Feasibility of target communities in a Dutch brook valley system

As a reaction to the ongoing deterioration of nature conservation interest in The Netherlands, an offensive nature strategy was formulated in the 1990 Nature Policy Plan. In this Plan, target communities and target plant species are mentioned. For the ’Drentse A brook valley system’, target communities were assessed by the Province of Drenthe. In the present study, a model is described that predicts the number of target plant species for four seminatural target communities, namely; species-rich meadow, heathland, arable field and species-rich woodland. Information is used on the present and past occurrence of target plant species in the study area. An estimate is made for the probability of germination from the seed bank and for the probability of seed dispersal for each of the four target communities. The model predicts a large deficit between the number of predicted plant species and a completely developed target community. Only half the target plant species can be expected at a maximum (for species-rich meadow). For heathland, 38% of the target plant species can be expected, while for speciesrich woodland and arable field not more than 16% and, respectively, 8% of the target species are predicted to occur. Therefore, if nature policy in The Netherlands aims at completely developed target communities, there is an evident need for extra measures such as active introduction of species.