Régénération en altitude de l'épicéa (Picea abies (L) Karst) sur les souches dans les Alpes françaises

Abstract

High-altitude regeneration of spruce on old stumps in the French Alps. Regeneration of spruce forest is very difficult above an elevation of 1,500 m. However, young saplings can often be observed growing on old stumps. The aim of the present study is to provide new information on the decomposition of wood and its colonisation by plants, particularly young trees. A literature review is provided and the area under study is detailed: the middle and high Tarentaise valley and the high Isère valley, in the Northern French Alps. The analysis of the forest was carried out on areas measuring 10 x 100 m, and each stump is reported on the map. The stumps have been sorted into 5 categories according to their degree of decomposition: I, very recent, intact stumps; II, recent stumps, the bark having peeled away with the establishment of the first plants; III, older stumps with a more extensive plant colonisation and considerable establishment of young trees; IV, old, highly decayed stumps, almost complete plant colonisation and many conifer saplings; V, very old and hardly visible stumps, completely covered by vegetation (mainly Vaccinium myrtillus), the saplings being less numerous than in category IV. The development of these 5 stages depends on the ecological conditions prevailing on the site. In spruce forests where there is a high grass cover, the seedlings do not establish on stumps; and where there is bilberry coverage they seldom do so either. At lower elevation spruce forests, they are very often established on stumps, as is the case in forests exposed to the south. In order to facilitate regeneration it is recommended that the forest floor is raked so as to mix wood debris into the soil.