November 2005

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English summaries

    • DVD bestellen Negative effects of nature conservation on wintering geese in Natura 2000 areas
    • Nienhuis, J.
    • The Leekstermeer area (provinces of Drenthe and Groningen) is well known for its large numbers of wintering geese (White fronted goose, Anser albifrons). Since 1986 many agricultural fields changed into nature reserves. Recently the numbers of wintering geese have dropped significantly. Management changes within the reserves have caused a massive increase of Juncus effusus and Phalaris arundinacea. Consequently the infected fields were avoided by geese. The Leekstermeer area is not the only Dutch SPA where numbers of wintering herbivorous waterfowl have declined. Large areas of grasslands within the National Ecological Network are managed with low agricultural intensity. In this study fourteen such SPA’s were recorded. The experiences in the Leekstermeer area have pointed out that a significant drop in wintering geese may be expected after the introduction of extensive grassland management. This may have serious consequences for the management of other areas protected by the EU Birds Directive.
    • DVD bestellen Carabid beetles in changing roadside verges in the Veluwe
    • Noordijk, J., H.J.W. Vermeulen & Th. Heijerman
    • We compared the carabid beetles of two roadside verges on pleistocene sand in the Veluwe in 1989 and 2003. Due to natural succession, accelerated by nitrogen deposition, grasses and pine trees are becoming more abundant in these roadside verges. Specialist carabid beetles from drift sand areas are the first victims of this process. Species of heathlands remained present, while forest species became more abundant. To maintain ecological interesting roadside verges, management is necessary. Characteristic carabid beetles from the Veluwe will benefit from the removal of trees and the creation of sandy areas in the verges.
    • DVD bestellen Recovery of insect biodiversity in the ‘Gelderse Poort’, an example of floodplain restoration
    • Kurstjens, G., P. Calle & B. Peters
    • The effects of large-scale floodplain restoration in the Gelderse Poort on dragonflies (Odonata), butterflies (Lepidoptera) and grasshoppers and crickets (Orthoptera) are discussed. Since 1990 more than 800 hectares of agricultural floodplain area are transformed into new nature areas in which natural processes such as flooding, morfodynamics, grazing and spontaneous vegetation development are reactivated. Clay mining on an economic basis (brick industry) is used as an instrument to improve the water retention capacity of the floodplain. New marsh habitats are a very welcome spin-off. The Gelderse Poort project is not restricted to the present floodplains. Also former floodplains (land behind dikes) with old riverbeds mainly consisting of (reed) marshes are involved. Nowadays 40 species of dragonfly live in the area. Six Red List species appeared to occur with considerable populations. Compared with data from recent decades the species richness increased clearly, both in the present floodplain and in the marshes of the former floodplain. This increase is boosted by various factors: the improvement of the river water quality, the climate change (colonisation by Mediterranean species) and habitat recovery by nature restoration (side channels, new marshes, alluvial forest, vegetation structure created by beavers and large herbivores). The situation for butterflies is rather different. In the floodplain the species richness recovered slightly since 1990. Three threatened species profited from the increased flora diversity and improved landscape structure. Regular inundation is a dominant factor with negative effects on the survival of hibernating butterfly species in the floodplain. In the former floodplain behind the dikes the number of butterfly species decreased by 25% as compared to historical data. Return of most disappeared species in the area is not likely because source populations are extinct in and around The Netherlands. The number of species of grasshoppers and crickets in the Gelderse Poort is more or less stable. Recently two Red List species colonised the area and some southern species expand their ranges northwards due to global warming. The most striking result of nature development in the floodplain is the huge increase of biomass of grasshoppers in the natural grasslands. It is concluded that dragonflies in particular are proper indicators of floodplain restoration effects. The results of the nature development in the Gelderse Poort are very promising.