The plant life of Wyoming includes about 2,200 species that form a variety of grasslands, desert shrublands, forests, mountain meadows, and alpine tundra. Forests cover nearly one-fifth of the state, primarily at higher elevations where the annual precipitation is higher. In the lower mountains, such as in the Black Hills, the forests are dominated by ponderosa pine. Farther west, Douglas fir dominates the forests at lower elevations. The climate is cooler and wetter in the higher mountains, which is favorable for trees such as lodgepole pine, Engelmann spruce, subalpine fir, and aspen. The alpine timberline occurs at about 3,000 m (about 9,800 ft) in the northern part of the state, and at about 3,500 m (about 11,500 ft) in the south. Subalpine fir, Engelmann spruce, whitebark pine, and limber pine occur only as wind-swept shrubs at the upper limits for tree growth.
The alpine tundra above the timberline is dominated by a variety of grasses and other herbaceous plants, some of which also are found in the Arctic tundra. The temperature during the summer in alpine tundra can be quite warm during the day, but frequently it drops to below freezing at night.
Several species of sagebrush are characteristic of much of the lowlands in Wyoming. The most common species, big sagebrush, forms extensive shrublands in the western two-thirds of the state. Western wheatgrass, blue grama, needleleaf sedge, Indian ricegrass, junegrass, scarlet globemallow, fringed sagewort, phlox, milkvetch, rabbitbrush, and pricklypear cactus are also common. The grasslands in the eastern part of the state are dominated by the same species and others, but sagebrush is less common.
Greasewood is a shrub that occurs in low areas that have standing water in the spring, but which become dry salt flats later in the summer.
In the driest environments, where the annual precipitation is less than 200 mm (8 in), desert shrubs such as saltbush, winterfat, and spiny hopsage occur with various species of sagebrush. Juniper and mountain-mahogany are common shrubs on ridges and in the foothills of the mountains, often occurring with limber pine or ponderosa pine. The most luxuriant plant growth in the lowlands occurs along streams and rivers, where the soils are wetter for a longer time during the summer.Cottonwood trees and a variety of shrubs, especially willows, are widespread in these riparian environments. Blue spruce, alder, and box elder occur with the cottonwood and willows in some areas. "Wyoming" © Emmanuel BUCHOT, Encarta, Wikipedia.
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