De Levende Natuur nummer 1 van 2020 (English summary)

How to preserve Creeping marshwort? 

S. van der Meer, J. van Zuidam & L. Tijsma 

Creeping marshwort (Apium repens) recolonized four nature development areas in the province of Noord-Brabant after restoration measures. To preserve the species in these areas, different management regimes were tested for two years. The big challenge in managing existing populations is to create and maintain sufficient openness in the vegetation, thereby creating high light availability and physical space for survival and expansion of creeping marshwort. In one of the four areas (named ‘de Groespeel’) grazing with large cattle was very effective in maintaining both a low vegetation (due to grazing) and sufficient open soil (due to soil disturbance by movement of cattle). This lead to expansion of the species in the wetter parts of the area. In most areas, managing vegetation structure by mowing did not result in the desired openness. High productivity of the vegetation caused fast regrowth after mowing, limiting the time for creeping marshwort to expand in open areas. Additional top soil and moss removal proved effective in some cases to maintain openness for a longer period, with colonisation by creeping marshwort as a result. Additional to creating physical space, top soil removal also resulted in germination from the seedbank, creating new opportunities for population expansion. The activities in this project have contributed to the survival of creeping marshwort in all four areas. However, in three areas the populations are still small and unstable which can easily lead to local extinction. The project showed that local conditions strongly determine the effectiveness of different measures. Creeping marshwort, with its ephemeral populations, is highly dependent on a long-term persistent soil seedbank. Hence, it is essential that flowering individuals produce high quality seeds. It is currently unclear whether many outcrossed seeds are produced since creeping marshwort is also highly clonal. By performing pollination experiments in the near future we hope to learn more about the life cycle of creeping marshwort in the four studied populations. 

Autumn activity, autumn and winter quarters of serotine bats 

P. van Hoof, T. Molenaar, P. Lemmers, J. Jeucken & K. van Breemen 

The serotine bat (Eptesicus serotinus) is quite common in The Netherlands, but declining in numbers. Much is unknown of its activity and quarters during autumn and winter, making adequate protection difficult. To gain more insight, individuals from the serotine bat colony in the St. Matthias Church in Castenray were tagged and monitored. In August and September 2017, 16 serotine bats were tagged with radio transmitters. The study lasted for 12 weeks, from August 21st to November 11th 2017. The bats were followed by cars, equipped with antennas and receivers. During the day known quarters were checked. New quarters were located and their characteristics were noted. During the study, 39 quarters were located outside the St. Matthias Church. Most were found within a 6 km range of the church. Three quarters were located at a distance of 9,5 km and one 13 km away. The tagged bats often changed quarters during the study, up to six times per individual. They usually did not use the same quarter twice. There was almost never more than one individual in one quarter. During the course of the study the temperature did not drop below freezing, making it uncertain if the serotine bats change their behavior during cold periods. Additional research is required to confirm whether the outcomes of this study also apply to colonies in different situations, like residential areas. 

How effective are nest boxes as mitigation for common swifts and house sparrows? 

G. Verburg 

Birds that predominantly nest in cavities in buildings, such as the common swift and the house sparrow, often see their nesting opportunities decline when old buildings are renovated or replaced by new buildings. Because their nests are legally protected, the Dutch government suggests artificial nesting space as a mitigation method. But how effective are the specially designed nest boxes, bricks and roof tiles for the breeding population of these two bird species, and what determines their success? I reviewed various evidence-based sources of literature on this subject to get an overview of what is known, and also of which knowledge is currently lacking. I found that for the common swift, the number of breeding pairs using artificial nesting facilities varies greatly per city - from virtually none in Leiden and The Hague and 8% in Amsterdam to 25% in Amersfoort. The reasons for this variation are unknown, although some authors speculate that common swifts have developed a particular local ‘breeding culture’. In general, important factors in acceptance of nest boxes were their location (preferably on the same spot where the original nests were) and necessity (swifts will discover them if they have no other option). For the house sparrow, despite it being listed as endangered since 2004, surprisingly little is known about the importance for nest boxes for the population. The sparrow often appears in nest boxes targeted at other species, while it is also noted for its slow acceptance of artificial nesting space. I therefore recommend more research into what determines the selection of nesting location by the house sparrow. For the common swift, it would be interesting to find out what determines the huge variation in nest box use between different cities. Filling both knowledge gaps may increase the effectiveness of artificial nests in supporting the breeding population of both species. 

Effects of top soil removal on vegetation and butterflies 

M. Wallis de Vries & R. Bult 

Nature restoration after topsoil removal on former agricultural land is important to achieve the nature network in the Netherlands. The short-term developments are often promising, but insight over the long term is lacking. This paper presents the monitoring of nature restoration over a 25 year period across eight study areas in the northern Netherlands. From the characteristic species of vascular plants for heaths and semi-natural grassland in the vicinity, an average of 53% established in the topsoil removal areas. Between 2001 and 2017, the establishment of characteristic species continued to increase for species from dry and wet heaths and notably for acid grasslands. Species from dry pioneer communities declined with the closing vegetation cover. A full recovery of the species community is still strongly hampered by absence of sources in the vicinity and by limited dispersal from existing sources to the restoration areas. For butterflies, both species richness and abundance of the 10 target species continued to be lower than in the surrounding area. Source populations of the rare species were often not available in the vicinity anymore. Between 2002-2003 and 2017, the proportion of butterflies from target species more than doubled in the topsoil removal areas, whereas it did not increase significantly in the surroundings. Habitat quality for the target butterfly species had increased slightly, but remained a more important bottleneck for establishment than isolation from source populations. The study also indicates that the success of topsoil removal strongly depends on subsequent management. Without grazing, the areas are rapidly overgrown by pioneer trees. Low-intensity grazing in combination with additional targeted cutting of rough vegetation is recommended for an optimal development.  

The large-scale eradication of Crassula helmsii on Terschelling 

M.van de Loo, F. Soontiens, Wouter de Vries & J.van der Loop 

The eradication of the aquatic invasive species Crassula helmsii fails mostly when the species is abundant, widespread and not isolated at the infested location or when re-contamination can easily occur. In 2018 an eradication of 4,5 ha has been attempted in three moist dune systems on the Wadden Island Terschelling, the Netherlands, in and near the protected habitats of the Natura-2000 area. A six step method has been carried out: 1. marking of the infestation, 2. the construction of a thoroughfare to and from the infected areas, 3. the excavation of the entire topsoil, 4. transport of extracted soils to the storage laid out in a dry dune system, 5. a check whether the excavation is clean and 6. replenishing the excavation with clean sand to create an additional security of C. helmsii removal and restoring the hydrology of the ecosystem. Aftercare consisted of increasing the resistance of the ecosystem against invasions of C. helmsii by manipulating succession and a monitoring program whereby the effectiveness of the measures was assessed every 6 weeks. Afterwards, the fast growing plant has not been observed for one year on site.