Sciences, Eaux & Territoires (Oct 2010)
Gestion multifonctionnelle des forêts de montagne, quels compromis entre les fonctions de protection et conservation ? Multifunctional management of mountain forests, compromises between the protection and conservation functions
Abstract
Les caractéristiques structurales de la forêt de montagne changent en fonction de son stade d’évolution. Ces changements impactent fortement deux fonctions-clé : la conservation de la biodiversité et la protection contre les risques naturels. Quels sont les stades les plus favorables à l’une ou l’autre de ces fonctions ? Est-il possible d’optimiser la réalisation de ces deux fonctions dans l’espace et dans le temps ? Cette étude apporte des éléments de réponse.Mountain forests are multifunctional forests that play a key role both on biodiversity conservation and rockfall protection. Most of these forests are under a process of secondary succession, where we can distinguish several stages with well differentiated diametric structures. These diametric structures strongly influence the two functions of biodiversity conservation and rockfall protection. The advanced stages of succession, representing mature forest, are the most important stages for conservation. The first one, so-called ageing stage and still dominated by the initial cohort, contains numerous very large dominant trees. The two following ones, so-called renewal and irregular stages, are very heterogeneous in terms of tree dimensions. The most effective stages to protect from rockfalls are the densest stages, i.e. the first stage of the succession, so-called initial stage, and the irregular stage. In certain mountain forest contexts, the irregular stage which optimizes the two functions is difficult to perennialize for forest managers. Consequently, when the function of protection is a priority, it is recommended to anticipate the renewal of the stands by creating openings large enough to promote a new succession (from 0.1 to 0.5 ha). Forest management then organizes the spatial and temporal distribution of these openings on a forested slope and aims at creating a perennial mosaic of small groups of trees at initial, intermediate (self-thinning) and ageing stages. The latest stages of the succession, the most interesting in terms of biodiversity, are often under-represented within this forest mosaic. The installation of small islands of sensible located old growth stands makes it possible to compensate for this under-representativeness.
