Rocky Mountains Losing Whitebark Pine

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A fungus introduced from Europe is well on its way to rendering whitebark pine trees extinct in some North American national parks, scientists warn. A large proportion of whitebark pines in Canada's and Montana's Rocky Mountains are infested with or already dead from white pine blister rust.

As a keystone species, whitebark pine's absence will cause repercussions throughout the harsh mountain ecosystems it once thrived in. Its presence on exposed spots enables other plants to grow. The tree's ample seeds also nourish wildlife ranging from birds to grizzly bears.

Whitebark pine seed yields have already dwindled. Long before killing a tree, the blister rust can shut down seed production. It strangles the upper branches where the cones in this species are confined. The lack of whitebark pine trees less than 1.3 metres high in 14% of the areas surveyed indicates that seed supply is substantially curtailed.

Where seedlings do sprout, up to one-quarter are under attack from the rust. Once a young tree develops cankers, it usually succumbs within three years.

Throughout the mountains stretching from Glacier National Park in Montana to Jasper National Park in Alberta, blister rust has infested 57% of the thousands of whitebark pine trees examined by park scientists. Out of the 170 sites inspected, 98% harboured blister rust.

The numbers of dead and infested trees are rising. In Waterton Lakes National Park, where the extent of blister rust was tracked over seven years, infested trees increased by 3% a year. Blister rust had spread from 43% of the pine in 1996 to 71% by 2004. Over the same period, mortality had grown from 26 to 61% of whitebark pines.

The areas most intensively invaded by rust are in northern Montana and southern British Columbia and Alberta, where 73% of whitebark pines are infested. At the northern end of the species' range near McBride BC, infestation rates are also high, comprising 60% of trees. In between, about 16% of whitebark pines have rust in Yoho, Banff and Kootenay National Parks. The fungus concentrates in moister climates on the western flank of the Rockies, and where other plant species that host blister rust exist.

At the time of this field research in 2004, white pine blister rust had caused most of the whitebark pine mortality. But the demise of whitebark pine is being hastened by mountain pine beetle, whose populations have recently been expanding and spreading. The insect targets older pines, while the rust tends to take younger trees. With the two pests working in unison, both the time left and the options available for saving whitebark pines have diminished.

Reference

Cyndi M. Smith, Brendan Wilson, Salman Rasheed, Robert C. Walker, Tara Carolin and Brenda Shepherd. 2008. Whitebark pine and white pine blister rust in the Rocky Mountains of Canada and northern Montana. Canadian Journal of Forest Research. 38(5): 982-995. Journal Article

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