A dendroecological study was carried out on 196 sites distributed throughout the whole natural range of silver fir (Abiesalba Miller) in the Vosges mountains of northeastern France. At each site, six dominant trees were bored to the pith. Stand age varied, intentionally, from 40 to 180 years. All tree rings were measured and crossdated; data were then standardized with reference to the mean curve ring width vs. cambial age. The growth indices obtained in this way were studied (setting aside the cambial age) and revealed a great increase in mean vigour from 1830 to 1930–1940 (+70%) and a slight decrease from 1930–1940 to the present (−10%). Using meteorological data from Strasbourg (monthly precipitation and temperature data available from 1881) and a stepwise multiple linear regression, a climatic model was created that explains 79% of the variance. This amount included not only the monthly parameters of years y (year of ring formation) and y − 1 in the model, but also the parameters of years y − 2 toy − 6. Thus, the notion of structural autocorrelation loses much of its credibility in comparison with the notion of climatic aftereffects. The statistical validation of the model distinguishes a calibration period (1881–1960) and a verification period (1961–1983). The model reconstructs the long-term trends satisfactorily, as well as periodic severe growth declines of silver fir in 1917–1923, 1943–1951, and 1976–1983. These phenomena are mainly explained by climatic factors. The possible aggravating role of air pollution is put forward, in particular, the role of the CO2 increases during the last century.
SUMMARYSurveys of ground layer vegetation are a reliable tool for monitoring spatial and temporal variations of the forest environment. In 1991, 47 vegetation plots first sampled in 1972 in a forest of the Lorraine Plain, North-East France, were resampied. This beech-oak forest had both acidic and calcareous soils depending on the thickness of alluvial deposits above the calcareous bedrock. The mean number of species per sample increased from 32 to 39 during this period and tbe frequency of nitrophilic species increased throughout the forest. On acidic soils, acidophilic species increased in frequency, while on calcareous soils there were no systematic changes. Multivariate statistical analysis clearly distinguished two gradients in this set of vegetation samples: acidity and nitrogen availability of soils. Along the first gradient, a shift of the plots tovi'ards a more acidic state occurred during the past 19 years on acidic soils only. Along the second one, a strong eutrophication happened on both acidic and calcareous soils, indicating an enrichment in nitrogen of forest ecosystems. Possible causes of these changes are discussed, namely sylvicultural changes, aging of the stands and pollution. Atmospheric nitrogen inputs seem to be the most probable cause of eutrophication.
Summary — A dendroecological study was carried out in 2 forests in northeastern France with the aim of identifying and quantifying possible long-term trends in the radial growth of sessile oak (Quercus petraea (Matt) Liebl) and pedunculate oak (Q robur L). A total of 150 sites were selected to represent the ecological diversity of these forests. An index Cdwas used to correct annual ring width in order to compensate for the effect of different competition situations. The data were standardized with reference to the mean curve 'basal area increment vs cambial age'. The
RésuméLe dispositif retenu comprend 196 placettes réparties dans toute l'aire naturelle du sapin, de façon à couvrir toute la diversité des situations (âge, altitude, sol, telles 1870, 1893, 1916, 1922, 1934, 1948, 1956, 1961, 1976
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