Factors affecting the vegetation of ditch banks in peat areas in the western Netherlands.
The effects of various environmental factors on the ditch bank vegetation in peat areas in the western Netherlands were studied to find the best management strategy for conserving the flora of ditch banks. The effects of these factors on three different indices of floristic richness and on individual plant species were assessed by spatial comparisons of sampling plots using analysis of variance and matched pairs analysis. The floristic richness of the banks was higher on south-facing than on north-facing banks, and on steep south-facing than on gentle south-facing banks. Higher soil pH, high ditch water table (especially at north-facing banks), low grazing intensity and a low nitrogen supply on the adjacent fields (especially at fertilization rates of less than 200 kg nitrogen ha-1 year-1) also favoured floristic richness. Type of peat soil, amount of manure and slurry applied to the fields, and phosphorus and potassium contents of the bank soil had no significant effects on floristic richness. To maintain the species richness of the vegetation, it is recommended that: (i) ditch banks are kept free of fertilizer and are protected from grazing by livestock; (ii) ditch water levels are kept high; (iii) that acidification is prevented; and (iv) south-facing banks are kept steep.