Timberline Fluctuations

The previous chapters have provided a first insight into the heterogeneity, complexity and great physiognomic and ecological variety of the timberline phenomenon; a heterogeneity and variety that largely have faded out when scientists mainly focused on the one factor (mainly temperature) controlling the altitudinal position of timberline and on the physiological response of tree growth to the timberline environment. Spatial and temporal timberline structures reflect past and on-going changes caused by many external (e.g., macroclimate, effects of altitude) and internal factors specific to the ecotone (microclimates, soil conditions, succession, competition of trees and other vegetation, animals, ecological properties and requirements of the timberline forming tree species and others) interacting in a complex way. Topography is the only almost constant factor among them, if not affected by sudden changes due to landslides and similar events, for example, or when considered in geological terms. Mountain topography (convex, concave, gentle, rugged, smooth, etc.) determines the basic pattern of the spatial timberline structures (distribution of trees, soil moisture, soil temperatures, etc.) also under the influence of changing climate (Holtmeier and Broll, 2005).