De Levende Natuur nummer 4 van 2007 (English summary)


DLN 2007-4

Establishment of inland brackish plant communities

Bakker, J.P., H.E. Wolters, M. Smith, S. de Vries & Y. de Vries

Along the north-east coast of The Netherlands, plans have been developed to establish inland brackish plant communities on previously agricultural land. Brackish abiotic conditions are created through the removal of the topsoil and the creation of ditches and/or depressions to induce saline seepage. In the present paper we studied the possibilities of spontaneous establishment of brackish vegetation (from the soil seed bank or through natural dispersal) and establishment after the introduction of plant material containing the target species at two restoration sites. Our selection of target species is based on 1100 descriptions of brackish and saline plant communities recorded in the period 1936-1999 along the north-east coast of The Netherlands. Plant species occurring with a > 50% frequency in a specific plant community were classified as target species. This resulted in 47 target species of which 18 were classified as freshwater species, 14 as brackish species and 15 as saline species.

Because dispersal of propagules is likely to be a constraint, we sowed a specified number of seeds of eight species of saline habitat in the Klutenplas, where the topsoil had recently been removed. Of these species Aster tripolium, Glaux maritima, Limonium vulgare, Plantago maritima and Spergularia media survived for two growing seasons, whereas the annuals Salicornia spp. and Suaeda maritima did not. Because collecting seeds of specific species is time consuming, we examined whether the transference of driftline material, collected from salt marshes seaward of the seawall protecting and deposited after storm and high water, would result in successful establishment of the target species. Because of the promising results of a pilot study in the Emmapolder, a large-scale transference of driftline material was carried out in the Klutenplas. After one growing season, ten target species were recorded in the part spread with driftline material, whereas those species were absent from the control plots or significantly less abundant. 11 % of the target species of fresh habitat, 36 % of brackish habitat and 80 % of saline habitat were found. We conclude that the spreading of driftline material is successful for establishing target species growing on adjacent salt marshes in inland brackish sites. Target species of brackish and fresh habitat have to be introduced by spreading of hay from a nearby brackish plant community.

Restoration plan Naardermeer a great success

Boosten, A.

Naardermeer nature reserve is a fresh water marsh area, established as the first Dutch nature reserve in 1906. It is a natural lake, unlike the adjacent marshland reserves which originated as a result of peat digging. Since the 1970’s its natural values decreased, mostly related to deteriorating water quality. In 1992 a Restoration Plan with an overview of all negative developments as well as detailed suggestions on how to restore, keep or improve natural values was launched. The measures taken, affected both quantity and quality of surface water, aquatic and terrestrial ecological communities, nature management, enlargement of the reserve and ecological infrastructure. At present, 13 years from the start, 10 out of 14 measures have been completed. The remaining measures have been started. The clear lakes and ditches now have visibility to the bottom and have an abundant diversity in diatoms, macro fauna and water vegetation including increasing numbers and abundance of rare and indicative species. Terrestrial plants and marshland birds have increased too. The integral approach has worked, but we must remain keen on threats, as shown by the recent plans to build a motorway nearby the reserve.

Restoration of cut-over Sphagnum bog-vegetations in the Dutch Peel-area by rewetting

Boom, B.W.A.F.H. van den, Ph. Bossenbroek & J. Holtland

Large-scale anthropogenic peat extraction in the 20th centrury has led to the destruction of almost all raised bogs in The Netherlands. In the Dutch Deurnse Peel and Mariapeel area less then 2700 ha of severely damaged bog relict was all that remains of a raised bog system that once stretched over 30.000 ha. The remaining bog relicts lost the characteristics of ombrotrophic bog systems due to peat cutting and drainage. Because of the effects of water draw-down the cut-over bogs are largely dominated by Molinia caerulea and Betula pubescens.
The present-day scarcity of typical bog vegetation made the restoration of cut-over bogs an important issue. In the Mariapeel, restoration management has been based on the strategy of inundating extensive areas of land by creating a 'cascade-model' based hydrological structure

As a result of these rewetting measures, within a period of ten years a rapid expansion of submerged Sphagnum cuspidatum dominated vegetations have developed in both the Mariapeel and the Deurnse Peel. On a small scale the new formed Sphagnum cuspidatum has become buoyant and in future this proces may increase further. These floating rafts can then be colonised by other Sphagnum mosses as Sphagnum fallax, and in time other bog mosses as Sphagnum papillosum and vascular plants may establish. In the Peel-area this bog succession has not yet occurred, and is hampered by the nutriënt rich peat quality (caused by the agricultural history of the surroundings) and by fluctuations in (ground)water levels.

Staatsbosbeheer aimes at further stabilising these groundwater levels in the Deurnse Peel / Mariapeel by enlarging the hydrological buffer zone around the nature areas. Thus, Sphagnum dominated bog vegetations in the Peel area have a new chance of sustainable development in the future.

Red foxes in the Dutch dunes and implications for fox management

Mulder, J.L.

Around 1968 the coastal dunes of Holland were colonized by foxes (Vulpes vulpes L., 1758). Between 1980 and 2000 the ecology of this unmanaged fox population was studied in three research projects, about 15, 20 and 30 years after the first arrival of the fox respectively. Compiling the results of these studies revealed a highly territorial fox population, apparently controlled by density dependent factors. Territory size changed from about 130 ha 15 years after the first arrival of the fox to 55-60 ha 20-30 years after. Population density was about 2.5, 9.0 and 6.5 foxes/100 ha respectively. In recent times a considerable proportion of itinerant foxes, including females, were present year round, which was not the case just after arrival. Mortality, almost exclusively by natural causes, was high: about 60% during the first year of life and about 25% at the age of 1-4 years. Rabbits were the main food source, even when rabbit numbers were low. From the population dynamics of the fox we can learn that killing foxes during autumn and winter will hardly have any effect on fox numbers in spring. If vulnerable prey species need protection (at all) against fox predation in the breeding season, prevention needs attention first. Killing foxes will only have a chance to be effective when executed in late winter and early spring.