timberline

Timberline refers to the upper boundary of a landscape capable of supporting tree growth. In mountains it marks the altitude beyond which climatic conditions prevent trees from establishing or surviving. The term is closely related to treeline; in some contexts timberline is used for the practical limit for timber production, while treeline denotes the natural physiological limit for tree growth.

Timberline occurs worldwide in major mountain ranges and boreal regions. Its altitude varies with latitude and slope, typically ranging from about 1,800–2,500 meters in some tropical regions to over 3,500 meters in high-latitude ranges. Temperature, length of the growing season, wind exposure, soil depth, moisture, and permafrost all influence the line.

Ecologically, timberline supports subalpine and alpine communities, including krummholz—trees that are shaped and stunted by harsh winds and cold. The boundary can be sharp or diffuse, and trees near the line are often slow-growing and misshapen by environmental stress.

Climate change has been linked to upward shifts of timberline in many mountain regions, as warming creates conditions favorable for tree growth at higher elevations. This relocation can alter alpine biodiversity, hydrology, and fire regimes, with cascading ecological effects as species migrate.

In forestry, timberline may also denote the upper limit for economically viable timber production, a practical concept distinct from the natural treeline.