Alpine plants are plants that grow in an alpine climate, which occurs at high elevation and above the tree line. There are many different plant species and taxa that grow as a plant community in these alpine tundra. These include perennial grasses, sedges, forbs, cushion plants, mosses, and lichens. Alpine plants are adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, wind, drought, poor nutritional soil, and a short growing season. Some alpine plants serve as medicinal plants. Ecology Alpine plants occur in a tundra: a type of natural region or biome that does not contain trees. Alpine tundra occurs in mountains worldwide. It transitions to subalpine forests below the tree line; stunted forests occurring at the forest-tundra ecotone are known as Krummholz. With increasing elevation, it ends at the snow line where snow and ice persist through summer, also known as the Nival Zone. Alpine plants are not limited to higher elevations. However, high-elevation areas have different ecology than those growing at higher latitudes. One of the biggest distinctions is that the lower bound of a tropical alpine area is difficult to define due to a mixture of human disturbances, dry climates, and a naturally lacking tree line. The other major difference between tropical and arctic-alpine ecology is the temperature differences. The tropics have a summer/winter cycle every day, whereas the higher latitudes stay cold both day and night. In the northern latitudes, the main factor to overcome is the cold. Intense frost action processes have a profound effect on what little soil there is and the vegetation of arctic-alpine regions. Tropical alpine regions are subject to these conditions as well, but they seldom happen. Because northern alpine areas cover a massive area it can be difficult to generalize the characteristics that define the ecology. One factor in alpine ecology is wind in an area. Wind pruning is a common sight within northern alpine regions. Along with wind pruning, wind erosion of vegetation mats is a common sight throughout Alaska. Growth Long-lived perennial herbs are the most common type of plant in alpine environments, with most having a large, well-developed root and/or rhizome system. These underground systems store carbohydrates through the winter which are then used in the spring for new shoot development. Some species of saxifrages have small root systems, but are evergreen. The leaves of these plants store energy in