Geoecological Aspects of the Upper Timberline in Tenerife, Canary Islands

The only timberline tree in Tenerife is Pinus canariensis, a three-needled pine endemic to the western Canaries. The average timberline elevation of 2000 to 2100 m on Tenerife is extremely low for this subtropical latitude. In unprotected sites near the timberline there are two critical seasons for reproduction: the summer with intense radiation, overheating, and dessication of the ground; and the winter with short-term weather variations, frequent nightly freezing, and frost-induced soil movements. Seedlings and young trees are extremely sensitive to the critical ecological factors which include temperature and moisture. Under natural conditions a quasi stability of the actual timberline is likely. The history of vegetation indicates a regression of the tree distribution in the recent past. There is evidence for the extinction of a preexisting Juniperus woodland belt. Human impact on the timberline environment was destructive for a long time through wood and shrub cutting or grazing activities, but has become constructive in recent years with large-scale reforestation. The timberline of Tenerife shows a marked individuality, which raises serious problems for geoecological comparisons with other subtropical mountain areas.