Fourteen years of restoration and extensive year round grazing with free foraging horses and cattle and its effect particularly on dry species rich riverine levee grasslands
Sýkora, K.V. Stuiver, H.J. de Ronde, I. de Nijs, L.J.
In the Netherlands, nature management changed from conservation into active nature restoration. Restoration by reintroduction of natural processes including grazing is named "nature development". In 1992 the World Wildlife Fund announced the plan 'Living Rivers Plan'. One of the first nature development projects the 'Millingerwaard', started in 1991 by introduction of grazing by free foraging horses and cattle. One of the aims was the restoration of dry levee grasslands and in particular of the Medicagini-Avenetum which is threatened in the Netherlands. We studied the effect of nature development on vegetation, especially on dry levee grasslands (MedicaginiAvenetum, Bromo-Eryngietum) and on 'fluviatile species'. Permanent plots and repeated vegetation mapping was used to investigate changes. Classification was done by TWINSPAN. CCA and DCA were used to relate with environmental variables and to detect successional pathways. A succession scheme was drawn and changes in surface area of the different communities were calculated. After 14 years the surface area of the nitrophylous tall forb communities of the Galio-Urticetea strongly increased, while the Bromo-Eryngietum decreased. The Sedo-Cerastion ruderalized. On the levee nature development did not influence the total cover of Medicagini-Avenetum and the fluviatile species. Vegetation changes appear to be very dynamic showing both regressive and progressive succession. After 14 years of nature development, still no real improvement of the dry species rich Sedo-Cerastion grasslands occurred. This is most probably due to insufficient grazing intensity. Ruderalization of these grasslands can only be prevented if grazing intensity is sufficient to preserve short swards. Managers should either direct the herds or make sure that in the growing season the levees are sufficiently grazed because of an overall high grazing intensity in the area. Reintroduction of plant species might be necessary.