(Baumgrenze) The more or less clearly defined region at high latitudes (the taiga/tundra boundary) or high altitudes (the subalpine/alpine boundary) beyond which trees do not grow. Occasionally inverted tree lines are seen in which trees do not grow below a certain line as, for example, in frost hollows. The limits to tree growth are presumably set by some climatic factor though it is by no means certain which particular factor is operating. Numerous theories have been advanced based on different climatic variables such as heat, light, or carbon dioxide deficiency, excessive wind or snow depth, etc. A recent theory suggests that, beyond the tree line, leaves become desiccated in winter because the summer growing season is not long enough to allow the leaves to mature fully and resist water stress. Compare timber line. |
