No abstract

RésuméPour étudier ce dépérissement, une méthode facilitant l'interprétation des différences d'état de santé entre peuplements a été retenue. Huit

RésuméLe travail présenté ici fait suite à un article publié dans cette revue (L EMOINE et al., 1986)

The carbon isotopic composition (delta(13)C) of wood and leaf cellulose of beech trees (Fagus sylvatica L.) was studied at 80 sites in northeastern France. We sampled sites with contrasting water balance, depending on soil type and precipitation. We tested the hypothesis that inter-site variations in plant delta(13)C reflect the spatial distribution of soil water availability, and we assessed whether delta(13)C could be used as a bioindicator of soil water availability. Patterns of variation in delta(13)C were compared with estimates of monthly water balance and with other soil characteristics. Between-site variability in delta(13)C was high (2.9 per thousand range in wood cellulose, 2.1 per thousand in leaf cellulose), but variation in water availability appeared to be only a minor factor contributing to this variation in delta(13)C. Unexpectedly, spatial variations in wood and leaf cellulose delta(13)C were significantly and positively related to soil fertility expressed by soil pH (r = 0.42 and 0.43, respectively) and cation content. On average, trees growing on acidic soils displayed 0.5 per thousand lower delta(13)C in both wood and leaf material than trees growing on neutral or calcareous soils. Our initial hypothesis of a strong negative relationship between delta(13)C and site water availability was not confirmed. In the study zone, neither wood nor leaf delta(13)C appeared to be a reliable bioindicator of spatial variations in water availability. Possible causes for the lack of a relationship are discussed. Our findings confirm, under natural conditions, the strong effect of soil fertility on water-use efficiency previously observed in experiments. This effect needs to be considered in isotopic studies involving different sites.

(in 1974), ii) herbicide application (glyphosate; in 1981), and iii) fertilization (P, K, Ca and Mg in 1982; N in 1982 and. A dendrochronological investigation was performed on 620 adult oaks from 60 to 200 years old, which were subjected to these treatments, alone or in combination. The results refer to basal area increment by comparison with control trees. The effect of drainage depended on the site type, the oak species and the age of the trees. Drainage had practically no effect in the Carex site. In the Molinia site, the effect was positive (+20%) for the young (≤ 110 years old) sessile oaks only. It became even depressive (-15%) for the old (> 110 years old) pedunculate oaks. The effect of weeding differed according to the site type, the age of the trees and the drainage modality. Whatever the drainage modality, the effect was depressive (-13%) for the young trees and nonsignificant for the old ones in the Carex site. There was a positive interaction between weeding and drainage in the Molinia site, in the old trees (+22%) as well as in the young ones (+17%), whereas weeding alone had a negative effect (-5%). The effect of fertilization was strongly beneficial (about +20%) in all cases, without any interaction of site type or drainage. However, the time dynamics of this effect was different according to the age of the trees: i) the mean effect was lower in the young trees (+15%), but it was still high when the trees were cored (1991); ii) it was higher in the old trees (+25%), but tended to vanish about 9 years after fertilizing. For