Glacier National Park
Glacier is the meeting place for a variety of plant communities. A total of five floristic provinces have been identified in Glacier. Many of the plants typical of the northern Rocky Mountains, Pacific, and northern (Boreal) regions reach their northern, eastern, and southern limits here. And, of course, the rising of the Rocky Mountains along the East Front creates the western limits of the Great Plains. The fifth floristic province is found above the 7000-foot (2100-m) elevation where a fifth distinct plant group, comprised of alpine plants, grows in the rockiest, highest part of the park – forming "disjunct" or isolated arctic communities.
The geographic location of Waterton-Glacier on the 49th parallel and the narrowness of the Rocky Mountain chain at this point contribute to the diversity of the region's vegetation. Glacier is at the center of a botanical watershed, a point separating plant communities common to the south from those in the northern ranges. As a result, many species are at their extreme limits of distribution.
Also, due to the narrowness of the mountains at this location, the Continental Divide lies very close to the Great Plains allowing for expanses of prairie to exist within park boundaries. A strong Pacific Northwest Coastal influence can be found in the Lake McDonald Valley west of the Continental Divide where approximately 100 Pacific coast plant species have been identified.
Weather patterns contribute to this diversity of vegetation in Glacier. Of particular interest is the Inland Maritime Climate that prevails in some western valleys of Glacier. This is the eastern most penetration of this weather pattern, and it results in higher precipitation and moderate winter temperature. The Pacific Maritime influence has created opportunities for plant species more often associated with the coast to gain a foothold in the Lake McDonald valley on Glacier's west side. East of the mountains, continental air masses coming out of the Arctic dominate in the winter, with subzero temperatures being common. The eastern slopes are located in the mountains' rain shadow, resulting in decreased precipitation and drier growing conditions. Also, the eastern valleys are subject to high downslope winds in both the summer and winter. These winds have a marked drying effect on plant communities.
Waterton Lakes National Park
Despite Waterton's small size (202 sq. mi/525 sq. km), it has a world class bounty of plants. With 970 species of vascular (higher) plants, it has more variety than Banff or Jasper. Waterton also has an unusually high number of rare plants – about 175 provincially rare (e.g., western trillium, mountain lady's-slipper, Macloskey's violet, pink meadowsweet); over 50 nationally rare, of which more than 30 are found nowhere else in Canada but Waterton (e.g., mountain gentian, Jone's columbine, pygmy poppy, mountain hollyhock). Note: some of these species are also found within Glacier National Park.
Many unusual plants in Waterton like beargrass, devil's club, Macloskey's violet and western trillium are more common west of the Continental Divide. This occurs because the prevailing Pacific weather systems spill over the divide, bringing moister conditions and windborne seeds to Waterton. It is no coincidence that Waterton has six different species of anemone or windflower, for wind is the prevalent influence in the park.
The combination of Waterton's geographic situation, its topography (mountain and prairie) and its mild, moist, windy climate has created a wide variety of growing conditions within a very small area. Geologically, the Waterton area was very close to the southern edge of the continental ice sheet, so that glacial refugia for plants ("refuges" for plants and seeds that were not covered with ice) were not far away. This resulted in the dispersion of a large number of species into the area as the ice melted back.
- Mountain plants, common in Banff and Jasper, that do not extend much further south;
- Plants more common south of the border that creep into Alberta only in the Waterton area;
- Plants common west of the divide which have spilled over into Waterton because of prevailing Pacific weather systems; and
- Prairie plants at the western limit of their range.