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Life Zones of The Rocky Mountains

The Rockies are a challenging, difficult landscape. In order to survive, plants and animals must find a way to exploit some environmental niche in a unique way. Plants need a specific mixture of soil quality, nutrients, moisture, sun-exposure and temperature. Wildlife looks for food, shelter, protection, and numerous other less obvious characteristics of range. As we examine the plants and animals of the Rockies, we notice these preferences in the regular appearance of certain individuals within specific environments. For instance, while the lodgepole pine defines the valley bottoms, the alpine larch is able to take advantage of upland habitats abandoned by most of its neighbours. When we look at wildlife, we notice that mountain goats prefer the rocky world of the alpine while the elk wander the valleys. While these may be obvious examples, an understanding of mountain habitats can help us to better understand the many plants and animals found in the mountains.

For simplicity, the mountain environment is usually divided into three main life zones: the Montane, Subalpine and Alpine. Each provides unique conditions that enable those species with the ability to take advantage of their special mixture of climate, landscape and plantlife to thrive.

Lower Foothills

The Lower Foothills represents an area of transition between the Aspen Grovelands of the plains and the lodgepole pine dominated Upper Foothills. The landscape is usually rolling with sandstone ridges in the foothills and shale valleys. Glacial deposits dominate, but there may be extensive organic material in low lying area’s. It has a mild winter climate as regular Chinook winds help keep the mercury from dropping.

Look for a mixture of white spruce, lodgepole pine, trembling aspen and balsam poplar. In more northern sites, black spruce and tamarack may be present. In the shadow of this mixed forest, is an equally diverse understory. Low-bush cranberry, buffaloberry, prickly rose, and green alder are common forest residents, while wild sarsaparilla, reed grass and hairy wild rye dominate the margin.

Upper Foothills

The Upper Foothills is marked by an almost uniform canopy of lodgepole pine. Occasionally aspen stands will survive on dry, sunny, south-facing slopes. White spruce occurs intermixed with lodgepole pine depending on the length of time since the most recent forest fires. Black spruce occurs in northern portions of the Upper Foothills. Beneath the trees, bilberries (blueberries), Labrador tea and green alder dominate.

As you rise above the lower foothills, the relationship between sandstone ridge and shale valley is maintained, but the moisture level increases to make this the wettest ecoregion on the eastern slopes with an average of 540 mm annually.

Montane

The Chinook blasted Bow Valley forms a classic example of the true Montane. Douglas-fir forms a dominant presence along with lodgepole pine, white spruce, limber pine and grasses. Limber pine is found on dry exposed ridges (along the trail to the Hoodoos in Banff Townsite). Look for buffaloberry, bearberry, snowberry and juniper as understory. The true Montane is connected to our mountain passes, and their adjacent eastern slope valleys. The Bow and North Saskatchewan valleys are excellent examples. This is one of our warmest ecoregions with strong Chinook winds and regular snow-free periods in winter.  

Subalpine

As the white spruce and lodgepole pine begin to give way to Engelmann spruce and subalpine fir, so begins the Subalpine. This transition occurs at an average elevation of 1,675 m (5,494 ft), varying with latitude, elevation, sun exposure, and a plethora of more subtle factors. As you climb in elevation, the forest cover opens up, and the size of the trees diminish. At the upper extend of the Subalpine, the trees take on a low, shrub-like, twisted appearance (kruppelholz), before they finally disappear at the entrance to the Alpine. Beneath the trees, grouseberry, and false-huckleberry slowly give way to moist heather and willow communities.

This is a rugged landscape with a mixture of glacial deposits and bedrock exposures. With an excess of 200 cm of snowfall annually, it receives more snowfall than any other eastern slope ecoregion.

Alpine

There is rarely any question as to the end of the Subalpine and the start of the Alpine. Suddenly the last twisted kruppelholz gives way to an open landscape of heather, willows, and sturdy wildflowers. This is an extremely diverse Ecoregion, despite its desolate appearance. For instance, within the Alpine of Kananaskis Country, almost 400 species of plants have been identified, compared to less than 350 in British Columbia’s coastal alpine. The vast majority of plants are either prostate shrubs (like heathers) or perennials. Few annuals or bulb forming flowers are able to survive the very short growing season of the alpine. Most biologists agree that the Alpine begins at the point at which the average temperature for the warmest month of the year is 10°C (50°F). In the Canadian Rockies, this drops from an average of 2,450 m (8,038 ft) at Highwood Junction in the south Kananaskis, to 2,200 m (7,218 ft) in Jasper National Park.

The Western Slopes

Crossing the continental divide, the landscape may not suddenly seem different, but the vegetation changes almost instantly. The western slopes receive much higher amounts of moisture than the drier eastern slopes. This is reflected in forests of western red cedar and western hemlock along with the occasional Douglas-fir and lodgepole pine forest in drier locales. Within minutes of crossing the divide, plants appear that are not found on the opposite side of the mountains. Plants like thimbleberry and Douglas maple are rare on the eastern slopes, while cedar and hemlock are completely absent.


All Material © Ward Cameron 2005