In geological settings where the water table is a subdued replica of the ground surface, cokriging can be used to estimate the water table elevation at unsampled locations on the basis of values of water table elevation and ground surface elevation measured at wells and at points along flowing streams. The ground surface elevation at the estimation point must also be determined. In the proposed method, separate models are generated for the spatial variability of the water table and ground surface elevation and for the dependence between these variables. After the models have been validated, cokriging or minimum variance unbiased estimation is used to obtain the estimated water table elevations and their estimation variances. For the Pits and Trenches area near Oak Ridge National Laboratory, water table estimations along a linear section, both with and without the inclusion of ground surface elevation as a statistical predictor, illustrate the advantages of the cokriging model.

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-The present study re-examines the influence of ecological conditions on the health of silver fir (Abies alba) measured in 1989, during the so-called forest decline crisis, in the sandstone portion of the Vosges mountains, on the basis of an assessment of almost 3000 forest management units (10-20 ha each). Relationships between defoliation and needle yellowing (related to Mg deficiency) and environmental factors were analysed with contingency tables and modelled using discriminant functions. The results confirmed the predominant influence of altitude and stand age; these two factors explain 70% of the spatial variability of defoliation and 64% of that of yellowing. In addition, a database composed of 178 soil analytical profiles was analysed in relation to the geographic database. The commonly used variable "altitude" appeared to combine the influence of several related variables which are crucial for the biological functioning of the tree: especially the plant available water holding capacity and chemical characteristics were negatively correlated with elevation in the study area. This ecological feature is likely to be common to a number of mid-elevation mountain range in Europe and was often neglected in the earlier studies on forest decline. forest decline / Abies alba / GIS / spatial analysis / discriminant analysis / Vosges mountains Résumé -Relations entre les conditions écologiques et le dépérissement du sapin dans les Vosges gréseuses (France).Ce travail réexamine l'influence des conditions écologiques sur le dépérissement du sapin, mesuré lors de la crise du dépérissement forestier dans les Vosges, sur la base d'une notation exhaustive de 3 000 parcelles forestières (10-20 ha) gérées par l'Office National des Forêts dans les Vosges gréseuses. Les relations entre défoliation et jaunissement des aiguilles (généralement dû à une carence en Mg) et les conditions environnementales moyennes de chaque parcelle ont été étudiées par des tableaux de contingence, et modélisées en utilisant une analyse discriminante. L'altitude et l'âge des peuplements expliquent respectivement 70 % de la défoliation et 64 % du jaunissement. Le paramètre « altitude » combine de nombreux facteurs influençant le fonctionnement physiologique de l'arbre. En utilisant une base de données de 178 profils pédologiques, nous montrons que l'altitude est négativement corrélée à la réserve utile des sols et au taux de saturation, indépendamment du type de grès. Ce type de distribution est probablement assez banale dans un certain nombre de moyennes montagnes européennes, et forme un biais souvent négligé dans les études de dépérissement. dépérissement forestier / Abies alba / SIG / analyse spatiale / analyse discriminante / Vosges Ann. For. Sci. 59 (2002) [265][266][267][268][269][270][271][272][273] 265

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