A COMPARISON OF THE ECOLOGY OF PEDUNCULATE AND SESSILE OAKS - RADIAL GROWTH IN THE CENTER AND NORTHWEST OF FRANCE

The aim of this study was to find out if the great difference in behaviour between pedunculate oak and sessile oak in terms of decline (described previously) also appeared in terms of radial growth. and, if so, which ecological variables were concerned. One hundred seventy-three plots were chosen throughout an extensive area of France, covering a wide range of climatic and pedological conditions. The spatial distribution of pure stands of the two species is not random, which led us to assume that pedunculate oak has greater nutrient and water requirements than sessile oak. This was confirmed in the investigation of mixed high forest stands, where. on average, the radial growth of sessile oak is 46% higher than that of pedunculate oak. This gap is even wider, as local conditions of mineral nutrition and, more importantly, water supply worsen. Moreover, after an exceptional drought, the average difference is still greater for several years. On the other hand, sessile oak is more sensitive to low average temperatures during the growing season. Pedunculate oak has an advantage regarding some variables linked to wood quality (sapwood width and wood density), even if trees with the same diameter and average annual growth are compared. In order to improve the productivity of French oak forests in the area concerned, the main advice is to eliminate pedunculate oak in sites clearly unfavourable to the mineral nutrition and/or water supply of the trees. In less unfavourable sites, pedunculate oak may be retained. mainly in the coldest regions, but it should be grown in low density high forest. In intermediate conditions. the better wood properties of pedunculate oak could be taken into account when choosing the species to be favoured.