Conservationists patch it up

Urban wildlife may not use green corridors.

Green corridors do little to aid wildlife, say UK ecologists. Their discovery that isolated wild ground contains just as many plant species as do patches linked by continuous greenery casts doubt on current conservation priorities.

“The proportion of organisms that use [wildlife corridors] is exceedingly small,” says botanist Mark Hill of the Centre for Ecology and Hydrology in Monks Wood. Only vertebrates seem to benefit, he says.

“Resources would be much better spent managing habitat in the right way, rather than worrying about connections between patches,” adds conservation biologist Andrew Pullin, of the University of Birmingham.

Many environmental management plans, including the European Union’s Habitat’s Directive, promote wildlife corridors, such as hedges, railway embankments and canals. The assumption is that they help species to travel around the landscape, opening up habitat and reducing the risk of extinction.

“All other things being equal, they’re good, but all other things aren’t equal,” says Dave Dawson, biodiversity strategy manager with the Greater London Authority (GLA) and an expert on wildlife corridors.

The GLA’s conservation policy values corridors, but makes them a low priority. Enhancing or defending habitat is usually cheaper and more worthwhile, says Dawson. “If you’ve got limited resources, creating a corridor is the last thing you should put them into.”

Cross purposes

In 1998, the UK Natural Environment Research Council commissioned researchers, including Hill and Pullin, to look into the influence of corridors on wildlife in and around the city of Birmingham.

Early results suggest that many plants easily cross inhospitable territory, Hill told this week’s British Ecological Society’s Winter Meeting in Warwick, UK.

Open spaces on or near corridors have no more plant species than do more isolated counterparts, the researchers found. Most seeds are moved by building projects, cars and people. Birds and the wind are also important.

Green routes through the city can be habitat in their own right, and they can help to bring people into contact with wildlife, says Hill. “But they’re not a way that plants get about.”

Pullin, meanwhile, is comparing the DNA of butterflies from isolated and interconnected patches. Preliminary results suggest that butterflies can get to the two types of habitat with equal ease. “We frequently underestimate the dispersal capabilities of a lot of species,” he says.

Corridors of power

But ecologists may be reluctant to abandon corridors. They might benefit species other than those examined in this study, warns Chris Parry, principal ecologist with conservation charity the Wildlife Trust for Birmingham and the Black Country. “It’s common sense that habitats are better linked than isolated,” he says.

Plants and animals don’t see links in the same way as we do, counters Pullin. “They don’t look at a map and think, ’this is the best way to get from A to B’.”

Corridors fail some of the species that might be thought to need them most, agrees Dawson. Newts, for example, like to migrate in straight lines from their winter homes to their breeding ponds.

“The species that theoretically most need them tend to have fussy habitat requirements,” Dawson says. “The whole landscape needs to be amenable to wildlife.”