severely impact native forest biota. Resulting changes in the environment include altered biotic community composition and ecosystem functions. The present study examines the effects of land use change and forest fragmentation on biodiversity and ecosystem functioning in Sri Lanka, using selected indicator taxa. The study was conducted in the lowland wet zone, the most species-rich zone of Sri Lanka, but which has been severely affected due to logging and conversion to agriculture and home gardens. Throughout the study, selected modified land use types; old selectively logged forest, monoculture plantations, home gardens and forest fragments, are compared with primary forests to evaluate the effects of habitat disturbance. The selected indicators; Amphibians, butterflies and Scarabaeinae dung beetles, are globally known to be among the best indicators of habitat disturbance due to their sensitivity to habitat changes. To examine effects of anthropogenic land use and selective logging, the diversity and community composition of amphibians and butterflies followed by dung beetles were surveyed using standard sampling techniques. We found that amphibians, specially endemics and direct developing species were more susceptible to habitat modification than butterflies in the lowland wet zone landscape. The environmental determinants of the communities indicated that structural variables of the habitats were more important for amphibians, while butterflies communities were more responsive to climatic variables. The diversity and abundance of Scarabaeinae beetles were assessed in multiple land use areas over a wide geographic range and twenty forest fragments in the lowland wet zone. Prior to this, the dung beetle fauna of Sri Lanka was surveyed to re-establish the taxonomy and the study reported 117 species island wide. We found that diversity and abundance of dung beetles negatively responded to anthropogenic land use in tea plantations and home gardens, primarily through altered abundance and community composition; total species richness was less affected. Communities in more than 70% of forest fragments were significantly different from the primary forest and those differences were best explained by fragment area, area to edge ratio and some abiotic and structural environmental variables (i.e. soil temperature, soil pH, maturity of the forest indicated by DBH profile). Dung beetle community parameters were related to ecosystem functioning by quanifying dung removal across the same gradient of land-use change as a measure of the impact of disturbances on and nutrient recycling. Dung removal was negatively affected by land use change, primarily through altered abundance and functional group diversity. Here we discuss the importance of restoring nutrient enrichment of soil through dung removal, and the potential economic benefits for agriculture. This study provides the most coherent picture to date of how amphibians, butterflies, and mostly Scarabaeinae dung beetles are affected by land use change and forest fragmentation in Sri Lanka, and how ecosystem functioning of dung beetles is influenced by habitat modification. In addition, the study surmounts some of the hurdles to tropical conservation research by supplementing the limited knowledge on ecological effects of habitat disturbance in South Asia specifically by highlighting an ecologically little known country in the region. The research findings can be used to make scientifically informed recommendations for the conservation of pristine forests and management of anthropogenic land use areas to increase their conservation value.