S I." M M A R YComparisons are made between ring-width response functions relating to precipitation and temperature in 72 Quercus populations {Q. afares Pomel, Q. canariensisV^xWd., Q. pubescens Willd. and Q. robur L.) situated in the north and south of the western Mediterranean region. A multivariate procedure applied to the whole set of response functions allows a distinction to be made of three types of response function according to the species considered. Analogies and differences between coded response functions are revealed by the calculation of a mean response, firstly for each species and for the genus, secondly for the groups of response functions derived from the multivariate analysis. For all the populations, and hence for the entire Quercus genus, a direct response to summer precipitation and an inverse response to temperature, especially minimum temperature, are obtained for the summer period. For the other seasons, each species is characterized by a particular behaviour conditioned by the characteristics, of the habitat.
'his paper is concerned with the \alue ot the ecological lntormation prin lded by response functions. Two Questions are considered. The first deals with the spatial reproducibility of response functions ctepending on the ''•^e population and the location of the meteorological station that yielded the climatic data. The second concerns the temporal stability of the response function. The climate-ring-width relationships are calculated for six Populations of Pinus silvcstris (L.). TweK e meteorcilogical stations are in\'olved in this calculation, over the period "•'0-1980, di\ided in live seciuences of SO years. Analogies and difterences between response functions are "ivestigated using multi-dimensional anaKsis (principal component analysis and cluster analysis).Spatial analysis reveals that the climate-ring-w idth relationship mainly depends on the population habitat. Thê TOporal analysis shows that instability is linked with the evolution of the hat^itat, more especially with the '-'^Pansion of the forest cover.
Effet des facteurs stationnels sur la croissance radiale et la réponse du pin d'Alep au climat dans le massif de l'Ouarsenis, Algérie Photo 1. Vue d'ensemble de la zone culminante de l'Ouarsenis où de vastes pinèdes se développent sur substrat calcaire. Photo M. Sarmoum.
Tree-ring series from living trees near the timberline or timbers buried in the surroundings are exceptionally valuable both for climate reconstruction and investigations of the consequences of climate change to ecosystems.This paper is a critical assessment of the past and potential contributions of dendroecology and dendroclimatology in mountain environments. Problems addressed are the spatial variability of both climate and tree sites, the temporal variability of ecological growth conditions and the reconstruction of signals other than high frequency ones. A synoptic approach appears to be the only way to take into account both the spatial and temporal variability of tree-growth, allowing for a better comparison of spatial climatological patterns with spatial growth patterns.
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