Whitebark pine

Almost every whitebark pine standing at Glacier’s treeline started as a seed a bird buried and then failed to find again.

That is not a nice way of putting it. It is the mechanism. NPS calls whitebark pine an obligate mutualist of Clark’s nutcracker, because its seedlings sprout almost exclusively from Clark’s nutcracker seed caches. Run the deal in order. In late summer the tree carries purple cones packed with seeds that are 30 to 50 percent fat. A nutcracker pries them out with a long straight bill, loads dozens into a pouch under its tongue, flies off across the mountainside, and buries them a few at a time in shallow holes. Through the winter it digs up a remarkable number of them, months later, under snow. It does not dig up all of them. The ones it loses are the next forest.

So the tree gets planted and the bird gets fed, and neither one kept a backup plan. That is what “obligate” means here.

The seeds feed more than the bird. Grizzly and black bears go after whitebark nuts hard in late summer, stacking on fat before hibernation, and NPS notes the seeds matter most to females. Red squirrels raid the cones. Crossbills and blue grouse work the stands. One tree species is running the late-summer buffet up at timberline, which is why NPS calls it a keystone species: something that increases the biodiversity of a whole community.

It runs the water, too. The crown of a whitebark is broad and windswept, so it catches snow in winter and then shades that snow when the weather warms. The pile melts out slowly instead of all at once. Slower melt means less flooding in spring and creeks still running in August.

Now the hard part. Four things are killing this tree at the same time. White pine blister rust is a fungus that arrived from another continent and is the main driver. Mountain pine beetles build up in lodgepole stands lower down and then climb into the whitebark. A century of putting out every fire let subalpine fir and Engelmann spruce grow up and crowd whitebark off its own ground. And warming is shrinking the strip of mountain cold enough for it. In Glacier, a 1996 study put mortality at 44 percent, with about 78 percent of the trees still alive already infected. In December 2022 the U.S. Fish and Wildlife Service listed whitebark pine as a threatened species under the Endangered Species Act.

Find one and check it yourself. Above 6,000 feet, so anywhere around Logan Pass. Pull a needle bundle and count: five needles means whitebark. Look for pale gray bark, and on the ground that takes the most wind look for a tree growing sideways and knee-high instead of up, a shape called krummholz. Then watch the branches for a gray bird with black-and-white wings. If it is working a cone, you are looking at the only reason the tree is there.