De Levende Natuur nummer 6 van 2018 (English summary)


DLN 2018-6

English Summaries

What perspective will the small opening of Haringvliet locks bring to the Haringvliet area and the upstream areas?

G.L. Ouweneel

The rivers Rhine and Maas form their delta in the southwest of the Netherlands. One of the delta streams is the Haringvliet. In the context of the Dutch Deltaworks this river lost its open mouth to the North Sea due to the construction of the Haringvlietdam in 1970. This closure was a major event for nature and environment in and around the Haringvliet. The former estuary became a freshwater river and the tidal difference was reduced to 30 centimeters. The bird species who are used to feed on tidal mudflats disappeared. Nevertheless, after 1970 nature conservation managed to achieve important results in and around the Haringvliet. Greatest success was the depopulation of the 1000-hectare island of Tiengemeten, that was transformed by Natuurmonumenten into a ‘nature island’. Characteristic natural values in the Haringvliet area are breeding waders like Black-tailed Godwit and Ruff on the outer dike grasslands and during winter large numbers of geese. Spoonbills and several tern species including Sandwich Terns are used to breed on artificial islands, which were constructed for breeding coastal birds. In 2000 Dutch authorities launched a plan to open the Haringvliet locks for 10% during  95% of the time. This measure would bring back tidal differences and allow migratory fish to shuttle up and down from the North Sea to their upstream situated spawning-grounds. The upstream nations constructed hydraulic facilities so that these spots came within reach again for migratory fish species. Now, the Dutch authorities took the decision called ‘Kierbesluit’, which means if circumstances allow, the Haringvliet locks will be opened. However the ajar will be so small that only migratory fish will have a chance to come in. The tidal difference on the Haringvliet will remain roundabout 30 centimeters, the important salt/fresh contact zone for foraging waders will be still missing. At the same time a public lottery made available a considerable amount, named ‘Droomfonds Haringvliet’, for extension and restoration of existing nature reserves along the Haringvliet as well as for the construction of breeding grounds for coastal bird species. Some new hides will be constructed. Given the location of the Haringvliet area is situated just south of the densely populated urban concentration of the western Netherlands, it is to be welcomed that nature management can extent and strenghten its position. Regarding the reopening of the Haringvliet locks it is to be regretted that this measure is exclusively aimed at restoring the position of migratory fish. To further improve this, it is advisable to impose restrictions on the current fishing activities on both sides of the Haringvliet locks.

Recover of meadowbirds in a wetland in NW-Overijssel, The Netherlands, after reducing red fox

O.H. Brandsma

The grasslands of Giethoorn-Wanneperveen are located in NW-Overijssel and are a part of the wetland ‘De Wieden’. De Wieden is a peat-bog area consisting of lakes, pools, swamps and grasslands. In 1987-2017 the effects of several types of grassland management on meadow birds were investigated. In 80-90 % of the study area, mowing and grazing have been restricted to improve breeding circumstances for  meadow birds. In the nineties Red fox rapidly expanded from the higher sandy soils in the eastern parts of the Netherlands to the low (wet) grassland areas and also to ‘De Wieden’. This article shows the severe effects of the establishment of the Red fox on the meadowbird populations in a 252 ha meadowbird reserve. This area holds high densities of Snipe, Black-tailed godwit, Redshank, Curlew, Lapwing, Shoveler and Garganey. From 1987 until 1993 almost all meadowbird species increased. After the establishment of Red fox the numbers of all meadowbird species rapidly decreased. In order to protect meadowbirds, from 1997 onwards Red foxes have been hunted intensively. Since 2003 the depredation by Red foxes was reduced, meadow bird chicks grew up again and the meadowbird population recovered. In 2017, almost all meadowbird species were back at the same level as in 1990.   

How climate change affects flora and fauna in the Netherlands

C.A.M. van Swaay, C.A.M. van Turnhout, L.B. Sparrius, R.H.A. van Grunsven, J.R. van Deijk, A.J. van Strien & S. Doornbos

Climate change has a profound effect on the distribution of numerous plant and animal species. However, whether and how different taxonomic groups are able to track climate change is still largely unclear. Following a method developed by Devictor et al (2012) we measure changes in the Community Temperature Index (CTI) over time for breeding birds, butterflies, moths, dragonflies and plants in the Netherlands. All groups show a significant change in CTI, which means that communities are changing in a way that thermophile species got relatively more abundant than thermophobe species. The rise in CTI is approximately ten times slower than the real rise in temperature. This means that although communities are changing, they react slower and have the risk to 'lag behind'.

Management of autochthonous trees and shrubs in Natura 2000 forest habitats

N.C.M. Maes, E. van den Dool, K.A.O. Eichhorn, R.W.A. van Loon & P. Veen

The management plans for two Natura 2000 forests were analyzed to assess their treatment of indigenous tree and shrub species. The forests considered were Savelsbos (Beech-oak forest and Oak-hornbeam forest on calcareous and loamy soils) and the Veluwe (Beech-oak forest, Old oak forest and Alluvial forest on sandy and loamy soils). These forests contain large populations of autochthonous trees and shrubs that are now fairly rare in the Netherlands (e.g. Beech, Sessile oak, Small-leaved Lime and Large-leaved Lime), as well as a range of very rare species today occurring only in small, threatened populations, such as Crab apple, European white elm and Cornelian cherry. Remarkably, the management plans lack any measures directed towards these autochthonous trees and shrubs, despite they are forming an integral part of the forest habitats. It suggested that the management plans were established without using the relevant information available on tree and shrub species, even though the overarching objective of N2000 is to ensure due preservation of natural habitats and wild populations. It is recommended that the management plans be augmented to include measures directed specifically towards characteristic autochthonous trees and shrubs, to ensure preservation and enhancement of quality.

Alien species on the Dutch Wadden Sea islands

R. Lensink, T.M. van der Have, R.J. der Haterd, J.A. Inberg, B. Achterkamp & D.M. Soes

Among the 1490 alien species found in the Netherlands and under consideration in this review approximately 300 of them were found on one or more Wadden Islands in the period 2005 - 2014. The most numerous group are plants, followed by Crustacea. Most alien species are found on the largest island of Texel and fewest on the smallest habituated island of Schiermonnikoog. The number of species on the uninhabited (and much smaller) islands and sandbanks is far less. In this study 47 alien species are in the category ‘black list’ or ‘watch list’ according to the ISEIA-protocol. Among those, 29 species are an actual risk for nature on the Wadden Islands, mainly because they occur on one or more islands. 18 species are a potential risk, mainly because these species are lacking on the islands at this very moment. The following species are a major threat for Natura 2000 goals: Campylopus introflexus; Prunus serotina; Vaccinium macrocarpon; Acer pseudoplatanus; Cotula coronopifolia and Rosa rugosa. Spartina anglica is a major threat as well, but also an important species in a Natura 2000 habitat type. This seems to be contradictory.