The climatic overlap of the pacific and arctic air masses over Kluane National Park & Reserve has resulted in one of the greatest diversity of plants and wildlife in northern Canada. A montane forest of white spruce, trembling aspen and balsam poplar covers much of the lower valleys and slopes. Treeline is at 1050 to 1200 m (3,500 to 4,000'), depending upon local conditions. Low-growing or stunted shrubs in the transition zone include: willow, dwarf birch, and alder, which provide protection for the smaller plants. Summers in alpine tundra (generally above 1400 m or 4600') are a flourish of colour, with over 200 varieties of alpine flora.