Aim  To estimate the relative importance of climate and soil nutritional variables for predicting the distribution of Acer campestre (L.) in French forests. Location  France. Methods  We used presence/absence information for A. campestre in 3286 forest plots scattered all over France, coupled with climatic and edaphic data. More than 150 climatic variables (temperature, precipitation, solar radiation, evapotranspiration, water balance) were obtained using a digital elevation model (DEM) and a geographical information system (GIS). Six direct soil variables (pH, C/N ratio, base saturation rate, concentrations of calcium, magnesium and potassium) were available from EcoPlant, a phytoecological data base for French forests. Using a forward stepwise logistic regression technique, we derived two distinct predictive models for A. campestre; the first with climatic variables alone and the second with both climatic and edaphic variables. Results  The distribution of A. campestre was poorly modelled when including only climatic variables. The inclusion of edaphic variables significantly improved the quality of predictions for this species, allowing prediction of patches of presence/absence within the study region. Main conclusion  Soil nutritional variables may improve the performance of fine‐scale (grain) plant species distribution models.

Question: Can the distribution and abundance of Vaccinium myrtillus be reasonably predicted with soil nutritional and climatic factors? Location: Forests of France. Methods: We used Braun‐Blanquet abundance/dominance information for Vaccinium myrtillus on 2905 forest sites extracted from the phyto‐ecological database EcoPlant, to characterize the species ecological response to climatic and edaphic factors and to predict its cover/abundance at the national scale. The link between cover/abundance of the species and climatic (65 monthly and annual predictors concerning temperature, precipitation, radiation, potential evapotranspiration, water balance) and edaphic (two predictors: soil pH and C:N ratio) factors was investigated with proportional odds models. We evaluated the quality of our model with 9830 independent relevés extracted from Sophy, a large phytosociological database for France. Results: In France, Vaccinium myrtillus is at the southern limit of its European geographic range and three environmental factors (mean annual temperature, soil pH and C:N ratio) allow prediction of its distribution and abundance in forests with high success rates. The species reveals a preference for colder sites (especially mountains) and nutritionally poor soils (low pH and high C:N ratio). A predictive map of its geographic range reveals that the main potential habitats are mountains and northwestern France. The potential habitats with maximal expected abundance are the Vosges and the Massif central mountains, which are both acidic mountains. Conclusions: Complete niche models including climate and soil nutritional conditions allow an improvement of the spatial prediction of plant species abundance at a broad scale. The use of soil nutritional variables in distribution models further leads to an improvement in the prediction of plant species habitats within their geographical range.

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Aim On the basis of 2402 phytoecological relevés, with complete species lists, and real pH measurements resulting from chemical analyses of the top layer of forest soils, this paper compares quantitatively the ecological response of 46 herbaceous forest species along a pH gradient in two regions of northern France. LocationThe two regions investigated are oceanic north-western France (NW) and semicontinental north-eastern France (NE). MethodsFor each of the 46 species with more than 50 occurrences in both NW and NE regions, an ecological response curve was computed with simple logistic regression models, and two synthetic numerical values were derived: ecological optimum (OPT) and ecological amplitude (AMP). A comparison of the ecological behaviour of species present in both regions was performed in terms of shift in optimum and/or amplitude. ResultsAll 46 species did reveal a reaction to pH. Our main observation was the relative stability of the behaviour of most species with reference to pH conditions, which is consistent with results from some previous studies. Slight differences regarding the two synthetic parameters (OPT and AMP) were however observed between the NW and NE regions, probably due to a form of competitive release in neutral environments in the NW. Main conclusionsAmong the main possibilities that could explain a geographical shift in the ecological behaviour of herbaceous species, competitive effects are, we suggest, the most plausible explanation. In the light of former studies, it seems that further analyses of geographical shifts in the ecological behaviour of forest plant species over large areas are needed, such as for example over the European continent.Nomenclature Tutin et al . (2001).