Habitat and vegetation response prediction for meadows and fens. Application of SMART-MOVE on a regional scale

Abstract

To assess the impact of integrated management plans on brook valley ecosystems in the catchment area of the river Dommel, an integrated landscape ecological model is developed. Within this integrated model the Nature Planner (developed at the national institute of the public health and the environment (RIVM)) is used to predict effects for meadow and fen vegetation. Because the Nature Planner was developed for use at the National scale, it could not directly be applied for the regional scale of the Dommel catchment. Therefore the fundament of the nature planner, the models SMART2 developed at the DLO-Staring Centre) and MOVE (developed at the RIVM), were rewritten for application within the GIS ArcInfo to implement the flexibility of a GIS. Vegetation response prediction is carried out with the model MOVE, using three environmental variables: acidity, nutrient availability and wetness of a site. All three variables are based upon Ellenberg indication values, which have to be calibrated to measurable environmental habitat conditions. Calibration of Ellenberg indication values for acidity and wetness was already carried out. Calibration of Ellenberg-N indication values to measured nutrient availability of the soil was still necessary. Therefore a comprehensive field experiment in the catchment areas of the Dommel and the Zwarte Beek (B) was carried out. This experiment resulted in a significant relationship between Ellenberg-N indication values and net annual N-mineralization. The variables N-mineralization and acidity are simulated with the model SMART2. The variable wetness is implemented as the mean spring groundwater level, simulated with a hydrological model of the catchment area by Pieterse et al (1998a, 1998b). SMART2 simulations are compared with measurements in the Dommel catchment. Simulations of acidity are comparable with measured acidity. N-mineralization simulations do not match with field observations. Moreover, these simulations do not differentiate between various sites, although these sites have different soil properties and different hydrological regimes. The MOVE variable Ellenberg-N is therefore excluded from the MOVE equations. Because the multiple regression equations of MOVE cannot be altered, the optimum N for each plant species is used instead. MOVE simulations were carried out for the catchment area of the river Dommel. Simulations are in agreement with expectations of potentials for nature development, based upon fieldwork. The simulations show that in the larger part of the catchment, the probability of occurrence of species-rich grasslands and fens is very low for the current hydrological situation. At some locations however, a relative high probability of occurrence for Calthion palustris and Junco-Molinion is simulated. Because habitat conditions in the Dommel catchment are more likely to be eutrophic than oligothropic, the probability of occurrence of oligothrophic and mesothrophic vegetation types (Junco-Molinion, Caricion nigrae and Calthion palustris) is overestimated. From inventories of the occurrence of grasslands and fens in this catchment, it is concluded that hardly any of these vegetation types, and especially the species-rich types, are left. Therefore a validation of model simulations is not carried out.