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Introduction
Whitebark Pine is an evergreen, coniferous tree species of western North America, where it is found seven US states (CA, ID, MT, NV, OR, WA, WY) and two Canadian provinces (AB, BC). In British Columbia, it is frequent in southern BC east of Coast-Cascade Mountains and is rare northward to central and northeastern BC. It is found on mesic to dry slopes in the subalpine to alpine zones, and is considered a keystone species. Whitebark pine is in the white pine group, with 5 bluish, stiff needles per bundle that are clustered towards the ends of the branches. Bark is smooth and chalky-white on younger trees. This species has a variable shape and may be a small dwarfed tree or shrubby and sprawling (Douglas et al. 1998). Freshly cut wood is sweet scented.
Whitebark pine is an important food source for many birds and small mammals, and particularly for Clark's Nutcracker, which plays an important role in seed dispersal in this species. Clark's Nutcrackers cache seeds in the soil and use the caches when food is limited. Cache sites are usually good for seed germination, and can result in a clumped distribution of this species. Whitebark pine is threatened by White Pine Blister Rust, which was introduced from Europe, and which causes significant die-off. It is also threatened by Mountain Pine Beetle in western North America.
General: Often contorted and dwarfed, 5-10 m tall, or a shrubby sprawling timberline tree, but also straight and up to 20 m; bark thin with light-whitish scales; young twigs hairy.
Leaves: Needles in bunches of five, clustered towards ends of branches, (3) 4-7 cm long; yellow green.
Cones: Seed cones egg-shaped, deep red to purple, (3.5) 5-8 cm long; scales remain closed and shed the seeds slowly, rarely falling from tree intact; pollen cones red.
2. Needles in bundles of 3, 12-20 cm long..........................Pinus ponderosa
2. Needles generally in bundles of 2, 2-6 cm long.
3. Cones spreading at right angles or reflexed, the scales armed with prickles...............................Pinus controta (2 varieties)
3. Cones directed towards the apex of the shoot, strongly incurved or divergent, the scales unarmed or armed with minute prickles..................Pinus banksiana
1. Needles usually 5 in a bundle.
4. Cones long-stalked, 15-25 cm long, 6-9 cm thick at maturity; cone scales thin and flexible; seeds prominently winged..........................Pinus monticola 4. Cones sessile or subsessile, 5-25 cm long, cone scales thick, woody, and sometimes remaining closed, seeds wingless or wings short and remaining attached to scale.
5. Cones 8-25 cm long, opening at maturity; scales light brown, thinned somewhat toward the tip...............................Pinus flexilis
5. Cones 5-8 cm long, remaining closed and tardily shedding the seeds at maturity; scales purplish, becoming thickened rather than thinnish toward the tip....................................Pinus albicaulis
Source: The Illustrated Flora of British Columbia
Habitat / Range
Mesic to dry slopes in the subalpine to alpine zones; frequent in S BC in and E of Coast-Cascade Mountains, rare northward to C and NE BC; E to SW AB and S to CA, NV and WY.
Whitebark pine belongs to the pine family, subsection Cembra (the stone pines), which are typified by their large, wingless seeds. These large seeds provide a food source for bears prior to hibernation through excavation of red squirrel caches. Whitebark pine is also tied to the ecology of Clark's Nutcracker in BC: "Whitebark pine, like other stone pines, has co-evolved with nutcrackers. The nutcrackers rely on stone pine seeds as their principal food source "for at least 9 months of the year and for raising the young. In addition to special adaptations on gathering, transporting, caching, and finding again the hoarded seeds, the whole annual cycle of the nutcracker's life (time of breeding and moulting), its mating system, and its habitat use are adjusted to the use of pine seeds" (Tomback et al. 1990)." (The Gymnosperm Database 2011).
Similar Species
Whitebark pine has 5 needles per bundle, which separates it from lodgepole pine and ponderosa pine. However it is similar to limber pine and white pine, which also have 5 needles per bundle. Limber pine and whitebark pine are separated based on seeds and pollen cones. "In whitebark pine, the cones are 4-7 cm long, dark purple when immature, and do not open on drying, but the scales easily break when they are removed by Clark's Nutcracker to harvest the seeds. In limber pine, the cones are 6-12 cm long, green when immature, and open to release the seeds; the scales are not fragile. Whitebark pines almost rarely has intact old cones lying under them, whereas limber pines usually do. The pollen cones of whitebark pine are scarlet, and yellow in limber pine." (Wikipedia 2011). Needles can separate whitebark pine and white pine: "whitebark pine needles are entire (smooth when rubbed gently in either direction), whereas western white pine needles are finely serrated (feeling rough when rubbed gently from tip to base). Whitebark pine needles are also usually shorter, 4-7 cm long, to Western White Pine's 5-10 cm (though note the overlap)." (Wikipedia 2011)
Ecology
Ecological Framework for Pinus albicaulis
The table below shows the species-specific information calculated from original data (BEC database) provided by the BC Ministry of Forests and Range. (Updated August, 2013)
A shade-intolerant, subalpine, Western North American evergreen conifer distributed more in the Pacific than the Cordilleran region. Occurs in continental alpine tundra and subalpine boreal climates on moderately dry to fresh, nitrogen-medium soils; its occurrence increases with increasing continentality and decreases with increasing latitude. Common in parkland forests on water-shedding sites which are free of snow early in the year. Often grows with Engelmann spruce and subalpine fir in the coast-interior ecotone. Characteristic of continental subalpine forests.
