Monday, November 29, 2010

Keeping Some of the Pieces, The Importance of Shade in Cacao Plantations

Cacao and coffee are shade crops that provide habitat for plants and animals dependent upon tropical forest. Unlike corn, they enhance biodiversity in agricultural landscapes locally but they may also have a more global role when they are cultivated in regions of high endemism suffering heavy deforestation. Sulawesi is one of those places that still conceals many undescribed species, but like many other places the forests are being logged and converted into human landscapes. Deforestation and subsequent land-use changes are rampant in the tropics and will eventually force the species that survive the upheaval to use altered habitats such as agro-ecosystems and urban areas that tend to be warmer, drier, brighter and less structurally complex than natural forests.
Southeast Asian amphibians and reptiles are among the most poorly studied and the most threatened vertebrates  (estimated at 30% and 31%, respectively based on IUCN 2008 data). Tropical amphibians and reptiles are highly sensitive to habitat modifications and climate change, making mitigating the effects of land-use change on herpetological diversity in Southeast Asia a conservation priority. Wanger et al. (2010) studied a land-use modification gradient ranging from primary forest, secondary forest, natural-shade cacao agro-forest, planted-shade cacao agro-forest, to open areas in central Sulawesi, Indonesia. They determined species richness, abundance, turnover, and community composition in all habitat types and related these to environmental correlates, including canopy cover and thickness of leaf litter. Human disturbances create environments that favor some species over others. Lizards and snakes for example, thermoregulate by basking in open patches of sun and it may be better to have several (or many) small openings in the canopy than just one large open patch. Therefore, many small openings in the canopy may be a better predictor for species richness and abundance of lizards. Frogs, on the other hand avoid direct exposure to the sun and a closed canopy may be a predictor of their diversity and abundance. Wanger and colleagues used Bayesian model selection to identify the best environmental predictors for amphibian and reptile species richness and abundance, including the lacunarity index (a measure of the degree of gaps) to measure canopy heterogeneity. Their results show that amphibians in Sulawesi were more negatively impacted by land-use changes than reptiles. Amphibian species richness and abundance declined as disturbance increased from pristine forest to open areas, while reptile species richness peaked in natural-shade cacao agro-forest between mildly (secondary forest) and strongly (planted-shade cacao agro-forest) disturbed habitats. Studies done in the Neotropics produced similar responses of amphibians and reptiles to disturbance in humid forests.  Thus conserving species of amphibians and reptiles in tropical environments may be best done long-term by allowing shade trees to rejuvenation on cacao plantations and allowing leaf litter to accumulate.

Wanger, T. C.,  D. T. Iskandar, I. Motzke, B. W. Brook, N. S. Sodhi, Y. Clough and T. Tscharntke. 2010. Effects of Land-Use Change on Community Composition of Tropical Amphibians and Reptiles in Sulawesi, Indonesia. Conservation Biology 24: 795–802.

No comments:

Post a Comment