Saturday, April 11, 2009
Tree fungus is bad news for Clark's Nutcracker
It turns out that when white pine blister rust hits whitebark pines in subalpine forests, it can not only destroy the trees, but make it impossible for future generations of whitebark pines to grow, by taking away a major food source for the Clark's nutcracker.
The Clark's nutcracker and the whitebark pine have what ecologists call a "mutualistic" relationship. Clark's nutcrackers eat whitebark pine seeds. When the cones form in late summer, the Clark's nutcrackers harvest them and bury them by the thousands. They have special pouches under their tongues for carrying seeds around.
When the nutcrackers breed, which can be as early as January, they dig up the seeds and feed them to their young. They're smart birds and remember where all their seeds are buried -- almost. The seeds that are forgotten are the only ones the whitebark pine makes that have a chance to germinate. The bird eats other things, but the tree doesn't have another way to disperse seeds.
Enter white pine blister rust, which strikes the cone-bearing branches of the tree first.
In a paper in the April issue of Ecological Applications, three researchers from the University of Montana report that in areas hit hard enough by the fungus, so that the number of cones fall below 1000 a hectare, the birds retreat and look for food elsewhere, so that those pines still producing seeds have no way to disperse them.
Photo from Montana Fish, Wildlife and Parks.