A geographical model for the altitudinal zonation of mire types in the uplands of western Europe: the example of Les Monts du Forez in eastern France
Résumé
The geographical distribution of mires in the oceanic mountain ranges of western Europe cannot be explained without bringing together a number of physical and human factors. In Les Monts du Forez, which are granitic and metamorphic mountains covering an area of 1800 km2 and rising to an altitude of 1634 m in the east of the French Massif Central, a series of mires on long slopes reflects the effects of changing combinations of these factors with altitude. The scale of variation falls within the limits of bioclimatic levels and is manifest as: the absence of mires at foothill levels below 900 m; small mires of anthropogenic origin and remnant peat at lower mountain levels between 900 m and 1100 m; peat systems where evolution has been more or less affected by human intervention at median mountain levels between 1100 m and 1250 m; large ombrotrophic mires, often naturally convex and dating from the first half of the Holocene epoch, at upper mountain levels between 1250 m and 1450 m; and small established mires that are more or less directly linked to human intervention at sub-alpine levels above 1450 m. The role of human societies appears to dominate, with exceptions in the upper mountain levels. Human influence presents in two forms, both of which are related to the old traditional farming methods of the region: the first is destruction of mires, mostly by drainage, and the second is mire creation through modifications of the hydrology of the valley floor and the vegetation cover. This spatial and multi-factor distribution of mires is a component that should be taken into account in relation to their conservation management.