Mounds of elephant droppings, giant liana vines twisting up through the trees, the morning chorus of siamang primates that amplify their songs by inflating sacs on their throats and towering dipterocarp trees that soar 170 feet (50 meters) above the earth: these are the stuff of a biologist’s dreams. And there I stood in awe and wonder, much as the fabled naturalist Alfred Russel Wallace must have felt when he studied the incredibly diverse rainforests of Sumatra more than a century ago.
It was the summer of 2009, and I was about to leave my native Taiwan to begin my doctoral studies at Texas Tech University. I had journeyed across much of Southeast Asia in search of a site for my dissertation research. I found it in the Bukit Barisan Selatan National Park (BBSNP) on this Indonesian island.
The park sprawls across 1,250 square miles (3,240 square kilometers), and it is designated, along with the Gunung Leuser and Kerinci Seblat national parks, as a World Heritage Site to highlight the forests and remarkable wildlife diversity of western Sumatra. Bukit Barisan Selatan is one of the last refuges for Sumatra’s remaining lowland rainforest. More than 90 terrestrial mammal species have been documented there, including critically endangered species of rhinoceros, tiger and elephant.
My first visit to the forest was enchanting, but what convinced me that it is where I should pursue my research was a distressing sight: vast robusta coffee plantations where rainforests and wildlife once thrived. An estimated 28 percent of the primary forest within the BBSNP has been replaced by illegal agriculture, primarily coffee plantations.
Coffee is one of the most important economic crops worldwide and has been cultivated commonly throughout tropical regions. Its export value is second only to petroleum among developing nations, with a total global trade value for 2003 of approximately US$100 billion. Vietnam and Indonesia are Southeast Asia’s leading coffee exporters and cultivated acreage has more than quadrupled in the past decade.
Coffee plantations are generally limited to tropical mountainous regions at elevations up to about 6,500 feet (2,000 meters) – where bat diversity is especially rich. Although this expanding coffee agriculture must impact bats in Southeast Asia, virtually no information is available about this potential threat. Studies on the impact of coffee agriculture on bat diversity have focused so far on Neotropical bats and arabica coffee plantations. Aribaca coffee, however, tolerates more shade and colder temperatures than robusta and the impacts on bats – good or bad – are likely to differ between the two. It is critical to the conservation of tropical bats to determine those potential differences.
My continuing research focuses on estimating bat-species richness across the Sumatran landscape and understanding how different bat species respond to coffee agriculture, with the goal of providing science-based recommendations to local agencies for conserving bat diversity across Bukit Barisan Selatan. But I also hope to demonstrate the economic and ecological values of bats to local farmers, particularly the economic potential of bat-discarded coffee beans and pest suppression by insect-eating bats.
I collaborated with Elly Lestari Rustiati at Indonesia’s University of Lampung and Meyner Nusalawo at the Wildlife Conservation Society-Indonesia Program. With financial support from Bat Conservation International’s Student Research Scholarships, I led a team of six University of Lampung undergraduate students and two Conservation Society field assistants to the national park from July 2010 to June 2012.
To explore the diversity of the park’s bats, we set harp traps and ground-level mist nets in both pristine and managed forests and in coffee plantations of two types: high-shaded and low-shaded. We also set mist nets across rivers and in the forest canopy, and used a stationary bat detector to monitor bats in such microhabitats as high, open-space above the canopy.
To date, we have confirmed 47 bat species in the Bukit Barisan Selatan National Park and adjacent coffee plantations. Furthermore, working with Mr. Maharadatunkamsi, Ibnu Maryanto and Sigit Wiantoro from the Museum Zoologicum Bogoriense, Indonesian Institute of Sciences, we identified another six species collected in the park by previous researchers. These results expanded the total number of documented bat species on Sumatra from 81 to 88.
Even more exciting, we found five groups of bats that we could not assign to any known species. These may quite possibly be undescribed species that are new to science, but more analysis is required to confirm that. Altogether, including another eight species from literature reviews, we reported a total of 61 species for the park and plantations – nearly two-thirds of Sumatra’s bat fauna. A preliminary analysis of the echolocation recordings suggests the possible presence of a few more species we may have missed during the surveys. That work continues.
The probable discovery of new species and evidence that this parkland is a bat diversity hotspot for Southeast Asia are certainly dramatic. But the more important results are the impacts that coffee agriculture is having on the diversity of bats in the national park.
After comparing capture data of 9 of our 12 study locations, I found that the impacts differ according to bat species’ different ecological traits. I classified species according to two ecological traits: diet (insectivorous and phytophagous, i.e., nectar/fruit-eating bats) and roosting ecology (plant-roosting forest bats, cave-roosting bats and generalists) because these traits are presumably correlated with habitat use.
My data told a sad story.
Among insectivorous bats, most plant-roosting species and some roost generalists were disappearing from the coffee plantations. These species are usually considered forest specialists in Southeast Asia and mainly include woolly bats (of the subfamily Kerivoulinae) and tube-nosed bats (Murininae).
In contrast, we found no difference among cave-roosting bat species, mainly Hipposideros and Rhinolophus species, among the varied habitats. Cave bats were dominant in most study sites regardless of habitat type, which highlights the importance of cave roosts in maintaining local bat diversity.
We did not detect any negative response of fruit and nectar bats to coffee agriculture. Instead, roost-generalist phytophagous bats, of the genus Cynopterus, were more abundant in high-shade coffee plantations than in forest.
A frequent goal of conservation biologists is to determine whether any tight correlations exist between certain species and various habitat types. Species that are highly correlated with natural habitats, such as rainforest, or disturbed habitats, such as coffee plantations, can sometimes be used as indicators of the level and type of human disturbance.
My data suggest that three species, all of them common throughout much of Southeast Asia, might be regarded as indicators in the park’s landscape. Lesser short-nosed fruit bats (Cynopterus brachyotis) were captured mostly within coffee plantations, while insect-eating Hardwicke’s woolly bats (Kerivoula hardwickii) and Trefoil horseshoe bats (Rhinolophus trifoliatus) were primarily limited to forests.
For example, confirming a Hardwicke’s woolly bat within a landscape where no bat surveys had been done might suggest the presence of undisturbed forest. Lesser short-nosed fruit bats, on the other hand, might indicate highly disturbed habitats. I hope to determine what is behind these species-habitat correlations – the availability of food or roost sites, perhaps, or direct disturbance by humans – and to use these species as indicators for all coffee/forest landscapes in this region.
These results indicate that robusta coffee plantations pose a significant threat to insectivorous bats that roost in trees and other plants. Protecting native forests is essential for their conservation, and preserving forested corridors that connect surviving woodlands would likely be very valuable. The protection of cave roosts in disturbed landscapes is absolutely critical.
My efforts to better understand just how coffee plantations affect bat diversity continues. We are also working to confirm the ecological and economic benefits that bats provide in these coffee-dominated landscapes in hopes of convincing local farmers of the wisdom of bat conservation. More studies of bats among coffee plantations and other agroecosystems are definitely needed to clarify whether our findings from the Bukit Barisan Selatan National Park represent a general pattern throughout Southeast Asia, and how we can help these invaluable mammals share these tropical forests with human farmers.
JOE CHUN-CHIA HUANG is a Ph.D. Candidate in the Department of Biological Sciences at Texas Tech University in Lubbock, Texas. His dissertation focuses on the diversity, ecological services and conservation of bats in Bukit Barisan Selatan Landscape on Sumatra, Indonesia.
The author thanks Dr. Tigga Kingston and Kendra Phelps for their help and advice with this research and its reporting.