The direct and indirect impacts of roads on wildlife

A dirt road in the tropics. Image credit, Amilton Reis.Direct and indirect impacts of roads on wildlife...
It's easy to overlook the impacts that isolated roads can have on species in remote, natural areas. But a growing body of research in Europe and North America has shown that these types of roads can be especially problematic and need to be carefully considered by planners and managers.  In the tropics, where fewer studies have looked at these issues, road building has increased dramatically and its entanglement with local livelihoods and national economic development is creating very complicated problems. 

Two new studies offer interesting contrasts on the direct versus the indirect impacts that roads can have on species in the tropics. Direct impacts, which are usually pretty straightforward - occur when the road itself causes harm to wildlife - for example by serving as a barrier to movement. Indirect impacts - which are usually much more difficult to measure and address - occur when a road creates changes in the natural or social environment that in turn leads to negative impacts - for example in the case in which a road opens up an area to increased human exploitation.

Roads as a barrier to wildlife movement: the case of Cameroon...
A new study in the African Journal of Ecology looks at the direct impacts of roads in impeding wildlife movement. Researchers measured the probability that wildlife in Campo-Ma'an National Park would cross forest roads. They found that for the 6 of the 12 species groups that they studied, the presence of the road impeded their crossing. They determined this by looking at track plots for animals over a 17-day period along roads and along control areas in the forest interior. They compared the likelihood that wildlife crossed the plots on the roads versus the likelihood that they crossed the control plots in the interior. Tracks were most common for small mammals but they also found tracks for larger species like elephant and African Buffalo.

The researchers also correlated their findings of road crossing probability with specific road characteristics such as vegetation cover, proximity to the park entrance, physical obstacles, etc. Their goal was to find evidence of whether certain variables made roads more or less problematic for the crossing of different wildlife species. Of the variables that they analyzed, they found that physical obstacles along the road such as logs and deep trenches showed the greatest correlation with a lower probability of wildife crossing. 

Roads as an opening for increased human exploitation: the case of Ecuador...
In Ecuador, researchers from the Wildlife Conservation Society conducted a case study - appearing in the
journal Animal Conservation - that looked at the indirect impacts that the construction of a single road has Collared peccary. A common mammal hunted for bush meat in the Ecuadorian Amazon.
had by inadvertently spurring the growth of the bush meat trade. In 1992, Maxus Ecuador Inc. constructed a road that penetrates more than 140 km in Yasuní National Park in the Ecuadorian Amazon. Subsequent to construction several clans of Waorani people - a rainforest indigenous group that includes the last remaining nomadic people in Ecuador - abandoned their lifestyles, creating permanent settlements along the road. Also, after the construction, a nearby market for bush meat emerged. The researchers conducted interviews at the market and found that vendors and hunters sell without fear of impunity because of a lack of will of local officials to enforce regulations against bush meat.

The study authors conclude that the road has indirectly harmed wildlife by providing improved access for the hunting. They also conclude that the road has transformed the social environment of the local people - i.e. by breaking down their nomadic subsistence lifestyle and improving their access to markets - which has also let to increased hunting pressure on wildlife. The study points to the need for more research and resources to deal with the complex issues of indirect impacts of roads in the tropics.

--Reviewed by Rob Goldstein

Source:	African Journal of Ecology
Title:	Roadside conditions as predictor for wildlife crossing probability in a Central African Rainforest
Authors:	Christiaan van der Hoeven, Willem de Boer and Herbert Prins
	Wageningen University, The Netherlands

Source:	Animal Conservation
Title:	Oil industry, wild meat trade, and roads: indirect effects of oil extraction activities on a protected area in north-eastern Ecuador
Authors:	E. Suárez, M. Morales, R. Cueva, V. Utreras Bucheli, G. Zapata-Ríos, E. Toral, J. Torres, W. Prado & J. Vargas Olalla
	Wildlife Conservation Society, Ecuador