The last century about 60% of the coastal dunes in Flanders diminish- ed and what remained is very much fragmented. Active landscape deter- mining processes (e.g. blowouts and parabola dune formation) only occur at the larger dune reserves in De Panne en Oostduinkerke. The withdrawal of the traditional grazing by domestic livestock caused growing thick by dune shrub (mainly Sea Buckthorn Hippophae rhamnoides) in almost all habitats. To have knowledge of the habitat preference of grasshoppers (Saltatoria) in the dunes, we walk a transect (from the sea to the inland polders) in the two complexes of De Panne and Oostduinkerke. It is our aim that the information about the habitat preference of endangered invertebrates (in relation with management regimes) should be incorporated into management plans of dune reserves to optimise insect conservation, this in addition to a botanical framed conservation management. Along those two transects we distinguished five major habitats - sandy dunes, dune shrubs, wet grasslands, dry grasslands and dune forest by vegetation features. Grasshoppers were sampled by net sweeping (grasslands), umbrella beating (threes) and visual and auditive records. A total of eighteen species (55% of present known species in Flanders) were caught during the sample sessions. Twelve species were caught in the yearly mown dune slacks (wet grasslands) and ten species in the pioneers dune slacks with scarce vegetation (sandy dunes) and in the rough dry grasslands. Conocephalus dorsalis, Tetrix subulata and Chorthippus parallelus are restricted to the 'wet grasslands' and to the 'dune shrubs' are Leptophyes punctatissima and Meconema thalassinum. Tetrix ceperoi only occurs in the 'sandy dunes'. Myrmeleotettix maculates and Oedipoda caerulescens occur both in 'sandy dunes' and in 'dry grasslands'. The latter is also the habitat of Stenobothrus stigmaticus, Platycleis albopunctata, Tetrix undulata, Chorthippus brunneus and C. biguttulus Chorthippus albomarginatus and Conocephalus discolor were found in as well dry as wet grasslands. The latter needed a rough vegetation pattem. From Tettigonia viridissima, Pholidoptera griseoaptera and Chorthippus mollis were not enough data available. Coastal dunes are of special importance for the large populations of Tetrix ceperoi, Oedipoda caerulescens, Stenobothrus stigmaticus (three endangered), Platycleis albopunctata and Chorthippus albomarginatus, two rare species in Flanders (DECLEER et af., 1989). The situation of S. stigmaticus is extremely critical since there are only two populations in Flanders. The maintenance of S. stigmaticus can only be obtained by conserving enough, short grazed patches in the dune area where the species occurs (Oostvoorduinen). At this moment the area is still private property, as a consequence no integral and extensive grazing management can be introduced. However, this is the only way to maintain and increase the surface of short grassland with sandy patches, the habitat of this endangered species. |
