|Cartoon from here.|
Over the past couple of posts I've been discussing the "road problem" at Kerinci Seblat National Park. Currently there are at least 32 proposals that would penetrate the interior of the park. In the first post I talked about why people want roads. In the second post I described how the lack of roads impacts residents of Kerinci valley while simultaneously suggesting that additional roads might not be the best solution to the problem. Today I'm going to look at the ecological impacts of roads. Though as an impartial and neutral researcher I have no dog in the fight, I do think it's important that policymakers have as thorough an understanding of what's at stake before making far-reaching and irreversible decisions. Most people are not aware of the multitudinous ways that roads alter the environment. From the actual surface itself to the "road corridor" (the road surface plus maintained roadsides and any parallel vegetated strips) to the interior several hundreds of meters away from the road itself, the road trace shapes the surrounding environment in obvious and not-so-obvious ways.
|Deforestation associated with new roads in Amazon basin. From Mongabay.|
Lesser-known Impacts of Roads on Animals and Plants...
The most conspicuous direct impact of roads is on certain large wildlife species. Specifically at TNKS conservationists worry about how the roads will affect one of the last remaining populations of Sumatran tigers, which are very endangered (1). Tigers are what ecologists refer to as an "interior species"; this means that they avoid the edge areas of forests. They also need large "patches" of forest to thrive. The construction of roads fragments the habitat and thus divides the tiger population into smaller populations. The tigers won't cross the road to find mates, and in the long run these smaller populations are much more vulnerable to extinction than one large, contiguous population. Avoidance behaviors have many different causes; traffic noise, visual disturbance, pollutants, and predators moving along the road have all shown to contribute. This is known as the barrier effect. Roads also affect tiger livelihoods; Kerley et al (2002) showed that Amur tigers living in roadless areas stayed longer at kill sites, ate more meat, and thus lived healthier and survived longer than tigers living near roads.
Roads have species-specific effects which also vary depending on location, traffic, and road conditions. For example, one study showed that moderately traveled tropical roads (as opposed to heavily-used roads) have higher incidents of roadkill for amphibians and reptiles. Possibly related to this is the fact that blacktopped roads absorb a great deal of solar radiation, re-radiating it at longer wavelengths as thermal energy. In other words, the road gets hot, which attracts animals like reptiles that use the external environment to regulate their body temperature.
The Edge Effect...
|Diagram from Proust Bushland Services|
Other Ecological Effects
|From Chicago Wilderness Magazine|
As you can see, there is a lot more to the road than meets the eye. Researchers have learned much about the ecological impacts of roads, but there is still a tremendous amount of research to be done. Much of the lessons of roads have been learned via experience. Australia, the US, and the Netherlands are all countries where the impacts of roads have been studied after the fact. Hopefully other countries, including Indonesia, can utilize this experience for better policy making.
(1) Estimates as to the number of Sumatran tigers remaining range from around 300 to 1000. According to recent research, Kerinci Seblat is the biggest remaining habitat for the tigers and has the highest numbers.
(2) Roads also helped the spread of fire ants, which were introduced to the US in the 1930s in Mobile Alabama. Though the ants can thrive in any habitat, they are most often found within 150 meters of roads.
References and For Further Reading....
Coffin, Alisa. 2007. From Roadkill to Road Ecology: A Review of the Effects of Roads. Journal of Transport Geography 15, pp396-406
Forman, Richard. 2003. Road Ecology: Science and Solutions. Washington, D.C.: Island Press.
Forman, Richard and Lauren Alexander. 1998. Roads and Their Major Ecological Effects. Annual Review of Ecological Systems 29, pp207-31
Kerley, Linda, John Goodrich, Dale Miquelle, Evgeny Smirnov, Howard Quigley, and Maurice Hornocker. 2002. Effects of Roads and Human Disturbance on Amur Tigers. Conservation Biology 16:1 pp97-108.