Cutting up forests into ever-smaller bits starts a die-off of species that lasts decades -- an "extinction debt" incurred today and paid by future generations, says a study on forest fragmentation.
"It's our grandchildren and maybe more," said McGill University's Andrew Gonzalez, one of the co-authors of a paper published Friday in the journal Science. "It's several generations of human beings down the line."
Biologist Gonzalez and his colleagues have published what they say is the first study that measures the extent to which development has invaded forests around the world and estimates its long-term impacts.
They found more than 70 per cent of global forests are within a kilometre of a road, field, town or other human disturbance -- easily close enough to degrade forest habitat.
Specific information on Canada's rate of disturbance wasn't available. But previous studies found the eastern slopes of the Alberta Rockies have lost 6.8 per cent of their unprotected forests since 2000 and the oilsands region lost 5.5 per cent -- higher deforestation rates than in the Brazilian rain forest.
The global numbers are significant, said Gonzalez.
"These are frightening numbers. We had no idea."
The study compared results from seven long-term experiments on the impacts of fragmentation from Borneo to Canada.
"No matter what kind of forest you do that in, these experiments consistently show loss of biodiversity and wholesale changes to the functioning of these ecosystems."
Even when disturbance stopped, species loss didn't. Plants and animals kept disappearing as a freshly fragmented forest slowly stabilized -- a phenomenon first suggested by mathematical models in the '90s and referred to as "extinction debt."
"You incur a cost on the landscape and the final debt in terms of extinction is paid over time," Gonzalez said.
"It does compound. We get these long-term, long-lasting losses in biodiversity."
Some studies have shown it takes more than a century before a disturbed forest achieves stability.
Gonzalez noted that fragmentation effects are taking place at the same time forests are stressed by climate change. And Canada's boreal forest is experiencing some of the fastest climate change in the world.
"When you get climate change and forest fragmentation at the same time, that's quite a lethal cocktail."
Gonzalez and his colleagues want governments to do more to ensure that patches of forest remain connected through, for example, undisturbed corridors between them. France has laws stipulating that such pathways must be left.
A coalition of environmental groups has been urging the federal government to ensure at least 50 per cent of Canada's boreal forest remain protected. The region offers nesting habitat for billions of birds, some of which migrate as far south as Argentina.
Gonzalez said maintaining biodiversity and blunting the effects of climate change must be done in tandem.
"We can't treat these issues in a one-at-a-time way," he said. "In a global vision of what we can do for Canadian biodiversity, you have to address the climate problem and land use change together.
"Planting trees and reconnecting landscapes can not only improve our ability to store carbon, but also to maintain the connectivity that our biodiversity needs."
