treelines

Treelines are ecological boundaries at the edge of where trees can grow, marking the transition between forested areas and tundra or barren alpine zones. They occur in two main contexts: Arctic treelines, which delineate the limit of forest growth at high latitudes, and alpine treelines, which cap forest growth at high mountain elevations. Above these limits, conditions become too harsh for sustained tree growth, and vegetation shifts to low, shrub-dominated or herbaceous communities.

The position of a treeline is determined primarily by climate, especially the length and warmth of the growing season and the risk of freezing temperatures. Other factors also play a role, including soil depth and moisture, permafrost presence, wind exposure, snow cover, and disturbance regimes such as fire or avalanches. In exposed areas near treelines, trees often take on stunted or deformed forms known as krummholz, shaped by wind and cold.

Forest species involved vary by region but commonly include cold-tolerant conifers such as pines, spruces, firs, and larches, with deciduous birches and willows occurring near the boundary in some areas. The treeline forms an ecotone between established forest and the more open, tundra-like zones, influencing habitat structure, biodiversity, soil development, and local hydrology.

Climate change is affecting treelines in many regions, with warming temperatures allowing trees to establish at higher elevations or latitudes. This upward or poleward shift can alter species composition, carbon storage, and ecosystem processes, and may reshape alpine and boreal landscapes over coming decades.