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Limber pine skeleton G. Anderson |
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Whitebark pine is a "keystone" species. Of the trees in Glacier National Park, perhaps none is more important to wildlife and the integrity of the subalpine zone (forests just below treeline). Historically, annual pilgrimages by grizzly and black bears, Clark's nutcrackers, red squirrels, and many other species of birds and mammals moved to the nut crops of Glacier's whitebarks in August and fed there until October, in some cases.
Whitebark seed cones are unusual because they never open without help, and the large, protein-rich seeds have no "wings" for wind transport, like many other pines. The closed cones are found on the tips of upswept branches.
Three types of animals are perfectly suited to harvesting (and in one case planting) whitebark seeds. Red squirrels cut whole cones from the branches and stock-pile them in large caches nearby. Enter grizzly bears (or sometimes black bears when the larger grizzlies aren't around), who raid the caches and gorge themselves during a critical time in their "hyperphagia" fat build-up before hibernation.
Clark's nutcrackers, relatives of the jays and crows, have likely evolved in close relationship with the whitebark pines. They have a bill which is the perfect shape and size to remove seeds from the closed cones. Their throat pouch stores holds about 100 seeds at a time (up to 150 in a large bird). Some of the seeds are eaten immediately, but others are distributed by the birds up to eight or more miles from the seed tree. Nutcrackers bury 3 or 4 seeds (average) about an inch deep, and then move to another caching area, repeating the process. One nutcracker can make about 9,500 caches of 35,000 seeds per year. (Some research has suggested 98,000 seeds at 30,600 sites!). Nutcrackers are so busy with seed caching that they often get dyed light burgundy by rubbing against so many whitebark cones.
The spatial memory of nutcrackers is impressive, because they return to the cache sites for winter food, remembering the exact locations by nearby landmarks such as stumps and rocks. Depending on the need for winter food and the snow cover (nutcrackers have often been observed digging to a cache in a foot of snow), they return to most of the sites (average 70%, according to some research) and survive the winter and spring on stored food.
What happens to that other 30% of the seeds is the key. Most of the seeds are "planted" an inch deep on steep south slope openings or fresh burned areas, near treeline -- perfect places for whitebark pine seed germination. The seeds typically spend two winters dormant, perhaps waiting for the right moisture conditions and germinate into whitebark seedlings. The trees often grow in clumps of three or four, landmarks to the caching habits of nutcrackers.
The pines aren't just food for many. They also stabilize soil at treeline, places often subject to erosion problems, and provide shade and cover to many other plants and animals. They retain snowpack in their broad crowns, benefitting the hydrologic system, and provide sheltered conditions for other tree species to germinate which are not so tolerant of the open, windy conditions that they are. The whitebark ecosystem is an almost magical set of relationships, with the pine as the keystone to all of them.
Dendrologists (tree scientists) can piece together over a thousand years of climate and fire history in the tree-rings of ancient whitebarks. Glacial geologists find frozen whitebark pine trunks in glaciers and piece together paleo-climate back thousands of years more.
However, the future of whitebark pine ecosystems is seriously threatened. In 1910, a fungal disease of 5-needled pines, including the whitebark, was accidentally introduced in Vancouver, BC. It is called white pine blister rust. The results of that introduction have been devastating for 5-needle pines across the northwest and beyond, including whitebark pines in Glacier. Already, nearly half of Glacier's whitebark pines are dead, and more than 75% of the still-surviving trees are infected. Limber pines on the park's east side have also been hit hard.
Because of nearly a century of fire exclusion in the high elevations of the park, shade-tolerant subalpine firs have encroached on the whitebarks, who need burned areas for seeding and sunny places to grow. Fire exclusion has probably contributed to larger outbreaks of the mountain pine beetle, another deadly agent in the whitebark pine's world.
The blister rust has an alternate host in its life cycle, the genus Ribes, wild gooseberries and currants. For years, controlling Ribes was thought to be the way to control the rust and prevent infection of pines, so 2 million plants were removed and 15,000 gallons of 2,4,5-T herbicide were sprayed in Glacier. These expensive efforts proved nearly useless (aside from the number of people employed through the project). Some scientists think that Ribes thrives on disturbed soil, so the efforts perhaps helped the spread of blister rust. It is a bleak picture, and the hope for whitebark pines has come down to this: find rust-resistant trees, increase suitable habitat, partly through allowing natural ignitions to burn at high elevations, and do whatever we can to help the resistant seeds find places to grow. Normally, letting nature take its course is the byword in the National Park System, but because the rust is exotic, and the whitebark so important to a whole system, we may be involved for generations in their restoration. We have to prepare for a long, slow haul. Whitebark pines we plant today will be producing their first seeds at least 60 years from now.
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