Valley bottoms and mountain peaks
Much of the diversity in the Rockies is driven by the influence of elevation. Ecosystems in the Rocky Mountains are typically grouped into three main categories
A montane white spruce forest
Montane ecosystems are found in the lower elevation areas of the Rockies, such as valley bottoms, and the foothills on the eastern edge of the mountains. These systems are characterized by a longer growing season, more moisture, and high amounts of tree cover. Rivers and large creeks often flow through the valley bottoms, or lakes can form, providing crucial movement corridors for fish and land animals. You can also find wetlands in flatter areas, home to migratory birds, beavers, and moose.
The Montane
A subalpine meadow with Western Larch and Subalpine Fir
The Subalpine
This ecosystem is a transition zone between the montane ecosystems of the valleys and foothills and the alpine ecosystems found near peaks and along ridge-lines. Generally they are found at elevations between 1400 and 2100m above sea level. These ecosystems are often much drier than montane ecosystems, and usually support much lower levels of tree cover. Instead of trees, you can often find grasses, shrubs, and lichen growing in thin soils. These plant communities are better adapted to the low moisture and high-wind environments present in the exposed sub-alpine.
The small wildflowers typically present in an alpine meadow
The Alpine
Alpine ecosystems are like islands in the sky. These environments occur at the upper edges of where plant life can exist. Alpine ecosystems are often complex landscapes of bare rock, small ponds or streams, and open meadows or grasslands. Plants find and exploit small pockets of sheltered terrain that have more moisture and warmer temperatures than the rest of the alpine. With a unique climate compared to lower elevation areas, these ecosystems are home to species that can handle long winters under the snowpack, and cool windy summers. The species that can survive in such environments are often so well adapted to alpine systems that they are unable to survive in the lower elevation valleys in the mountains. This means that each alpine patch is functionally isolated from other alpine ecosystems. This isolation makes these systems more at risk of extinction. In valleys, if a species disappears from an area, individuals of that species can immigrate from neighbouring areas to replace the loss. With neighbouring areas being rare in the alpine, once a species is lost, it is unlikely that we will see re-introductions from dispersing neighbours.
How are these ecosystems changing?
There are many different processes acting simultaneously to drive change in the Rockies, but in general they can be grouped into three main categories:
Natural Change
The ecosystems in the Rockies are young compared to global ecosystems. They are still recovering from the glaciations of the previous ice age. In addition, natural events like forest fires and floods continually change the landscape.
Forest fires can have complex effects on terrestrial ecosystems. In older forest stands, fire can open up the canopy, and thin the understory, allowing for the growth of young trees, helping to keep the demography of the forest healthy (a good mix of young and old trees). Fire can also help suppress forest disease and pests, by burning dead and dying trees, limiting the spread of disease from these sources.
Over longer timescales, natural processes will build the soil layer and erode the mountains. Glaciers typically scrape away all the soil, leaving bare rock or gravel. Over time, the natural establishment, growth, death, and decay of plants and animals rebuilds the soil layer. As the soil fertility and depth improve, different species can establish and grow, leading to gradual changes in the species present at a given location, a process known as ecological succession.
Land Use Change
The Rocky Mountains have been important to humans for as long as humans have been in the area. In the present day, we interact with the ecosystems in a multitude of ways. The Rockies are an important tourism destination, leading to the development of town sites and trails, as well as more complex impacts like ski resorts and golf courses.
Natural resource extraction is also prevalent in the Rockies. Oil, Coal, and Natural Gas are found in abundance in the former sea-bed sediments. The limestone found in the upper layers of the mountains can be used to create concrete, while the abundant forest cover of spruce and pine is valuable to the forestry industry.
Human activity often leaves a mark on the landscape, and as trees are cleared, earth moved, and rock and fuel dug up, the ecosystem around this activity responds and changes.
Climate Change
Globally, the rise in carbon dioxide content in the atmosphere is resulting in changes to the earth’s climate regime. These changes are most pronounced at high latitudes and elevations. Since the Canadian Rocky Mountains are both northern and high elevation, the effects of climate change are much more drastic here than the global average.
As of the year 2000, glaciers have lost approximately 25% of their area, and were smaller than they had been at any time in the last 3000 years. Winters have warmed at twice the rate of other seasons, resulting in changes to how precipitation arrives on the mountains slopes. With a warmer winter and earlier spring, we are seeing less snow and more rain. Rain-on-snow events quickly deplete the snowpack, leading to more scarce water late in the summer, and less insulation for organisms living under the snow.
Research Highlight
Alpine butterflies in a changing climate.
The Rocky Mountain Parnassius, a small white butterfly, can be found throughout alpine meadows in the Rockies. It relies on two plant species that are specialized to grow in alpine meadows. The butterfly lays its eggs in the fall on only two plant species. The eggs lie dormant under the snowpack, insulated from the harsh temperatures of winter at high elevation. In the spring time, as the snow melts, the caterpillars emerge and begin to feed on the plants that their parents chose for them. By mid-July, the caterpillars transform into butterflies, and begin to search for mates.
Photos clockwise: A Parnassius caterpillar feeding; Red Sedum; Yellow Sedum
Under a changing climate, scientists predict that the host plants for the Rocky Mountain Parnassius will struggle to persist as the meadows they rely on warm. As these plants begin to disappear, the caterpillars and butterflies will likely become more rare as well. In addition to the loss of plants, changes to snowfall patterns threaten caterpillar survival. In recent studies, scientists have found that low snow cover in November leads to fewer eggs hatching in the spring. This may be because the snow cover protects the eggs from the freezing during the first cold snaps. With less snow, eggs are more likely to freeze and die.