Geostatistical interpolation of abiotic site conditions in the Netherlands: A method for reference mapping

Actual and historical data were interpolated to illustrate the actual and historical abiotic situations in the Netherlands, resulting in grid maps of 250×250 m² and 1000×1000 m² resolution, respectively. Prior to interpolation, data were selected from two time periods (1930 to 1970 and 1991 to 1997) and stratified on the basis of the dominant soil types underlying the vegetation records. Interpolation was done through local ordinary block kriging. This method allows us to produce unbiased estimates with their respective estimation errors at different geographical scales.

The resulting maps were compared to other available information and discrepancies analysed. Overall, our results agree with other abiotic maps and expert knowledge. There are, however, inaccuracies in the interpolation results, caused mainly by sampling (design), stratification and the assumptions chosen for the interpolation. Inferences about the results and especially comparison of abiotic site conditions in time will require detailed analysis and, if necessary, corrections of these inaccuracies. We suggest further detailed examination of the maps presented and correction of obvious errors in the maps prior to their application for reference.