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.
Literature
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.
Labels: biodiversity, conservation, herpetofauna, plantations, shade