Botanists divide the Canadian Rockies into three distinct vegetation zones (also called biomes): montane, subalpine, and alpine. The boundaries of these zones are determined by several factors, the most important being altitude. Latitude and exposure are also factors, but less so. Typically, within any 1,500 meters (4,920 feet) of elevation change, you’ll pass through each of the three zones. These changes can be seen occurring most abruptly in Waterton Lakes National Park. Conifers (evergreens) predominate in the montane and subalpine, whereas above the tree line, in the alpine, only low-growing hardy species survive.
The foothills, along with most major valleys below an elevation of about 1,500 meters (4,920 feet), are primarily cloaked in montane forest. Aspen, balsam poplar, and white spruce thrive here. Lodgepole pine is the first species to emerge after fire. Its hard seed cones are sealed by a resin that is melted only at high temperatures. When fire races through the forest, the resin melts and the cones release their seeds. The lodgepole is named for its straight, slender trunk, which natives used as a center pole for tepees.
On dry, south-facing slopes, Douglas fir is the climax species. Where sunlight penetrates the forest, such as along riverbanks, flowers like lady’s slipper, Indian paintbrush, and saxifrage are common. Large tracts of fescue grassland are common at lower elevations. The montane forest holds the greatest diversity of life of any vegetation zone and is prime winter habitat for larger mammals. But this is the habitat where most development occurs and therefore is often much changed from its natural state.
Subalpine forests occur where temperatures are lower and precipitation higher than in the montane. In the Canadian Rockies, this is generally 1,500–2,200 meters (4,920–7,220 feet) above sea level. The upper limit of the subalpine zone is the tree line. Approximately half the flora of the mountains falls within this zone. The climax species are Engelmann spruce and subalpine fir (recognized by its spirelike crown), although extensive forests of lodgepole pine occur in areas that have been scorched by fire in the last 100 years.
Before lodgepole pines take root in fire-ravished areas, fireweed blankets the scorched earth. At higher elevations, stands of larch are seen. Larches are deciduous conifers—unlike those of other evergreens, their needles turn a burnt orange color each fall, producing a magnificent display for photographers.
The alpine zone extends from the tree line to mountain summits. The upper limit of tree growth in the Canadian Rockies varies between 1,800–2,400 meters (5,900–7,900 feet) above sea level, dropping progressively to the north until it meets the treeless tundra of the Arctic. Vegetation at these high altitudes occurs only where soil has been deposited. Large areas of alpine meadows burst with color for a short period each summer as lupines, mountain avens, alpine forget-me-nots, avalanche lily, moss campion, and a variety of heathers bloom.
© Andrew Hempstead, from Moon Western Canada, 3rd Edition