Predicting soil classes with parameters derived from relief and geologic materials in a sandstone region of the Vosges mountains (Northeastern France)

The present study involves the possibility of using geology and relief to m ap soil classes. We initially focused on two small catchments considered as representative of a 6000-ha forested area overlying a sandstone bed. The c atchments differed in the stratigraphic sequence of sandstones, i.e., rich or poor in weatherable minerals. In one, the depleted bedrock was downstrea m and the rich was upstream, and the converse obtained for the second. Rela tionships between soil classes and environmental factors were modeled using two discriminant functions corresponding to the two types of stratigraphic sequences found in the catchments. More than 70% of the soil class distrib ution in small catchments can be explained by the nature of the substratum and attributes derived from a digital elevation model (DEM). These relation ships were then applied to a larger region. An automatic catchment delineat ion was first carried out with the DEM and was then combined with geologic maps. The choice between the two discriminant functions was based on the st ratigraphic sequences in each catchment. Predicted soil classes were compar ed to soil classes conventionally mapped in 1978 at the scale of 1:100,000. The results show that the model reproduced the soil map over 55% of the ar ea studied. Disagreements were due primarily to the existence of superficia l deposits not mentioned on the geologic maps and to an altitude effect tha t is not sufficiently considered in the study of small catchments. (C) 1999 Elsevier Science B.V. All rights reserved.