De Levende Natuur nummer 6 van 2008 (English summary)


DLN 2008-6

Help the Common spadefoot!

M. Zekhuis & F.G.W.A. Ottburg

The Common spadefoot (Pelobatus fuscus) occurred mainly in mesotrophic waters on sandy soils. Near these reproduction waters, they need bare soil were they can easily dig in. This type of habitat is not rare in the east of The Netherlands. In spite of this, the Dutch population decreased since 1990 with ca 60% and is at the moment endangered. There are 35 small populations left and most of them (70%) depend on only one reproductionwater! The last 15 years a large number of protective measures for both water- and land habitats have been taken, but so far the effect seems very low.
The authors suggest that in most small populations the lack of recovery when habitat quality is restored is due to the loss of genetic variation that prevents populations to grow. Therefore they advise to start with the addition of new genetic material (genetic resque) to small populations and reintroductions at short notice.

Koolmansdijk: pearl in the Achterhoek thanks to successful nature restoration

Koolmansdijk is a small nature reserve in the Achterhoek (eastern Netherlands). The former reserve (6ha) was extended with 50 ha’s of arable fields and agricultural grasslands. The top soil of these agricultural lots has been removed, following the weakly undulating relief. On the edge of the old part of the reserve and the former agricultural lots a wooded bank occurred, which has been removed and subsequently has been sod cut. Within six years after measures were taken the number of endangered species of the Red List increased form 18 to 27. Moreover, this number exceeds the number that has been recorded in the 1950s, which is exceptional. Simultaneously, endangered plant communities of fen meadows (Cirsio dissecti-Molinietum with many species of calcareous fens), heathlands (Nardetea), pioneer stages (Cicendietum filiformis) and shallow soft waters (Littorelletea eleocharitetum multicalis) have established. Key factors of this very successful restoration are: (1) the specific position of the reserve in the regional hydrological gradient: a steep altitudinal gradient from a plateau to a basin in combination with the narrowing of the impermeable base of the aquifer, resulting in an intense upward flux of groundwater, (2) top soil removal in such a way that the soil seed bank of many disappeared species has been exposed and (3) the occurrence of a species-rich small nature reserve in the vicinity, favoring the dispersal of propagules of endangered species.

Chara braunii Gmel., the first record in The Netherlands after reconstruction of fish ponds

J.H.P. Bruinsma & P.J.J.J. Voorn

Chara braunii is a cosmopolitan species that is extremely rare in Western-Europe. In 2006 C. braunii was found for the first time in The Netherlands. Plants grew in five former fish ponds near Valkenswaard (51° 22’ N, 5° 29’ E). Nowadays fish farming ponds are no longer profitable because of increased predation by fish eating birds (mainly Ardea cinerea and Phalacrocorax carbo) and because of increased competition by fish farming in Eastern and Southern Europe. The fish ponds were already well known for the high conservation value: mainly rare fish eating birds and, in a transition zone between a heath and the fish ponds proper, water plants. The fish ponds were laid out in 1900. In the 1950’s their use was extremely intensified, which, among other things, left an organic debris layer of several decimeters.
The fish ponds were obtained by the local waterboard (Waterschap de Dommel) and the provincial nature conservation organisation (Brabants Landschap). In 2005 several measures were taken: remeandering of the stream that feeds the fish ponds (the Tongelreep), construction of a fish passage, retention of water in some ponds to decrease changes in water levels in the stream, increasing the length of watercourse through the ponds while assuring that it will always follow the same route, and removal of the debris layer in five ponds. Small numbers of fish will be introduced and it is intended that some ponds will have a cyclic water regime while others will have permanent water.
C. braunii was found growing on sand in clear, rather eutrophic water, in four of the five recently dredged ponds in the first year after reconstruction. In the second year C. braunii decreased significantly. However, it was then found in a pond that had been left dry the year before. C. braunii is accompanied by some common species but also by some nationally or locally rare and endangered species such as Elatine hexandra, Potamogeton gramineus, P. x angustifolius, P. obtusifolius and Ranunculus aquatilis var. diffusus (Ranunculus trichophyllus).
Fish ponds are a common habitat for Chara braunii. It is suggested propagules (oogones) were introduced with the import of fish from Belgium or Hungary.

Prunus serotina as an invasive species in Dutch coastal dunes

A. Ehrenburg, H.J.M. van der Hagen & L. Terlouw

In the coastal dunes of The Netherlands invasive non-indigenous plants are proliferating at an alarming rate, especially during the last 10 years, for example Prunus serotina (Black berry). Often the species exist already for many years in an area, but can rather suddenly increase at an alarming rate in number and cover. From P. serotina survey of the Amsterdamse Waterleidingduinen in 2004 and partly in 2006, an increase of 25% in cover was found especially in seabuckthorn scrub and partially decalcified dune-grasslands. Due to their invasiveness the species threatens designated Natura 2000 dune habitats, and it is therefore urgent to find effective management practises. This is not an easy task as invasive species such as P. serotina are very successful due to favourable species characteristics and advantageous environmental circumstances. In the present study the rapid increased P. serotina was due to the warmer and wetter circumstance during the last decades, the lacking of rabbit grazing, and the lacking of natural soil pathogens. Once P. serotina is established, their management is labour intensive, costly and needs to be continued over many years. Hence, it is of the utmost importance that management practices come into effect as soon as possible after sightings of P. serotina! As for each possible invasive species, specific methods of management are needed, it is important that European and national legislation on control of exotic invaders is implemented as soon as possible. This in order to be able to protect Natura 2000 habitats in the most effective way, as well to find sufficient financial support for its management.