The distribution of Senecio jacobaea L. and Tyria jacobaeae L. in relation to soil properties

The distribution of S. jacobaea in The Netherlands is compared with local water-table depth, degree of drainage and calcium content. As surface units, hour squares (5.25 km x 5.25 km) are used. Water-table depth accounts for a greater part of the variance in the distribution of Ragwort than soil drainage. The variance accounted for by water-table depth and calcium content is of the same order. In the category of soils which have a low water level and are calcareous at the same time. Ragwort is very frequent (in 96 % of the squares). A significant relation of the distribution of the main consumer of Ragwort, T. jacobaeae, to soil drainage, as was found in England and Wales, could not be shown for The Netherlands. However, indications are given that egg distribution of T. jacobaeae is related to the area and density of Ragwort populations.