De Levende Natuur nummer 5 van 2017 (English summary)

European bison – recreant interactions in two Dutch nature reserves: Kraansvlak and Maashorst

A.M.P. Brouns, D.J.M.J. Haanappel, L. Linnartz & M.J. Wassen

For over 25 years natural grazing has been used in Dutch nature reserves for several reasons. Most importantly because large grazers belong in the Dutch landscape and play an essential role in the natural system. Grazing, browsing, cutting, rolling and rooting are an important addition to the natural dynamics, contributing to the resilience and diversity of nature. Additionally, their activities reduce natural succession from open short-growing herbaceous vegetation to woodland and increases habitat diversity offering opportunities for many other plant and animal species.

Since large grazers are also introduced in areas that are open for recreation close encounters between visitors and grazers are inevitable. This study aims to gain insights into how European bison (Bison bonasus) responds to several types of recreational visitors.
We simulated standardized interactions of three types of recreational visitors (hiker, jogger, mountain-biker) with two herds (Kraansvlak, Kennemerdunes and Maashorst Noord-Brabant) consisting of 16 and 11 individuals, respectively. In both areas the animals experience minimal human intervention. They are not supplementary fed and are self-sustaining.

Our results show that the bison most common reaction to the three types of recreational visitors is to look up. There is no significant difference between their reactions upon these recreationists. Approaching and relocation are less common behaviors. Additionally, the bison appear to be very alert to a leashed dog and they approach the visitor with dog regularly (no statistics due to insufficient number of tests). The investigated herds showed no aggressive responses to recreationists except for one case in Maashorst where the test person and the observer were too close to the herd at the time of the incident. Importantly, the Maashorst herd showed significantly more than the herd in Kraansvlak expressions of irritation like shaking the head and stamping their hooves on the ground, irrespective of the type of recreationist. Test persons were also more often approached in Maashorst than in Kraansvlak.

We conclude, that here is no immediate reason to keep recreational visitors from areas that are inhabited by bison. Yet, the study is limited in scope and time, and can therefore not conclude that visitors and bison go together safely under all circumstances. Furthermore, we advise to build-up the recreational pressure slowly when areas inhabited by bison are to be opened for the public and to communicate comprehensive education to the public. Application of strict rules and enforcing them is of great essence.

Plant remains in the stomachs of northern fulmars: a measure for pollution

W.J. Kuijper, C. Vermeeren, A. Meijboom & J.A. van Franeker

The northern fulmars pick up everything that floats on the water surface, including plastics, and therefore the stomach contents are a measure for the pollution of the sea. As a small part of a pollution research in the North Sea the plant remains in the stomachs are analysed. They are divided in plants from natural vegetations (wild plants) and plants originating of several human activities (‘garbage’). The combined regional results support those of the monitoring of litter.

Can Griend ‘walk’ again?

L.L. Govers, T. van der Heide, H. Olff, Q.J. Smeele & A. van der Eijk

Griend is a small island located in the middle of the western Dutch Wadden Sea, well-known for supporting tens of thousands of breeding birds and roosting shore birds. This dynamic island used to ‘walk’ across its surrounding mudflats in south-eastern direction with an average speed of 7 m/year. Although the island was moving, both erosion on the north-western side and expansion on the opposite site were well-balanced until the 1930s. The island became smaller and smaller after the construction of a large dam (‘Afsluitdijk’) that changed the sediment dynamics of the entire tidal basin. To conserve Griend, many restoration measures have been taken in the past 40 years, but none of these lasted a long time. Recent developments led to new insights in the functioning of dynamic Griend, which is now considered a chenier-island instead of a barrier island. The dynamic character of this type of island is guided by storm floods that result in deposition of shell-rich sand bars on the island. This ‘chenier’ shelters an area in which a salt marsh can develop. Currently, external processes feeding the island are diminished due to a deteriorated habitat richness on the surrounding mudflats. By experimentally enriching the mudflats by mussel bed construction and sowing seagrass seeds (Zostera marina) researchers are currently investigating if this could help Griend to become a balanced island again.

Effects of muskrat on littoral stands of common reed

P. J.J. van der Burg & J.E. Vermaat

Stands of water reed have declined greatly in the Netherlands during the 20th century and the literature points to several causes. Adverse sediment and water quality, recreation pressure or geese grazing are most frequently mentioned, whereas muskrat grazing is not, despite its rapid expansion and high densities in The Netherlands since 1970. In a multi-year, split-plot exclosure experiment (2013-2016) the effect of muskrat grazing was assessed on the establishment into the shallow water foreshore of common reed and other macrophytes. In the exclosures, reed establishment and expansion rapidly led to significant differences in shoot densities of common reed, branched bur reed and several species of submerged waterplants, compared to controls. This occurred despite the reportedly poor sediment and water quality at the study site (Lake Kalverbroek, Reeuwijkse Plassen). It is concluded that muskrat herbivory should not be ignored in the assessment of reed bed decline and in the design of wetland restoration programs.

Long-term fertiliser experiments in grasslands of Loefvledder, Drentsche Aa

J.P. Bakker, Y. de Vries & C. Smit

Restoration of species-poor agricultural grassland to species-rich grassland is often strived after by impoverishment of the soil, namely, cessation of fertiliser application and hay making. To what extent is impoverishment counteracted by mulching or compensation of the amount of removed nutrients in hay by fertiliser application? At the start of the experiment in 1973 500-600 gdw/m² was removed annually by hay making. The nitrogen concentration in hay was about 1.5%. Hence, about 50 kg N/ha/year was removed with hay. This amount is returning by mulching. The same amount was added after hay making by applying fast releasing Ammonium Nitrogen Limestone (KAS) or slow releasing Ureum Formaldehyde (UF). The effects of hay making, hay making plus KAS, hay making plus UF, and mulching were recorded from 1973-2010. Biomass declined to 300 gram/m² with hay making, and did not change with the other treatments. Number of species was 18/4m² with hay making, 13/4m² with hay making plus KAS and with UF, and 10/4m² with mulching. Number and cover of species indicating nutrient-rich soil conditions was highest with mulching, whereas number and cover of species indicating nutrient-poor soil conditions was lowest. These results are related with lowest biomass with hay making and highest amount of litter with mulching.