November 2011

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English summaries

    • pdf downloaden Towards core areas for meadow birds, what will be the outcome?
    • Th.C.P. Melman, H. Sierdsema, W.A. Teunissen & A.G.M. Schotman
    • Dutch governmental organisations are considering to preserve meadow birds within core areas. The past thirty years of meadow bird policy the decline did not stop. The idea is that concentrating efforts on a limited area is more effective than dilute efforts over a large area. This article explores the possible impact of core areas, to bring about discussion. The Black-tailed godwit is used as a guide species. Selecting the areas with the highest densities covering 50% of the Black-tailed godwit population comprises approximately 125,000 hectares of grassland: the 50%-godwit area. This is still far more than the currently managed area of  ca 57.000 ha, therefore it is likely that core areas will cover only a limited portion of the population. In almost all of these areas the trend appears to be negative. Obviously, at the moment the current circumstances in the ‘top’ areas are insufficient for stable numbers. Next, of the other meadow bird species only a modest proportion (10-20%) lives inside the 50%-godwit area. So, combined conservation of all these species needs specific attention. Apart from the high-quality cores with proper drainage and management, attention is needed for the quality of the surrounding landscape. In this bufferzone openness and absence of disturbance have to be taken care of. This urges for serious regional policy.

    • pdf downloaden Changes in stream macro-invertebrate communities due to water quality improvements
    • J.P.M. Lenssen, A.G.M. Klutman, R.C. Nijboer & G. Boedeltje
    • The last decades have shown a tremendous decrease of organic and nutrient load in streams in The Netherlands. During the last 23 years, macro invertebrates have been monitored in a consistent manner in most of the streams in the Dutch region Oost-Gelderland. The data allow us to assess the effect of improved water quality on macro invertebrate communities during the last 23 years.

      This effect strongly depends on the stream type. In highly regulated streams, i.e. canalized, enlarged in profile and barraged, we noticed a shift from species with high tolerance against low oxygen concentrations in the water towards species with a slightly higher oxygen demand. However, the resulting community was still dominated by limnophilic species.

      Different shifts were noticed in unregulated streams, where stream velocities tend to be higher and morphological variation offers a wide variety of substrates. Here we noticed a clear shift towards species with high oxygen demand. Moreover, the number of rare species (indicative of undisturbed stream environments) also significantly increased in unregulated waters, whereas no increase occurred in regulated waters.

      These results clearly demonstrate the interaction between water quality and stream morphology and hydrology. Improvement of water quality is not sufficient if stream hydrology and morphology is not restored. On the other hand, natural stream communities are highly susceptible for changes in water quality.

    • pdf downloaden Decreased nitrogen deposition is not sufficient to restore dry acid grasslands
    • E. Dorland, R. Bobbink, M.B. Soons & S.L.F. Rotthier
    • Species richness of dry acid grasslands (Violion caninae) in western Europe is still threatened by atmospheric nitrogen (N) deposition. Analyses of a large set of vegetation relevees, covering a period of almost 70 years, indicated that species number was most strongly correlated to soil pH (positive relation) and accumulated N-deposition (negative relation). These results were confirmed by our correlative survey of 153 dry acid grasslands in ten countries in which species richness significantly decreased with increasing N-deposition. Our results were in line with the European critical load set for these grasslands. Especially herbs declined in number as a result of increasing N-deposition, whereas the proportion of grass species increased. The recent reduction of N-deposition is not sufficient to restore former species richness of dry acid grasslands, due to accumulation of N in the soil as well as soil acidification. To restore these ecosystems successfully it is therefore necessary to further decrease of N-deposition, to remove excess N and to restore soil pH. When refuge populations of target species are absent from the area, reintroduction of diaspores will be required.

    • pdf downloaden De Levende Natuur 110 years: from Heimans and Thijsse to DVD’s
    • J.P. Bakker, I.C. Knevel & H.J. van der Windt
    • The journal De Levende Natuur was established in 1896. Initially it published popular papers on natural history, the past decades it transformed into the journal for nature conservation and management. Recently all issues up to and including 2006 were collected on DVD. This allowed us to calculate the relative importance of papers with  keywords in a number of fields, and their dynamics over time, rather simply. The relative occurrence of geology, systematics and community declined, whereas that of ecology and ecosystem increased together with monitoring. The relative occurrence of land reclamation strongly declined, whereas that of acidification, succession, encroachment of tall forbs and grasses increased. The relative importance of the passive terms nature conservation and nature reserve decreased, whereas that of the more active nature management and nature development increased. The relative importance of the management practices burning and chopping declined, whereas that of grazing, impoverishment of the soil, re-introduction and National Ecological Network increased. The relative importance of the ecosystem dune declined, whereas that of forest increased, and that of heathland fluctuated. Animal groups have 90% of the relative importance of the species groups, and plant groups 10%. Within the group of animals the relative importance for birds, mammals and insects amounts to 80%. The biggest change is the decline of the relative importance of insects. Over all, however, the journal paid attention to almost all animal groups to some degree during the last century. Red List species are not more often mentioned since the establishment of the Red List concept. Many of the Red List species were more often mentioned decades ago than recently. These changes in relative importance of issues can be related to political, social, physical and scientific changes.

    • pdf downloaden Soil acidification seems to play a key role in the regeneration problem of Common juniper
    • E.C.H.E.T. Lucassen, L. Loeffen, J. Popma, E. Verbaarschot, E. Remke, S. de Kort & J.G.M. Roelofs
    • Causes for the regeneration problem of Common juniper (Juniperus communis) in the Maasduinen area (The Netherlands) were studied. Areas with and without regeneration were compared. Twelve areas  showed no signs of regeneration. Four areas showed some regeneration and three areas showed strong regeneration. On three locations in most of the areas soil material (0-100 cm) and plant material (leaves and berries) were sampled. These samples were chemically analysed, tetrazolium tests were carried out to test the seed viability of the berries and the degree of scale insects (Carulaspis juniperi) infestation was determined.   

      The results show that locations with less regeneration had a lower base saturation indicating a stronger acidification of the soil. Soil acidification generally leads to lower nitrification rates which very likely explains the low ammonium concentration at the soil adsorption complex of locations with regeneration. In addition, due to soil acification, the concentration of soil extractable Al and the Al/Ca ratio of the soil adsorption complex at locations without regeneration decreased to values indicative for Al toxicity. As a consequence, the juniper trees also developed higher Al concentrations, lower Ca concentrations and a higher Al/Ca ratio in berries and leaves. In addition, the blue berries and the needles showed a decrease in P and K concentration and higher N/P and N/K ratios. The higher Al intrusion and the lower P uptake may be caused by the damaged root system including mycorrhizas. The infestation with mites increased with increasing regeneration, which may be related to the relative high concentrations of nitrogen present leading to production of ‘cheap’ amino-acids. Eventually, the vitality of the trees and the viability of the seeds decreased with decreasing regeneration class.     

      The results indicate that increasing the base saturation (> 43%) of the first 20-30 cm soil, may be an important restoration measure for sustainable development of juniper populations as it will lead to increased production of viable seeds.