Standörtliche Differenzierungen im subtropischen Sukkulentenbusch der Kanareninsel Teneriffa

The lower part of the island is characterized by large areas of exposed rocks, volcanic cinders and dust, and by more or less scattered plants and vegetation units. Many of these plants are adapted to dry conditions with candelabra-like stems and leaf succulents. This zone extends from sea level up to about 400 m in the north and considerably higher (800 m up to 1000 m) in the south and southwest. Several endemic species of Euphorbia predominate the xerophytic shrub zone, undoubtedly the most spectacular being the tall, cactus-like Cardon (Euphorbia canariensis). Other common shrubs are e. g. Euphorbia balsamifera, E. aphylla and E. obtusifolia ssp. regis-jubae. Another three species (E. atropurpurea, E. obtusifolia ssp. obtusifolia and E. bourgeauana) are more restricted in distribution. A further common plant which occurs here is Kleinia neriifolia, a thickstemmed succulent (Cichoriaceae). This xerophytic scrub is a more diverse community or vegetation complex with many additional species of plants. Some of the cliff areas, particularly those of the older Tertiary basalts and phonoliths in the Anaga and Teno region, harbour relict local endemics which often have their greatest affinities to species of the Sudano-Arabian region. The aims of this study are to arrange the material from relevés of the Euphorbia canariensis scrub zone of Tenerife to provide a comparison by means of variability and similarity of this association group. The homogeneity of the Euphorbia canariensis scrub is due to the comparatively uniform ecological conditions; differences within this vegetation type are caused by vegetation history (endemics) and the available water content of the volcanic soils. Four different associations can be found: Ceropegio fuscae-Euphorbietum balsamiferae Rivas-Martinez, Wildpret et al. 1993, Periploco laevi gatae-Euphorbietum canariensis Rivas-Martínez, Wildpret et al. 1993, Ceropegio dichotomae-Euphorbietum aphyllae Rivas-Martinez, Wildpret et al. 1993 and Euphorbietum atropurpureae Lems 1968. There is a possibility of multidimensional diversification and classification of this vegetation type. The transition zone between the arid scrub zone and the Canarian pine and laurel forests was occupied in the past by open woods including the "Sabinar" (Juniperus phoenicea ssp. canariensis). The Canary palm (Phoenix canariensis) and the Dragon tree (Dracaena draco), plants of the upper parts of the lower xerophytic zone, are now rarely found growing wild. Amp