March 2005

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English summaries

    • DVD bestellen Uncertain future for Bialowieza Primeval Forest
    • Verhart, F., H. Smeenge & B.L.M. van der Linden
    • The Polish and Belarussian strict nature reserves of Bialowieza Primeval Forest are recognised as unique woodlands within the lowland of Europe. Commercially exploited parts of Bialowieza, in which an ecological network of "old growth"-stands is present, do surround these reserves. The "old growths" possess natural qualities comparable to the strict reserved parts. However, due to internal and international political interference and deeply rooted conflicts on managing the woodland as a single area, protected or formerly protected stands are being cut down under pretext of controlling outbreaks of Bark beetle. This is a major threat for the preservation of this unparalleled World Heritage Site and World Biosphere Reserve. A primary solution can be found in putting a ban on cutting trees in "old growths". Transboundary cooperation aimed at an ecological coherence of forest protection, forest and hydrology management and development of ecotourism must be persisted and intensified.
    • DVD bestellen Establishment of hardwood species in the Beuningen riverine floodplain
    • Kuiters, A.T. & S.J. Vreugdenhil
    • In nature restoration sites along Dutch rivers, the establishment and growth of shrub, softwood and hardwood species is a natural process which is allowed to proceed at certain preconditions. A sufficient flow capacity of river water must be guaranteed. We studied the impact of flooding and ungulate grazing with cattle and horses in the riverine floodplain of Beuningen on the establishment of woody species. Grazing pressure amounted to ca one grazer per 2 ha. A comparison of aerial photographs from 1997 and 2001 revealed that woody vegetation cover had increased with 15% during a 4-year period. Besides softwood species with Salix alba as most common species, cover by hardwood species such as Crataegus monogyna and Quercus robur had also increased. Hardwood species were not found at places with a flooding period beyond 100 days a year. For oak samplings this was maximal 35 days a year. Year-round visual observation revealed that even in this relatively small area, grazing pressure of cattle and horses was rather heterogeneous, with grazing pressure differing by a factor 2.5. It is expected that hardwood species such as Quercus robur, Fraxinus excelsior and Ulmus spec. will profit from a further expansion of thorny shrubs such as Crataegus monogyna, that can act as ‘nurse-species’. It is questioned if grazers, eventually complemented wit Red deer in the near future, will be able to keep riverine floodplains along Dutch rivers sufficiently open. If not, an additional management measure such as cyclic rejuvenation by periodically cutting of floodplain woodland will become inevitable. This can be seen as compensation for a lack of natural disturbance, because Dutch rivers can no longer meander in a free way.
    • DVD bestellen Enhancing water storage capacity while conserving river corridor species
    • Eck, W.H.J.M, J.P.M. Lennsen & H. de Kroon
    • Climate changes may lead to higher water discharges of rivers. To reduce the risk of floods, plans are made to increase the water storage capacity of river floodplains by lowering the riverbank. These measures will increase frequency and duration of flooding events and may thus threaten river corridor species that are now restricted to high-elevated river dunes. A number of field and greenhouse experiments demonstrated that species’ lower distribution limits are directly determined by their tolerance to summer floods. Moreover, these limits remain relatively stable after prolonged periods without summer floods. Seed limitation, sand deposition by winter floods and competition with flood tolerant species prevent descend of flood-intolerant species to lower elevations. By excavating river banks to enhance water storage capacity, it is thus important to conserve high-elevated elements in the river landscape, since many rare river corridor species are sensitive to flooding.
