De Levende Natuur nummer 1 van 2015 (English summary)

The Common Spadefoot in The Netherlands: demise or ‘merely’ a bottleneck?

W. Bosman, R.P.J.H.Struijk, M. Zekhuis, F.G.W.A. Ottburg, B. Crombaghs, D. Schut & P. van Hoof

The Common Spadefoot occurs on the Pleistocene sandy soils in the Netherlands. Until the year 2000, the species was historically known for its presence in 111 5x5 kilometre grids. Since the 1950s the Common Spadefoot has shown a decline, mainly caused by habitat destruction and deterioration, but also acid rains and the introduction of predatory fish. Despite conservation measures such as restoration and creation of ponds and to a lesser extent terrestrial habitat, population sizes and its distribution did not increase. Between 1990 and 2000, only 41 5x5 kilometre grids were occupied by the species. Between 2001 and 2013 this remained the same. Monitoring data show that in 74% of the current populations, chorus sizes are extremely small (≤ 10 calling specimens). This low number could possibly have led to the decrease of the genetic variation, therefore increasing the possibility of the extinction due to calamities.

Program for (re-)introduction of the Common Spadefoot

B. Crombaghs, I. van Bebber, J. van der Zee, D. Schut, P. van Hoof, J. Janse, R. Zollinger, F.G.W.A. Ottburg, M. Zekhuis, J. van der Weele & H.A.H. Jansman

Since 2011 an ambitious program for (re-)introduction of the Common Spadefoot in The Netherlands has been set up.  This article describes the methods and results of breeding the collected strands in a controlled in- and outdoor setting. In view of vulnerability, indoor breeding is preferred during the first six weeks. Thereafter the outdoor breeding is more beneficial. In the last four years, up to 90.000 larvae and/or juveniles were released in fifteen present-day habitats, former habitats or areas regarded suitable as a new potential habitat. Last year, an increase in recapture of juveniles and adult toads as well as observed chorus activity in these areas makes us hopeful.

Is there a future for the Common Spadefoot (Pelobates fuscus) in The Netherlands without intensive care?

F.G.W.A. Ottburg, B. Crombaghs, W. Bosman, M. Zekhuis, D. Schut, P. van Hoof, R.P.J.H. Struijk, R. van Westrienen, R. Zollinger, H.A.H. Jansman & R.P.H. Snep

After decades with a dramatic decrease of the Common Spadefoot populations in the Netherlands there is continuous effort needed to conserve the few remaining locations where the species still exists these days. This raises the question: do we continue putting large efforts in Common Spadefoot conservation, also on the long run, or do we aim for a situation in which the species is able to survive on its own? As start for a debate, this paper presents three scenarios in which the underlying landscape systems – instead of conservationists – should be capable to support Common Spadefoot: 1) a new river floodplain management (resulting from climate-proofing strategies), 2) the fast-growing biological agriculture and 3) modern nature parks. The first two provide – though out of focus in current conservation - interesting options because of their landscape dynamics and the socio-economic demand for these landscapes. For the third, the natural park, it is unclear whether the necessary habitat dynamics and conservation funding will be available on the long run. This paper calls for broadening the conservation view and explore options outside the current ‘intensive care’ situation. Options that may offer a solution for the long term survival of this remarkable amphibian species.

More dynamics in the National Park the Biesbosch after finishing the nature restoration

J.A. Sluiter & F.H. Saris

The Biesbosch is important for the water safety of the cities of Dordrecht, Gorkum and Geertruidenberg. A number of polders in the Biesbosch are currently being de-poldered as part of the Room for the Rivers project. The main purpose of these activities is to increase the conveyance capacity of the river Rhine during extreme discharge. As a result the hydrodynamic processes have become more and more important in the Biesbosch. Erosion and sedimentation are visible in the nature restoration areas. These processes lead to a variety of small scale nature and gradients of wet and dry, sand and mud, deap and shallow. New species have appeared in the nature restoration areas (e.g. White-tailed eagle) and species have augmented (aquatic plants, fish).The question if these changes and increase of species are permanent, can not be answered for the Biesbosch: this fresh water tidal wetland is strongly influenced by hydrodynamic processes and will change every day.

The Biesbosch is important for the water safety of the cities of Dordrecht, Gorkum and Geertruidenberg. A number of polders in the Biesbosch are currently being de-poldered as part of the Room for the Rivers project. The main purpose of these activities is to increase the conveyance capacity of the river Rhine during extreme discharge. As a result the hydrodynamic processes have become more and more important in the Biesbosch. Erosion and sedimentation are visible in the nature restoration areas. These processes lead to a variety of small scale nature and gradients of wet and dry, sand and mud, deap and shallow. New species have appeared in the nature restoration areas (e.g. White-tailed eagle) and species have augmented (aquatic plants, fish).The question if these changes and increase of species are permanent, can not be answered for the Biesbosch: this fresh water tidal wetland is strongly influenced by hydrodynamic processes and will change every day.

The willows of the Biesbosch

A.A.G. Zwaenepoel, E.R. Cosyns, N.C.M. Maes, R.W.A. van Loon & T.O.V. Muusse

During  2012 and 2013 we did a survey about willows in the National Park Biesbosch. On each island we determined all willow taxa and mapped their distribution. Our aim was to look for all known willow taxa that have been introduced in this area in order to be able to select plant material that might be originally indigenous to the area. On the other hand we looked for cultivars which were related to the traditional 19th and early 20th century osier holts. Mapping their distribution could help to select areas worth for restoration of these traditional osier holts and also areas with high potential for new wilderness. Next to the field research we did some historical research, in order to get a complete overview of cultivated willow taxa in the Biesbosch. Finally, we also interviewed some key persons to know more about the osier holts and the evolution of the landscape during the past decades. As a result we were able to locate and describe the distribution of about 50 willow taxa and to relate local names to botanical names. We advocate to not promote oversimplified the Biesbosch as primeval forest. For this human impact on the ecosystem has been too great. Although Salix alba stands largely dominate the landscape a lot of plant taxa are not indigenous but originate from willow cultivation or are exotic. Therefore, we consider it equally important to remember at least the traditional willow cultivation as well.