National parks may not protect vulnerable plants and animals in the future as climate change triggers a massive geographic reshuffle that ignores park boundaries.

The research by a U.S. team led by Catherine E. Burns from Yale University in Connecticut is published in today's issue of the Proceedings of the National Academy of Sciences.

"U.S. National Parks and bioreserves are key conservation tools used to protect species and their habitats within the confines of fixed political boundaries," write Burns and colleagues. "This ... may be their Achilles' heel as conservation tools in the face of emerging global-scale environmental problems such as climate change."

The researchers described climate changes, expected to occur in the coming century, as causing changes in species composition on a scale "unprecedented in recent geological time". The impact on vegetation would, in turn, impact on habitat and species distribution.

"First, several national parks are expected to face significant losses in current species diversity," report Burns and colleagues. "Second, all parks should experience a virtual tidal wave of species influxes as a direct consequence of vegetation shifts due to climate change."

The researchers gathered data on the distribution of vegetation and mammals living in eight U.S. national parks, including Yellowstone, Yosemite, and Shenandoah. They then constructed a model to predict how park vegetation, and consequently mammals living in particular vegetative habitats, might respond to a doubling of current atmospheric carbon dioxide and the associated rise in temperatures.

"A species was recorded as potentially present in a park, under the future climate scenario, if acceptable habitat for that species was predicted to occur within park boundaries after a doubling of carbon dioxide," they said. The researchers concede that this method is a rough "first-cut approximation" of what might actually happen and that they did not consider geographic barriers to dispersal.

The model suggests that while most mammal species in the U.S. are expected to be able to maintain their current ranges and expand them, others will lose out. Rodents, bats, carnivores and insectivores, for example, are all predicted to be able to range further than they do today. But red squirrels, the southern red-back vole and flying squirrels are among those thought to be most sensitive to climate change in many parks.

According to the model, parks stand to receive up to 92 % more mammal species through immigration and vegetation changes could force up to 20 % of current mammal species to relocate outside national parks. The scientists argue that such a major reshuffle would leave parks could transform ecosystem processes in "unforeseen ways". An influx of new species, for example, might increase competition for resources or cause fundamental and irreversible changes in the way some ecosystems function.

Fragmented national parks even more vulnerable
Professor Michael Archer, director of the Australian Museum in Sydney, told ABC Science Online that the results were probably broadly applicable to other nations: "Already there is evidence from around the world that hundreds of individual species in many different groups are moving house - at speeds of on average 6.1 kilometres a decade - in response to global warming," he said.

Recent studies had strongly suggested that many plant and animal species were changing their flowering, breeding or migration times as well: "Some botanists suggest that many trees planted today will be struggling to survive a century from now in what will have become environments that are unacceptable to them simply due to climate change."

However, Archer believes that the situation could be much worse than predicted by Burns and colleagues because in many cases around the world national parks are fragmented. This makes it almost impossible for many plant and animal communities to shift naturally in response changes in environmental conditions.

"Our national parks in Australia, for example, have effectively become ecological islands in a sea of farms and grazing lands, yet we know that real-life islands tend to be death-traps for mammals," he said. "The changes wrought by the greenhouse effect mean that plants and animal will need to change locality and Australia, for one, needs a conservation system that leaves open movement paths to any point of the compass."