A line through the last of the stunted trees, forming the latitudinal or altitudinal limit beyond which the climate is too cold for trees to grow. This is normally the region where the mean summer temperature is lower than 10 °C. The tree line marks the boundary between tundra vegetation and the bare rock, snow, and ice of the high Arctic and Antarctic. On mountainsides the height of the tree line varies with latitude (i.e. it is higher in the tropics than in higher latitudes) and climate type. Trees below the tree line are erect and grow in dense stands. Trees close to the tree line are sparsely scattered and prostrate or nearly so. See krummholz.
Subjects: Plant Sciences and Forestry — Ecology and Conservation.