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