July 2017

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English summaries

    • European regulation on management of invasive alien species
    • L. de Hoop, J.M.M. van der Loop, J. Matthews, G. van der Velde & R.S.E.W. Leuven
    • Invasive alien species (IAS) have been introduced by humans in areas outside their native range and cause negative impacts on biodiversity, ecosystem services, economy or public health. The EU Regulation 1143/2014 aims to prevent the possession, use, cultivation, transport, trade, import and release of IAS of EU concern. Member States are responsible for the national implementation of three management approaches: 1) prevention of introduction, 2) early detection and elimination, and 3) population control and containment of species that are widely spread and cannot be cost-effectively managed. Invasive species not on the EU list but posing a regional threat to biodiversity may be placed on a national list of invasive species requiring management intervention. Successful enforcement of the EU regulation in the Netherlands requires governmental institutions, land and water managers, scientists and other parties concerned to cooperate intensively. Yet, the financing and sometimes the effectiveness of the required management measures is unclear. Further research is needed into the cost-effectiveness of management measures for invasive species and innovative system-oriented interventions to mitigate their impact.

    • Tackling invasive alien species in Flanders (north Belgium)
    • T. Adriaens, H. Verreycken & B.A. D'hondt
    • Flanders is a highly urbanized area in Europe and a global invasion hotspot. Prioritization is key to managing invasive species and requires a solid evidence base in risk analysis. The EU regulation (EU 1143/2014) on the prevention of the introduction and spread of invasive alien species currently represents a driving force for many initiatives on tackling invasive species. The drafting of pathway action plans is underway. Successful prevention will require developing greater invasion literacy with various stakeholders in the region. For a number of species of union concern, rapid response mechanisms are being laid out. Examples of rapid response on species with limited populations in Flanders include North American ruddy duck, American mink, Chinese muntjac, sacred ibis, American skunk cabbage and Pallas’s squirrel. Other non-natives such as invasive macrophytes, Canada goose, American bullfrog, giant hogweed, Japanese knotweed and himalayan balsam are being controlled to mitigate their impact. They are more widespread and require clear management objectives and/or dedicated control projects. Meanwhile, the EU regulation has been legally implemented in Flanders through adaptations of the Flemish Decree on Species Protection and Management. A number of case studies illustrate the Flemish approach. In addition, we showcase the TrIAS (Tracking Invasive Alien Species) and INVASIVESNET projects, which will contribute to streamlining dataflows on alien species and to the creation of a community of practice on invasion management respectively.

    • What to do with alien invasive species in nature conservation?
    • H.N. Siebel & M.H. Rijks
    • Alien invasive species are an increasing problem in nature management. Important lessons can be learnt from experiences so far. It is necessary to focus on the invasive alien species which are, or may become a major problem for biodiversity. A proactive approach, focusing on elimination in early stages of colonization is most feasible. For those alien invasive species where elimination is not achievable in practice, an ecosystem approach focused on changing the conditions for growth and reproduction of the alien invasive species preventing them from becoming a problem is promising, but still requires much research. For public support it is important for communication to focus on the large problems for biodiversity rather than on the invasive alien species and their foreign origin.

    • Management of invasive alien species in the North Holland dunes
    • D. Groenendijk & V. van der Spek
    • Both Waternet and PWN manage a substantial part of the coastal dunes in The Netherlands. Like most coastal dune areas in The Netherlands their areas are protected under the European Habitat Directive because of the presence of rare and unique habitat types such as grey dune grasslands and coastal scrubs. These habitat types are threatened by non-indigenous invasive plant species which are able to increase at high rates and completely overgrow the species rich dune vegetations. Especially Prunus serotina is regarded as a problem. Mapping schemes from 2004 onwards showed a strong increase in cover. However, since the management was intensified in 2011 a sharp decline in cover was noticed. Because the managed dune area is a catchment area for drinking water, the use of herbicides is no option. Measures to reduce Prunus serotina are sawing, removing of shrubs and roots, mowing and grazing with sheep and cattle, which are applied on a large scale. Other important alien species are Rosa rugosa, Berberis aquifolium and Cotoneaster species. We want to stress that it is of the utmost importance that effective management practices are applied as soon as possible after first observations of invasive alien species.

