Physiognomic and Ecological Differentiation of Mountain Timberline

Abstract

A mosaic of tree clumps, scattered groves, isolated, more or less deformed tree individuals and treeless patches covered by low shrubs, herbs, and grasses characterizes the timberline ecotone. It depends on the geographical position of a mountain range whether the treeless communities consist mainly of dwarf shrubs and grasses (e. g., European Alps), dwarf shrub-lichen heath (fjell, Fennoscandia), mountain steppe (arid zone) or tussock grassland (e. g., in the tropics, New Zealand). Which and how many tree species occur at timberline depends on the climate zone and on the history of floral development. If timberline is formed by more than one species, the different ecological properties and requirements of the species (e. g. shade tolerant and intolerant, pioneer or climax species, animal or wind mediated seed dispersal, etc.) may play an important role as to the development of the tree stands, and also in respect of structure, physiognomy and climatically induced shifts of timberline. Competitive species such as beech (Fagus sylvatica), Norway or Engelmann spruce (Picea abies, Picea engelmannii), for example, often form dense stands and abrupt timberlines, while in the case of less competitive species such as larch, most pines or juniper forests are comparatively open giving way gradually to grassland or other alpine vegetation (e. g., Walter, 1968; Armand, 1992; see also Photos 12 and 13). Some authors call such forests “open forests” (e. g., Kessler, 1995; Miehe et al., 1998).