September 2006

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English summaries

    • DVD bestellen The Weatherfish in The Netherlands
    • Eekelen, R. van & A.H. van den Berg
    • The dependence on dense water vegetation makes Weatherfish (Misgurnus fossilis) vulnerable to intensive ditch cleaning when all vegetation is removed. Because the largest part of the population of Weatherfishes is distributed outside nature conservation areas (e.g. Natura 2000) the existence of this species depends largely on patches of vegetation which are accidentally left after ditch cleaning. To guarantee its present distribution a number of measures is proposed. An estimated length of 1000 -1400 meters of ditch is required for a sustainable population. Annually no more than one 6th part of the total length should be cleaned to ensure sufficient habitat.
    • DVD bestellen Remarkable bryological developments on coarse dead wood on the southeast Veluwe (central Netherlands);
    • Bijlsma, R.J. & A.J.M. ten Hoedt
    • After the discovery of the supposedly extinct Riccardia latifrons on dead wood of beech on the southeast Veluwe in 2000, this liverwort turned out to be rather frequent on decorticated logs of Scots pine in the same area (more than 60 records). Riccardia occurs predominantly on pine logs with diameter 15-60 cm in open former oak coppice with Scots pine planted between 1880 and 1920 and a herb layer of bilberry (Vaccinium myrtillus). Frequent accompanying species are Tetraphis pellucida, Lepidozia reptans, Cephalozia bicuspidata, Campylopus flexuosus, Hypnum jutlandicum and Lophocolea heterophylla. The rare Nowellia curvifolia was found in the same habitat (more than 30 records) as well as Calypogeia neesiana and Cephalozia catenulata, both new to The Netherlands. This development is a result of prolonged non-intervention management in a more or less continuously forested area and is probably reinforced by a high mean annual gross (>850 mm) and net precipitation (>320 mm). Another development is that several liverworts of stem bases and mineral soil on wooded earth banks and in (former) heathlands colonize rotting pine logs succesfully, such as Calypogeia muelleriana, Cephalozia bicuspidata and Lepidozia reptans. Moreover, these species produce perianths (related to sexual reproduction) much more often on decaying wood than on soil. Other rare species, known only from terrestrial habitats in the Netherlands appear on pine logs as well such as Calypogeia azurea, C. integristipula, Cephalozia lunulifolia and Odontoschisma denudatum. Decaying wood thus appears not only a habitat for strictly epixylic liverworts but also an optimal habitat for several bryophytes up to now confined to mineral soil and stem bases due to the absence of dead wood. Both groups depend on decaying wood for sexual reproduction and subsequent long-distance dispersal. The range extension of several northerly or montane bryophytes in the Netherlands is remarkable in the light of climate change of which southern species benefit the most.
    • DVD bestellen ‘Wait and see’ pays off with Ragwort problem
    • Bezemer, T.M., W.H. van der Putten & F. Rienks
    • Poisonous Ragwort (Jacobaea vulgaris) dominating the vegetation is a common problem in new nature areas in The Netherlands. Unnoticed by the cattle, it causes intoxication via the hay. Large-scale extermination is not strictly necessary though. Leaving Ragwort plagues for about four years proved to be able to cause a natural decline of the population, as recent ecological research shows. Soil fungi appear to work against their former ‘partners’ and bring about soil exhaustion. Also, sowing herbaceous plants resulting in a denser vegetation keeps the killer herb almost out. In the end, Ragwort is just a normal phenomenon in an early stage of nature development and as the vegetation develops the problem fades away.
    • DVD bestellen The effects of a provincial road on ground beetles
    • Prins, D., M. de Jonge, J. Noordijk & H.J.W. Vermeulen
    • Roads are often a barrier for the fauna in adjacent nature areas. In this research we studied the barrier effects of a provincial road on ground beetles in the heathland area Mantingerveld. The Mantingerveld is a nature restoration area in the province of Drenthe, The Netherlands. During two months in spring a mark-recapture experiment was conducted to determine the direction of movement of two species and road kill on the provincial road was collected to determine which species crossed the road. The mark-recapture test was carried out using an enclosure that stretched over the road. Within the exclosure individuals of the carabid species Poecilus versicolor (1188 induividuals) and Agonum sexpunctatum (113 individuals) were released on one side of the road. The beetles released in the exclosure showed a strong directional preference to move alongside the road, whereas the movement of the beetles in the control exclosure showed no selective direction of movement. Only 22 individuals of P. versicolor (1.85 %) were caught on the other side of the road, but none of the released individuals of A. sexpunctatum crossed the road. Road kill included only individuals of P. versicolor, and although there are many stenotopic heathland species living in the area close to the road, only the relatively large heathland species Carabus arvensis was found killed by traffic. This might indicate that stenotopic heathland species are reluctant to move onto the asphalt. The tendency of the released carabid beetles to move alongside the road and in ditches can be used to guide animals to suitable habitats using roadside verges. To decrease the barrier effects of the provincial road and to connect different areas in the Mantingerveld area for other species as well, a wildlife overpass with guidance towards it will probably function as a palliative to the local fauna.