Ecology of Alpine Larch (Larix lyallii Parl.) in the Pacific Northwest

Abstract

Alpine larch (Larix lyallii) grows in or near the timberline zone on high mountains of the inland northern portion of the Pacific Northwest. Unlike other subalpine conifers, which are evergreens, this deciduous larch displays an affinity for cold rocky sites and often grows in tree form higher up on north slopes than even krummholz (shrubby) forms of its associates. Overstory and understory vegetations in alpine larch communities were only indirectly correlated. Vaccinium scoparium, Luzula glabrata, and Phyllodoce empetriformis were the most common understory dominants. The distinctly snowy—cold—timberline nature of alpine larch habitats is emphasized by the presence of Cassiope mertensiana, Phyllodoce glanduliflora, and Abies lasiocarpa krummholz among the 11 most common understory species. Unlike the larch, which is generally restricted to the timberline zone, nearly all associated plants have broader distributions in the subalpine forest proper or above tree limit. Alpine larch is a climax species on a wide variety of sites too severe for the more shade tolerant evergreens to form unbroken stands because of shortness of growing season, rock terrain, avalanches, blizzards, or extreme dryness or bogginess. When alpine larch ascends into what would otherwise be a strictly alpine habitat (above the limits of other conifers), its stands apparently modify the surface environment since subalpine understory species are generally able to ascend with it. Rarely the undergrowth is dominated by tundra species. Alpine larch is superior in invading freshly glaciated sites. The positive correlation of alpine larch to acidic substrates poor in mineral ions is in contrast to the substrate relationship of many other timberline conifers, which are calciphiles.

Appendix 1: Assessment tools

“…Alaska yellowcedar (Chamaecyparis nootkatensis), Pacific silver fir (A. amabilis), and mountain hemlock (Tsuga mertensiana) are most common in the Olympics and Cascades. Whitebark pine (P. albicaulis) is found primarily in the eastern 11,49,75,105,112,114,115,139,144,221 . Natural Disturbance Regime.…”

Fire ecology of the forest habitat types of northern Idaho

“…The species often grows in small groves and pioneers on rockslides and talus where moisture is available (Arno and Habeck 1972). In the lower portion of its elevational distribution, alpine larch occurs with subalpine fir, Engelmann spruce, and whitebark pine.…”

“…Mature alpine larches have high, open crowns but relatively thin bark; they are protected from fire more by their habitat than by physiological characteristics. Northern Idaho's severe Sundance Fire of 1967 killed most of the whitebark pine on ridgetops and much of the spruce and fir in cirques, but caused only minor damage to the isolated stands of alpine larch (Arno 1970).…”

“…On most sites, competitors do not grow well enough to overtop alpine larch. At relatively low elevations, however, where subalpine fir and Engelmann spruce can thrive, fire enables alpine larch to remain a major forest component (Arno 1970).…”

“…Alpine larch has a very limited distribution in northern Idaho. It can pioneer on rockslides and talus, and also occurs on moist, high-elevation sites where winter desiccation causes high mortality in other conifers Arno and Habeck 1972). In northern Idaho, alpine larch stands occur in the Bitterroot Mountains and in the Kaniksu National Forest.…”