Date Published: July 1, 2019
Publisher: Public Library of Science
Author(s): Erin E. Poor, Virta I. M. Jati, Muhammad Ali Imron, Marcella J. Kelly, Andrés Viña.
Worldwide, roads are a main driver of deforestation and degradation as they increase forest access along the forest edge. In many tropical areas, unofficial roads go unreported and unrecorded, resulting in inaccurate estimates of intact forested areas. This is the case in central Sumatra, which boasts populations of critically endangered Sumatran elephants (Elephas maximus sumatrensis), tigers (Panthera tigris sumatrae) and other endemic flora and fauna that make the area globally unique. However, maps do not reflect the reality of forest loss in the area. Here we present new maps from 2002 and 2016 of digitized and ground-truthed roads in one of Sumatra’s unique lowland tropical protected areas, Tesso Nilo National Park. Using our newly created roads dataset, we examine the distribution of forest with respect to distance to roads. Our data show >2,400 km of roads within the national park in 2016 –nearly a 10-fold increase from roads known in 2002. Most forest (82–99%) within Tesso Nilo falls within 100 m, 500 m, and 1000 m of road edges. Length of road increased 157% and road density increased from 1.06 km/km2 to 2.63 km/km2 from 2002–2016. Our results suggest that this endemic ecosystem is facing substantial threat from roads and their associated impacts. Without swift management action, such as road closures and increased enforcements by park management, this ecosystem, and its endemic wildlife, could be lost. It is imperative that protected areas worldwide more rigorously consider roads and road effects on ecosystem fragmentation in their conservation plans.
Globally, as forests are fragmented into smaller patches, biodiversity is lost directly as a result of forest clearing, and indirectly through increased forest access and illegal use of wildlife resources. In the Amazon, extinction rates are negatively correlated with area of forest fragments [1, 2] and fragments 0.01–0.1 km2 in size lose species across taxa at a higher rate than fragments 1 km2 or greater [3–6]. Furthermore, biodiversity is not only affected by the size of remnant forest patches, but also by the distance to, and habitat between neighboring forest patches, which can play roles in biodiversity persistence in a disturbed landscape [7, 1]. Thus, maintaining intact forested areas that are connected to other forested areas across a landscape is integral to maintaining global tropical biodiversity.
The decrease in forest within Tesso Nilo National Park due to roads and access trails increases the importance of natural forest areas outside of the protected area to provide habitat, corridors, and stepping stones for wildlife that face habitat loss within the park. It is widely recognized that Tesso Nilo has suffered from deforestation and degradation [37, 45, 46], but this is the first study in Indonesia that has quantified the effects of increases in road density on forest within a protected area. This research was motivated by receiving a roads dataset from the government of Indonesia that did not appear to reflect the on-the-ground situation, and we determined it necessary to create an updated and verified roads dataset. Furthermore, no previous research has focused on the impacts of human activity or roads in Tesso Nilo despite the declining populations of tigers  and elephants and the anecdotal evidence of recent increased human activity in the park. Given the evidence that apex predators and large vertebrates are the most disturbance-sensitive species in protected areas in the tropics , it is important to understand the impact roads have on multiple critically endangered species within Tesso Nilo, and to identify areas where impacts could be mitigated. We were unable to assess direct impacts to biodiversity during this study, but other studies have shown the negative impacts of road effects and human activity on tropical flora and fauna [8, 24, 29].