Alpine Larch

Alpine Larch Pinaceae Pine family Stephen F. Arno Alpine larch (Lurix lyallii), also called subalpine larch and Lyall larch, is a deciduous conifer. Its common name recognizes that this species oRen grows higher up on cool exposures than any other trees, thereby occupying what would otherwise be an alpine tundra. Both early-day botanical explorers and modern visitors to the high mountains have noted this tree’s remarkable ability to form pure groves above the limits of evergreen conifers. Alpine larch inhabits remote high-mountain terrain and its wood has essentially no commercial value; however this tree is ecologically interesting and esthetically at- tractive. Growing in a very cold, snowy, and often windy environment, alpine larch usually remains small and stunted, but in windsheltered basins it sometimes attains large size-maximum 201 cm (79 in) in d.b.h. and 29 m (95 ft) in height. This species is distinguished from its lower elevation relative western larch (Larix occidentalis) by the woolly hairs that cover its buds and recent twigs, and frequently by its broad, irregular crown. Habitat Figure l-The native range of alpine larch. Native Range amounts atop numerous other ranges and peaks in western Montana and northern Idaho (4). In British Alpine larch (fig. 1) occupies a remote and rigorous Columbia and Alberta, alpine larch is common along environment, growing in and near the timberline on the Continental Divide and adjacent ranges, and in high mountains of the inland Pacific Northwest. Al- the Purcell and southern Selkirk Ranges. though alpine larch is found in both the Rocky Moun- In the Cascade Range alpine larch is found prin- tains and the Cascades, the two distributions are cipally east of the Cascade Divide and extends from separated at their closest points by 200 km (125 mi) the Wenatchee Mountains (47” 25’ N.) in central in southern British Columbia. This and smaller gaps Washington northward to about 21 km (13 mi) inside in the species’ distribution generally coincide with an British Columbia (49” 12’ N.). Within this limited absence of suitable high mountain habitat. distribution covering a north-south distance of only In the Rocky Mountains alpine larch extends from 193 km (120 mi), alpine larch is locally abundant in the Salmon River Mountains of central Idaho, the Wenatchee, Chelan, and Okanogan ranges. latitude 45” 28’ N. northward to latitude 51” 36’ N. several kilometers past Lake Louise in Banff Nation- al Park, AB. [A fossil larch, probably of this species, Climate grew between 1000 and 1250 A.D. near the Athabas- ca Glacier (Columbia Icefield) 90 km (56 mi) Alpine larch grows in a very cold, snowy, and northwest of today’s northernmost known isolated generally moist climate. The following description is alpine larch tree (18).] Within this distribution, al- based on weather records from several sites in and pine larch is common in the highest areas of the near alpine larch stands (2). For more than half of Bitterroot, Anaconda-Pintler, Whitefish, and Cabinet the year, mean temperatures are below freezing. The Ranges of western Montana. It is also found in lesser cool “growing season,” as defined by mean temperatures of more than 6” C (42” F) (6), lasts about 90 days, and occasional frosts and snowfalls occur The author is Research Forester, Intermountain Research Station, during the summer. July mean temperatures range Ogden, UT. from about 9” to 14” C (48” to 58” F). Long-term 152 Larix lyallii record low temperatures for late June through mid- less than 12,000 years. Chemical weathering is August are near -5” C (23” F), whereas correspond- retarded by the short, cool summer season. Also, ing record highs are near 27” C (80” F). January nitrogen-fixing and other microbiotic activity that mean temperatures range from about -14” C (7” F) might enrich the soil is apparently restricted by low in Alberta to -7” C (20” F) in the northern Cascades. soil temperatures and high acidity. Long-term record low temperatures have undoubted- Throughout its distribution, alpine larch commonly ly reached -50” C (-58” F) in some stands near the grows on slopes covered with granite or quartzite Continental Divide in Alberta and Montana. talus (boulders), which have not been previously oc- Mean annual precipitation for most alpine larch cupied by vascular plants. The species also grows in sites is between 800 and 1900 mm (32 and 75 in), cracks in massive bedrock. These undeveloped soils the larger amount being more prevalent near the would probably be classified (31) as fragmental and crest of the Cascades. Most stands in the Montana as loamy skeletal families within the order Entisols Bitterroot Range evidently receive 1000 to 1500 mm (Cryorthents). Such substrates have been referred to (40 to 60 in). About 75 percent of