Rôle de la nutrition minérale et de l'approvisionnement en eau sur la croissance du pin laricio de Corse dans l'ouest de la France

Abstract

The importance of mineral nutrition and soil water regime (water soil reserve index and lateral water supply) for the radial growth of 1 808 mature Corsican pines (Pinus nigra Arnold ssp laricio Poiret var corsicana) (average age = 30 years) sampled in 183 sites in western France (Pays de la Loire region) was studied. Foliage and chemical soil analyses indicate that growth depends exclusively on phosphorus nutrition. The optimal P foliar concentration is 0.15% (N/P foliage ratio = 10), the critical value is 0.12% (N/P = 14) and the deficiency level is 0.10% (N/P = 18). Needle content of other nutrients is sufficient for tree requirements and does not differ between trees with different growth levels. The average concentrations are 1.59%, 0.19%, 0.12% and 0.59% for N, Ca, Mg, K, respectively. The response of trees to phosphorus is greater on moist sites than on dry sites, but considerably decreases during drought periods. Soil water regime, which is found to predispose trees to climatic variations, may locally accentuate the effects of exceptionally dry years and hence induce durable radial growth decrease and subsequently forest decline. However, low competition between trees seems to be able to decrease the intensity of dryness by minimizing water competition within stands. In order to improve the radial growth of Corsican pine plantations, the best advice is to avoid this species on sites clearly unfavourable for mineral nutrition and/or for water supply, and to apply an adequate silviculture (regular thinnings) in order to minimize water competition between trees, especially during climate crisis.