The upper timberline is the most conspicuous vegetation limit in high-mountain areas of all continents, except for the Antarctic. Timberline also is an important ecological boundary, marked by a change in site conditions and plant communities when crossing the forest limit. No other vegetation limit has a comparable effect on the high mountain environment. No wonder that timberline has always attracted research for scientific and practical reasons. In view of the fact that climatic timberline is mainly caused by heat deficiency, early researchers mainly focused on thermal conditions at timberline. They found some coincidence between the altitudinal position of timberline or tree line and mean temperature of the warmest month, the three or four warmest months (tritherm or tetratherm), and the total sum of temperature of the growing season. However, there are many other local and regional studies on high-altitude forests, on the requirements of the tree species forming the timberline, on forest history etc. Although mainly descriptive, they all contribute to a better understanding of the causes of timberline.
