Mapping and monitoring issues of a forest soil network in Southern Belgium.

Soil monitoring has become a rising concern during last decade in Europe. A Forest Soil Survey (FSS) is being implemented in Southern Belgium as a component of a forest observation and monitoring programme. An analysis of the monitoring network has been performed at mid-term of the first investigation stage in order to assess current soil conditions and the temporal evolution that can be detected in the future. The fertility status and the determinism of major and trace elements in forest soils have been investigated at regional scale through uni- and multivariate statistical analyses of the 410 soil samples of the network. A performance analysis of the network has been realized regardings the capacity to detect evolution of soil parameters. The first results show a moderate to strong variability according to the variable considered. High levels of variability were attributed to the presence of carbonated parent material in a distribution largely dominated by detritic terrigeneous rocks. The total contents in forest soils are mainly driven by pedo-geochemical background. The FSS allowed detailed mapping because there are clear convergences between spatial distributions of most of the elements and lithology or small natural regions. The levels of minimum detectable differences (MDD) that can be expected seem only compatible with the monitoring of soil acidification and changes in carbon stocks on the long-term. Future prospects should focus on the improvement of the MDD assessment.