this precipitation as azonal soils, and more specifically as Lithosols in is snow and sleet. earlier classifications. Typically, the new snowpack begins to accumulate On sites that have appreciable soil development or by late October. By mid-April, it reaches a maximum fine material (including recent moraines), the soils depth averaging about 2.1 m (7 ft) in stands near the are still rocky and immature. These would be clas- Continental Divide and 3.0 to 3.5 m (10 to 11 R) sified as Inceptisols-usually Typic Cryochrepts (17). farther west. Maximum water content of the snow- On some sheltered slopes, deposits of volcanic ash pack is attained in May and reaches about 75 cm (30 in soil profiles are sufficiently thick to require recog- in) in stands near the Continental Divide and 100 to nition as Andic Cryochrepts, in a medial over loamy 125 cm (40 to 50 in) farther west. The snowpack does skeletal family (15). Some of the best-developed ash- not melt away in most stands until early July. layered soils beneath alpine larch stands are Typic Average annual snowfall is probably about 1000 cm Cryandepts, which nearly fit the description of zonal (400 in) in most stands west of the Continental Brown Podzolic soils in high elevation forests given Divide. Small amounts of stunted alpine larch grow by Nimlos (19). These soils are strongly acidic and on wind-exposed ridgetops and other microsites have a distinct, well-developed cambic B horizon. where snow accumulation is much less than the Throughout the range of alpine larch, pH values averages indicated above. were found to be very acidic, ranging from 3.9 to 5.7 The inland Pacific Northwest often has a droughty in the mineral soil (B horizon) (2). Bitterroot Range period for a few weeks in late summer. This drought sites had an average pH of 4.6. Such strongly acid, effect is minor in most alpine larch sites; however, shallow, rocky, and cold soils are extremely infertile. dry surface soils may prevent seedling establishment Alpine larch grows on several types of geologic in certain years. A modest quantity of rain falls substrates but has an affinity for acidic rock types, through July and August, averaging 25 to 50 mm (1 being most abundant on granitic and quartzite sub- to 2 in) per month in the United States, much of it strates and absent or scarce on nearby limestone or associated with thunderstorms. In the Canadian dolomite (4,Zl). This distribution contrasts markedly Rockies summer precipitation is greater, 50 to 90 mm with that of several other cold-climate conifers, in- (2.0 to 3.5 in) per month, and more of it comes in cluding Siberian larch (L. sibirica) and tamarack (L. Pacific frontal systems. Summertime relative Zaricind, which often grow on basic, calcium-rich humidity in alpine larch stands remains consistently sites (16,23). higher than that recorded at lower elevations. Most alpine larch stands annually experience Alpine larch achieves its best growth in high cirque winds reaching hurricane velocity, 117 km/h (73 basins and near the base of talus slopes where the mi/h) or more, during thunderstorms or during the soils are kept moist throughout the summer by passage of frontal systems. Ridgetop stands are ex- aerated seep water (fig. 2). It can also tolerate boggy posed to violent winds most frequently, wet-meadow sites having very acidic organic soils. The species is most abundant on cool, north-facing slopes and high basins where it forms the uppermost Soils and Topography band of forest (fig. 3). It also covers broad ridgetops and grows locally under relatively moist soil condi- Although soil development in alpine larch stands tions on south-facing slopes. In the Canadian Rock- varies, most soils are immature. Generally alpine ies, where summer rainfall is more abundant, it is larch sites have undergone intense alpine glaciation often found on south slopes. The extreme lower and during the Pleistocene and have been deglaciated for upper altitudinal limits of subalpine larch, over its 153 Larix lyallii Figure 3-Alpine larch on a snowy, rocky site at the base of a northfacing cliff: m (6,500 and 7,800 R) and in the northern Cascades, Figure S-Alpine larch on talus in a high basin, 2530 m (8,300 ftj between 1830 and 2290 m (6,000 and 7,500 ft). elevation, on Lo10 Peak, near Missoula, MT. Associated Forest Cover entire geographic range, are apparently 1520 and 3020 m (5,000 and 9,900 ft). The lowermost in- dividuals are found in shady cirques and canyons in Alpine larch grows in pure stands and also in as- the North Cascades, while the highest limits apply sociation with whitebark pine (Pinus albicaulis), sub- to scattered stunted trees on Trapper Peak in the alpine fir (Abies Zusiocurpu), and Engelmann spruce Montana Bitterroot Range (2).

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