During the last Ice Age, the Cariboo Mountains of northern Wells Gray acted as a major dividing line to the ice sheets of inland British Columbia: the glaciers to the north moved northward, and those to the south, southward.
When the glaciers later retreated, here about 10,000 years ago, they were followed by advancing armies of colonizing plants. Some of the plants had waited out the Ice Age south of the ice margin, and so followed the melting ice northward. Others moved southward from glacial refugia in Alaska and the Yukon. Because the Caribou Mountains represented a last stronghold of the Pleistocene glaciers, it was here that many of the southern and northern invaders first met.
This mix of northern and southern elements has endowed the Clearwater Valley with an unusually rich vascular flora. To date, more than 1000 species of trees, shrubs and herbs have been recorded, and there is reason to suppose that another few hundred additional species might eventually be added to this total. “New” species to the park are being discovered every year.
One group of plants not particularly well represented in Wells Gray is the rare and/or endangered element. Because glacial ice covered the park until relatively recently, relatively few plants occur here that do not also occur – often abundantly – elsewhere in the province.
Still, rarities do pop up from time to time, including the Adders’ Tongue Fern (Ophioglossum vulgatum), Mingan Grape Fern (Botrychium minganense), Crested Shield Fern (Dryopteris cristata), Downy Oat Grass (Danthonia sericea), Teachers’ Sedge (Carex praeceptorum), Few-flowered Spike-rush (Eleocharis quinqueflora), MacCabe’s Violet (Viola maccabeina), Wind-river Whitlow-grass (Draba ruaxes), and Oregon Willowherb (Epilobium oregonense).
Owing to the moister, cooler weather at higher elevations, oldgrowth forests are a common feature of timblerline throughout the park, even in the south. The oldest timberline trees in the Trophy Mountains, for example, are approximately 250 years in age, though it’s now clear that the forests containing them are much older, in some cases possibly thousands of years in age. When fire (or loggingœ) does extend to timberline, the forest may take many decades to regenerate, in the mean time creating temporary subalpine meadows. The clearcut “forests” at the top end of the Trophy Mountain road, for example, date from logging in the 1980s; in principle they should be ready to log again in about 50 years. See what you think.
Plants in Mountainous Terrain
Among the most important factors controlling the distribution of plants is climate. Climate is just weather writ long-term. In Wells Gray, climatic conditions at valley bottom are very different from those in the mountains, so perhaps it is not surprising that the plants are different too.
As you go up a mountainside, especially during the growing season, the overall climate takes a turn for the cool – just as it does when you go north. On the mountain, however, climatic change is much more abrupt, so that for every 110 m you climb, you are, in a sense, moving northward 1° of latitude.
Many of the plants that cling to the barren summits above treeline are essentially plants of the arctic. They survive at this latitude only because mountains rise high enough to approximate arctic conditions – again, at least during the growing season. At treeline and below, temperatures are more moderate, and the climate more resembles a boreal climate. Boreal, too, is the vegetation – which here consists primarily of conifer forests and, in the understory, copious mosses.
Virtually all of Wells Gray’s plants can be described as belonging to either the arctic zone or the boreal zone. The only exceptions are those restricted to the warmest valley bottoms; these might better be thought of as outliers from the temperate zone farther south.
The broad life zones just described can be divided into subzones, each characterized by its own assemblage of plants. In all, there are eight subzones in Wells Gray. With practice, you’ll soon learn to recognize them using various indicator plants, including trees and shrubs.
For more information on the flowers and trees of the Clearwater Valley, see this updated on-line checklist of vascular plants in and around the park.