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Alnus viridis expansion contributes to excess reactive nitrogen release, reduces biodiversity and constrains forest succession in the Alps
Journal
Alpine botany
Volume
124
Number
2
Pages / Article-Number
187-191
Keywords
Alder, Alps, Browsing, Land use, Nitrogen fixation, Shrub encroachment
Abstract
Reduction in land use and complete land abandonment are widespread in mountainous regions and are mainly driven by socio-economic factors. Following land-use decline, shrubs and trees expand rapidly into montane and subalpine grassland and alter ecosystem properties at a large scale. In particular, the N-2-fixing shrub Alnus viridis is currently spreading at a breath-taking speed and thereby reduces biodiversity, leads to substantial reactive nitrogen enrichment and suppresses species succession towards coniferous forests across large areas in the Alps. In addition, this shrub vegetation neither protects against avalanches nor does it secure slopes from erosion. The expanding, monotonous A. viridis shrubland is impenetrable for hikers and diminishes scenic beauty and touristic value of the landscape. Actions and management adaptations are needed to halt the expansion of A. viridis. Goats and the traditional sheep breed Engadine sheep proved to be very effective in preventing and reverting shrub expansion because of their specific browsing behaviour.