    • DVD bestellen The Black grouse on the Sallandse Heuvelrug: prolonged struggle for the preservation of the last surviving population in The Netherlands
    • Bruijn, O. de, P.H.A.M. Dirks, P.G.A. ten Den, T. Klomphaar & H.G. Veerbeek
    • The Black grouse is a characteristic bird of the edges of heaths and moors where these adjoin grassland and open woodland. The recent serious decrease of the Black grouse in range and numbers in Western-Europe can be attributed to fragmentation and degradation of the breeding habitat (increased abundance of grasses on heaths and the drying out of moors), more efficient and intensive agricultural use of the adjoining farmland, as well as the disturbance caused by increased recreation pressure and the predatory activities of Foxes (Vulpes vulpes) and Goshawks (Accipiter gentilis). In 2004, only fifteen males were counted at the last remaining site in the Netherlands, the ‘Sallandse Heuvelrug’ (province of Overijssel). Besides the factors already mentioned, climatic warming with wetter winters and springs has had a negative effect on the Black grouse which is adapted to cold, snowy winters and warm, dry springs. Presently, high chick mortality is a key factor in the decline as a result of a lack of food (insects) and poor weather conditions.In 1991, a Black Grouse Conservation Plan was launched by the Dutch government. In line with this plan, conservation organisations (Natuurmonumenten and Staatsbosbeheer) are structurally improving the grouse’s habitat on the Sallandse Heuvelrug. This includes the stimulation of heather regeneration, deforestation and the modification of agricultural practices in the surrounding farmland. Active management (sod-cutting, mowing, woodcutting) is leading to a mosaic heathland with long and short heathers (Calluna vulgaris), patches of Vaccinium vitis-idaea, local Juniperus communis shrubs, and semi-open woodland with Vaccinium myrtillus. Besides this patchwork-type of heathland management, sheep grazing has been stopped, some 300 ha of forest has been felled, and gradual transition zones from heath to woodland are being created. In addition, the predatory losses are kept low by shooting Foxes, and recreation zoning measures have been put in place to restore quiet areas. Unfortunately, so far, the Black Grouse has not seen an increase in numbers from this intensive habitat management. Nevertheless, a breeding population has survived on the Sallandse Heuvelrug, and habitat-use observations show that the grouse are reacting positively to the measures undertaken. Moreover, positive population trends in other characteristic (insectivorous) species of heathland communities are encouraging, in particular Nightjar (Caprimulgus europaeus), Stonechat (Saxicola rubicola), Woodlark (Lulula arborea) as well as the Sand lizard (Lacerta agilis). Over the last years, Natuurmonumenten has reinstated some fields of traditional crops (oats, spurry) and Staatsbosbeheer is acquiring adjoining farmland for future marginal grassland use for the benefit of the Black grouse. Eventually, repopulation of this area with lowland Black grouse (bred in captivity or obtained from abroad) may be an appropriate option once the conditions that led to the population decline have been sufficiently resolved.
    • DVD bestellen Old coppices on the Veluwe need a new management
    • The occurrence of ancient woodland, in fact very old coppices, occurring in the Veluwe region is described. By extensive mapping we have shown the real extent of these woodlandsites is ca.11,000 hectares. Surprisingly, in some of these woodlands extraordinarily large oak coppice stools of very high age are present. Moreover, we discovered coppiced beeches, which was less expected. The Common beech woodland, managed in the past by the commoners, is shown to be originally coppice, including singled trees. The authors give their view on the management of this considerable and important area of Oak-beech woodland, in order to preserve it for the future. We propose a primary Ancient Woodland Infrastructure, including connection zones, to counteract the ongoing upsplitting of the remaining old woods, introduction of autochthonous trees and shrubs and an adaptation of the hunting and the grazing management. Besides, we propose to designate areas where autochthonous oak, beech, crabapple and holly populations will be safeguarded as important gene pools and cultural monuments.
    • DVD bestellen The Atlantic croaker (Micropogonias undulatus L.), a new fish species in The Netherlands
    • Dekker, W., N. Daan, H.J.L. Heessen & W. van der Heij
    • The first observations of Atlantic croakers (Micropogonias undulatus L.) from Dutch waters are described: one specimen caught in the Wadden Sea in oktober 2003 and two young-of-the-year caught in October 2004 in the North Sea Canal (North-Holland). Atlantic croakers, Percids native in the Western Atlantic and recently described from Belgian waters, might have been introduced in ballast water tanks by ship traffic. Since only young-of-the-year have been caught, not showing any sign of growth retardation related to stressing transport in ballast tanks, we speculate that our specimens are at least first offspring of the actual introduction.