Geographic structure and potential ecological factors in Belgium

The available potential ecological factors have been scored in the form of presence/absence in Universal Transverse Mercator (UTM) squares in Belgium. A correspondence analysis shows a strong underlying gradient in the data set which induces an extraordinary horseshoe effect. This gradient follows closely the altitude component. Applying the k-means clustering method on UTM squares produced geographically compact groups which are largely hierarchically nested. This indicates strong regional trends in the ecological data set. As homogeneous groups may also be artefacts created by the clustering algorithms on a continuous gradient, the relevance of the borders between homogeneous areas is tested. In general, k-means borders correspond to the main breaking lines between adjacent UTM squares. They can be referred to as natural borders. -Authors