The treeline could then coincide with the position of an isotherm (mean air or soil temperatures) above which trees could not exist. Theoretically, on an ideal smooth, uniform slope with uniform climate, and soil, the treeline would run parallel to the contour lines. Subalpine forests and the treeline ecotone are strongly influenced by abiotic (e.g., climate, landslides, avalanches, soil erosion, wild fires) and biotic factors (defoliating insects, herbivores, bark beetles). The width of the ecotone may vary considerably in dependence from the local conditions. The transition zone is characterized by a mosaic of usually scattered and climatically stunted groups and solitary trees interspersed with patches of subalpine or subarctic/arctic vegetation. Treeline is the transition zone (ecotone) reaching from closed subalpine or northern forests to the outliers of tree growth in the mountain or arctic tundra. Effective measures to reduce or prevent abiotic and biotic disturbances of high-elevation forest may contribute to greater safety for people living in the endangered areas of the mountain valleys and also improve other ecosystem services of the subalpine forest.Ībiotic Disturbances, Biotic Disturbances, Human Impact Both natural and anthropogenic disturbances may counteract positive influences of climatic warming on subalpine forests and treeline. A subsequent absence of natural disturbances may also be considered a disturbance initiating a new development. Subalpine forest may recover from disturbance or become replaced by a substitute formation (e.g. Due to man-caused habitat fragmentation, the animals’ impact on the remained habitats has increased. Inadequate game management is the primary cause of intolerable ungulate numbers. Oversized populations of wild ungulates impede tree regeneration and can cause local soil erosion. Cyclic or episodic mass outbreaks of defoliating insects and bark beetles, and pathogens also cause severe disturbances. Wild fires are likely to increase as a result of warming climate and would possibly prevent climatically-driven treeline advance. Forest destruction by fire is often followed by soil erosion. Fires have played a major role in the removal of high-elevation forests. External factors, like cyclonic storms, may cause fundamental disturbances. Hazards will probably increase due to climate change. Consequently, avalanche destructive potential has increased. Removal of the upper subalpine forests by humans has enlarged the snow-catchment area of avalanches and elongated the avalanche pathways. Disturbances by mass movement and avalanches give the subalpine forest and the treeline ecotone a distinct spatial pattern characterized by forest on safe topography and sites that preclude forest. Both abiotic and biotic factors may cause reversible or irreversible disturbances. This article considers disturbances caused by abiotic and biotic factors and human impact in the ecological region extending from subalpine forest to the upper tree limit. Received: ApAccepted: JPublished: June 29, 2018 This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). 1Institute of Landscape Ecology, University of Münster, Münster, GermanyĢInstitute of Geography, University of Osnabrück, Osnabrück, GermanyĬopyright © 2018 by authors and Scientific Research Publishing Inc.
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