Roads harm rainforest species

James Cook University, Science Alert 26 Oct 09;

Infrastructure such as roads, canals, power lines and gas lines could be the biggest threat for the world’s tropical rainforests, according to scientists at James Cook University and the Smithsonian Institution.

“Clearing wide paths in any forest has a strong effect on the ecosystem, but these impacts are particularly acute in tropical rainforests,” said Professor William Laurance, a biologist at the Smithsonian’s Tropical Research Institute in Panama and recently appointed as a Distinguished Professor at James Cook University.

Professor Laurance coauthored a paper on the impact of roads in the journal Trends in Ecology and Evolution with Dr Susan Laurance and Dr Miriam Goosem.

Dr Laurance is also a biologist from the Smithsonian and a Senior Lecturer in JCU’s School of Marine and Tropical Biology. Dr Goosem is Principal Research fellow in JCU’s School of Earth and Environmental Sciences.

Dr Goosem said the team used dozens of existing studies done in the Amazon, Australasia and Central Africa to emphasize that roads are the number one threat to the world’s tropical rainforests.

“We believe that maintaining large areas of intact forests without roads should be highest priority of conservationists worldwide,” she said.

Biologically, rainforests are characterized by a complex architecture and a uniquely humid, dark stable climate. They sustain many species that are incredibly specialized for the forest’s interior and understory conditions.

“Some species strongly avoid forest edges and are unable to traverse even narrow forest clearings,” Dr Goosem said. “Other tropical species are susceptible to hunting, increased predation, invasive species and being killed by vehicles.”

She said that limiting the width of roads, reducing vehicle speeds and maintaining a continuous forest canopy above roads were ways to reduce the impact on tropical rainforests.

“Bridges over watercourses that include a corridor of unflooded vegetation and natural streambed are especially effective for maintaining connectivity, both for terrestrial and aquatic fauna,” Dr Goosem said.

“Culverts and underpasses can provide effective avenues for movements of many animals, and can be designed to enhance their attractiveness to wildlife and efficacy in reducing road kill.”

However, not building roads in the first place was the best option, the scientists suggest.

“Actively limiting frontier roads is by far the most realistic, cost-effective approach to promote the conservation of tropical nature and its crucial ecosystem services,” said Professor Laurance. “As Pandora quickly learned, it is far harder to thrust the evils of the world back into the box than to simply keep it closed in the first place.”

Tropical rainforests mainly occur in developing nations, many of which are experiencing continued population growth, rapid economic development and intense natural resource exploitation.

“In many of these areas, industrial logging, oil and gas development large-scale agriculture and mining provide an economic impetus for the expansion of road and infrastructure developments, Professor Laurance said.

“The roads and paved highways that this creates play a key role in opening forested regions to exploitation from hunters and miners—exacerbated by often weak enforcement of environmental laws in remote frontier areas.

“New logging roads make forests greatly more accessible to exploitation by hunters, miners and settlers and disease and invasive species generally follow the influx of humans.”

In their paper, the scientists said that easy access for people was not the only effect roads and linear clearings have on tropical rainforests. These areas often act as barriers, greatly affecting water drainage, erosion and fire-maintained tropical woodlands.

Dr Susan Laurance said that animals too see roads as barriers.

“A striking feature of tropical forests is the high proportion of species that tend to avoid even narrow clearings or forest edges. Many species - such as those that are completely arboreal, adapted to flying in dense forests, or depend on specialized food resources - are halted by linear clearings,” she said.

There are those species, however, that do not avoid roads or other such clearings, resulting in what the scientists call “road-related mortality.”

The most obvious form is often vehicle road kill. Anteaters with poor eyesight, slow-moving sloths, and the Australian echidna—whose reaction is to freeze in the path of oncoming vehicles—are some of the many rainforest species that are particularly vulnerable to being struck by a vehicle.

The scientists also found levels of chemical and nutrient pollution to be elevated in areas where roads have been built. Effects of chemical pollution and nutrient runoff are especially serious for streams and wetlands near roads.

The mitigation research in Australia’s wet tropics undertaken by Dr Goosem and Professor Steve Turton has been funded by the Queensland Department of Transport and Main Roads, the former Rainforest CRC and more recently by the Australian Government's Marine and Tropical Sciences Research Facility.