Above 10,000 feet the pattern of life changes. Until timberline is reached at about 11,500 feet, this band of mountain country is called the Sub-Alpine or Hudsonian life zone. Soil and moisture conditions are almost as favorable as in the lower montane zone, but here the snows of winter stay late, especially on north slopes, and frost may come even in mid-summer. The race to ripen seed, before winter comes, is intense, and the seeds, when produced and scattered, face special problems of germination and survival.

The trees of this zone are largely Engelmann spruce, limber pine and alpine fir. Some thick forest stands exist, but the main pattern is small compact tree groups—one or more big seed-trees surrounded by younger offspring—with open patches of grass between. Perennial flowering plants, springing from woody root-crowns have special advantages here, though some annuals thrive, especially if they can get started in the fall and remain dormant under snow till spring. Melting snows in May, June and early July give natural irrigation to large areas of this zone. Competition with sedges and grasses and ability to stand light frost are problems for the plants that live here. Many typical alpine plants of the next higher zone work down into these sub-alpine meadows.

The picture at the top of this page was taken just west of the Poudre Lakes in Rocky Mountain National Park. Lake Irene is in the foreground.