3.The disturbance hypothesis Wind effects on plant growth c dam Wind effects on local treeline formation Avalanches on and the char Mortality mal disturbances 55 Mechanic damage by wind, ice blasting, snow break and avalanches, fire…… 3. The disturbance hypothesis Animal disturbances such as herbivory: Fungal pathogens; Man-made impacts such as grazing Tranquillini, W. 1979. Physiological Ecology of the Alpine Timberline Helianthus annuus Wind effects on plant growth Martin & Clements, 1935, Plant Physiol. 10, 613-636 0 5 10 15 • The altitudinal position and the character of the treeline may be wind￾determined, i.e. the altitudinal limit of tree growth is lowered by strong and regular winds. Wind effects on local treeline formation Rocky Mountains National Park Avalanches Animal disturbances Mortality Fate of seedlings of Picea abies (Norway spruce) in a subalpine spruce forest after the first winter. Most individuals were killed by the Herpotrichia nigra (snow mould) and by mice. A dense web of Herpotrichia nigra hyphae around a low branch of small spruce. The parasitic fungus grows preferably in air pockets around branches in the snow