Trees that grow at high elevations are adapted to this environment. The high-elevation environment is characterized by higher light intensity (when clear) and proportion of ultraviolet radiation, lower absolute humidity (which favours water loss) and carbon dioxide content, frequent high winds, and greater daily temperature fluctuations, radiation of heat out into space (especially at night), and precipitation (although some alpine areas are subject to drought at times). Any or all of these factors can interact to bring about unique formations. For example, cold air drainages at the crest of valleys can cause a local depression of timberline. The reason low temperatures affect timberline is that they slow biological processes, which decreases the production of dry matter, a condition that is exacerbated by the shortened growing season. As a result, fewer of the cells, tissues, and storage molecules that are needed for annual growth and reproduction are formed. If the growing season is shortened too much, the optimum amount of supportive tissue may not be formed.

The covering layers of the tree surface also are important in resisting environmental stresses. The biotic stress and inadequate energy production and allocation that occur when temperature is sufficiently low may impair the optimum development of these superficial layers and increase the vulnerability of the tree.

Seed production requires energy reserves that may not normally be available each year. The interval between good seed years increases with elevation and latitude. It is another important aspect of survival in the cold at high elevation, although species at high elevation compensate for this somewhat by relying more heavily on asexual reproduction. Thus, the tree line may be considered to be an equilibrium space between the forces of regeneration upward and mortality downward.