By Liz Kimbrough
The Bukit Tigapuluh landscape in Indonesia has been sliced and diced by roads, opening its forests to threats from the outside. As forest vanishes in the region, so too does its population of endangered Sumatran tigers.
A rapidly expanding road network in Asia threatens to usher in similar problems for tigers (Panthera tigris) elsewhere in Indonesia and beyond. According to a new study published in the journal >Science Advances, nearly 24,000 kilometres of new roads will be built in tiger conservation landscapes (TCLs) in Asia by 2050.
A Sumatran tiger (Panthera tigris sumatrae). Photo by Rhett A. Butler/Mongabay.
Using a recently developed global roads data set, University of Michigan conservation ecologist Neil Carter and his colleagues calculated the extent of planned and existing road networks across a 13-country range in Asia and the potential impacts of those roads to the globally endangered tiger. The analyses covered a nearly 1.16-million-square-kilometre (448,000-square-mile) range across Bangladesh, Bhutan, Cambodia, China, India, Indonesia, Laos, Malaysia, Myanmar, Nepal, Russia, Thailand and Vietnam.
"Our analysis demonstrates that, overall, tigers face a ubiquitous and mounting threat from road networks across much of their 13-country range," Carter said in a statement.
Tigers are listed as >endangered on the IUCN Red List, with fewer than 4,000 individuals still remaining in the wild. Tiger conservation has been flagged as a global conservation priority, and the international initiative >TX2 has set a goal of doubling global tiger numbers between 2010 and 2022 (China's next "year of the tiger.")
Road construction contributes to three major threats to tigers: degradation of habitat, prey depletion, and poaching.
Years after their construction, even low-traffic logging roads can increase human access to remote areas and contribute to the hunting and poaching of tigers and their prey. Tigers have also been >killed by vehicle collisions in India and elsewhere.
Royal Bengal tiger in Corbett National Park. Photo by Udayan Dasgupta/Mongabay.
In the Kerinci Seblat region of Sumatra, tigers >avoid public roads. This behaviour is suspected in other areas and represents a significant barrier to tiger movement, with the potential to isolate populations onto tiger "islands." The genetic variation that comes from tigers breeding with different populations is important to a resilient, healthy, and increasing tiger population. Maintaining wilderness corridors where tigers can move freely is of great concern to conservationists.
Areas of habitat that can support at least five adult tigers and where tigers have been spotted in the past 10 years are designated tiger conservation landscapes. The preservation of TCLs is considered crucial for the recovery of the species. Currently, 134,000 km (83,300 mi) of roads traverse the 76 known TCLs.
According to the study, these roads may be decreasing tiger and prey abundance by more than 20%, a finding that the paper calls "a highly troubling warning sign for tiger recovery and ecosystems in Asia."
The density of roads varies widely among countries and regions in the study. For example, the road density in TCLs in China was nearly eight times greater than in Malaysia. Out of the 10 TCLs found to have the highest road densities, two are considered global priority sites for tigers: the Bukit Tigapuluh landscape in Indonesia and Corbett-Sonanadi in India.
Between 2000 and 2012, Bukit Tigapuluh lost nearly 40 km2 (16 mi2) of forest due to the expansion of oil palm plantations. Over the same time period in that landscape, the number of adult tigers decreased from 36 to 22 individuals.