Zone, is found in the low to middle elevations of the Columbia Mountains in southeastern British Columbia, west of the Rockies, as well as north in the Nass and Skeena River drainages. The cool, wet winters and warm, moist summers produce the greatest plant diversity of any zone in the province. Western Hemlock and Western Redcedar predominate, but Grand Fir, Western Larch, White Spruce, Engelmann Spruce, black cottonwood, trembling aspen, Western White Pine, and Subalpine Fir are also common, depending on the elevation. The dense and diverse forests make this zone the second most productive forest zone in British Columbia and Canada. Sub-Boreal (Hemiboreal) Spruce and Pine-Spruce Zones: The central interior of the province, consisting of the rolling lake-studded terrain of the Cariboo — the Fraser and Nechako Plateaus — is characterised by severe, snowy winters and warm, short summers. This is a transitional zone between southern and northern biomes. Seral species include Lodgepole Pine, Rocky Mountain Douglas-fir, and trembling aspen; mature species include White and Engelmann Spruce, and Subalpine Fir. The moderately dense forests are interrupted in places by ponds and muskeg. The generally flat plateaus make this an active area for logging. Boreal Zones: The northern third of the province is dominated by long, cold winters, and short, warm summers. This is a vast, largely unpopulated region, with isolated logging and mining activity. White Spruce, Black Spruce, Lodgepole Pine, trembling aspen, Tamarack Larch, and Paper Birch predominate among the meadows and muskeg of the Peace and Liard Plains. At higher elevations, the winters are harsher, the summers briefer, and White Spruce and Subalpine Fir give way to scrub willow and birch. Mountain Zones: At higher elevations (above about 850 m on the southwest coast, less as one goes farther inland and north), the summers are shorter and the winters are colder. Along the coast, the lush, diverse forests give way to more uniform stands of Mountain Hemlock, Pacific Silver (Amabilis) Fir, and Yellow Cedar. These are interrupted by subalpine heaths, meadows, and fens. In the drier, interior regions, the higher elevations are marked by Engelmann Spruce, Subalpine Fir, Subalpine Larch, and Lodgepole Pine, the trees clumped among meadows and grassland. Floristic province In botany, nearly all of British Columbia is part of the Rocky Mountain Floristic Province. Political geography Founded as several colonies as part of the British Empire, the political geography is complicated by the fact that