    • Successful eradication of the pallas’s squirrel in Flanders (Belgium)
    • T. Adriaens, Y. Verzelen, S. Pieters & J. Stuyck
    • In 2005, bark stripping and cable gnawing were observed in a suburban park in western Flanders (northern Belgium). The damage was linked to the occurrence of Pallas’s squirrels (Callosciurus erythraeus), a tree squirrel native to Asia. The population most probably originated from escaped animals of an abandoned zoo in the nearby amusement park. Pallas’s squirrel can reach high densities and outcompete native red squirrels. To avoid further damage to ornamental trees in the Flanders park, the park manager decided to start trapping. Low-tech mesh wire live traps were placed near the trunks of large trees, baited with peanuts, walnuts or hazelnuts. Traps were checked daily in order to minimize detention time and impact on bycatch. Digital photo traps were installed to check for remaining squirrels. During five successive capture campaigns, the number of animals removed increased to 248 in total, and by 2011, the last known animal was removed. Although the control started relatively quickly and the extent of the invasion was limited, the campaign still took over five years and required an investment of over €200,000 including 18 months of post-eradication surveying.

    • Eradication of the Pallas’s squirrel near Weert
    • V.A.A. Dijkstra & M.J.J. La Haye
    • In 2008 a population of the invasive Pallas’s squirrel (Callosciurus erythraeus) was recorded in the municipality of Weert (The Netherlands) near the Belgium border. After its discovery the Dutch government decided to eradicate this population in order to prevent a further spread of the species in The Netherlands and Belgium. During 2012 and 2013 Pallas’s squirrels were live trapped. Live trapping was important to maintain support of locals because the squirrels were trapped in their gardens. A total of 249 individuals were trapped, sterilized and replaced in various zoo’s or animal rescue centers. Since 2012 The Dutch Government forbids to trade and breed exotic squirrels.

    • Invasive ants demand a coordinated approach
    • J. Noordijk, P. Boer, A.J. van Loon & M. Brooks
    • In The Netherlands, more than 120 exotic ant species have been found. Many of these have settled and at least six are behaving invasively. Due to their high worker numbers, they locally induce changes in the flora and fauna, and cause severe nuisance. The six species are up to now only found in urban areas, but due to climate change, a future spread to nature reserves cannot be excluded. More attention for introduction prevention is needed and coordinated pest management and involving ant specialists are required to control the current populations.

    • Controlling Asian knotweed
    • J.F. Oldenburger & J. Penninkhof
    • In 2013 Probos Foundation started a field trail together with 31 organisations involved in the management of the green environment. At 119 growth locations control methods for Asian knotweed (Fallopia japonica, F. Sachalinensis, F. x Bohemica) are applied in order to find the most suitable approach for knotweed control in The Netherlands. Probos is currently undertaking final measurements on all growth location to be able to compare the situation at the start of the field trial and after 4 years of application of the control methods. The control methods tested are; covering with geotextile fabric, intensive mowing, grazing, chemical control (foliar spraying, cut stem application and stem injection) and non-chemical herbicide application. Based on the monitoring during the past years it seems that stem injection leads best to eradication of Asian knotweed. But this method cannot be applied yet because it is not in the directions for use. Next to optimising successful control methods, prevention of spreading of the knotweed via transport of soil and mowing machines is important. A national policy on ‘knotweed-free soil’ and guidelines for mowing can contribute to tackle the knotweed problem.

    • From risk assessment to cost-effective management of alien balsam species
    • R.S.E.W. Leuven, R. Beringen, E. Boer, H. Duistermaat, L. van Kemenade, J. Matthews, B. Ode, B. Simons, J.L.C.H. van Valkenburg & G. van der Velde
    • An inventory shows that 24 alien Impatiens species occur in Europe, among which 13 species tolerating the Dutch climate and habitat conditions. In total, 7 alien Impatiens species have already been recorded in The Netherlands. Ecological risk assessments of these species show that the Himalayan balsam (Impatiens glandulifera) is most invasive and strongly affects biodiversity and ecosystem functioning. This species is already wide spread in several European countries, including The Netherlands. Therefore, the European Commission has proposed that the Himalayan balsam should be listed as an invasive alien species of EU concern. Adopting this proposal means that competent authorities, water boards, nature conservation organisations and other stakeholders must implement appropriate measures to combat the species. Successful eradication and prevention of re-establishment of the Himalayan balsam will require a river catchment approach that combines the cooperation of all riparian land owners, support of stakeholders and participation of volunteers in management measures.

    • The impact of non-native aquatic plant species on the functioning of fen peat lakes
    • B.M.C. Grutters, W.C.E.P. Verberk & E.S. Bakker
    • In fen peat lakes, aquatic macrophytes provide food and structure to fish, waterfowl and macroinvertebrates. They can inhibit phytoplankton blooms and regulate greenhouse emissions. In a series of experiments, we tested how well non-native aquatic plants could provide such ecosystem functions, compared to native plants. We found that overall, native and non-native aquatic plants did not differ in their provisioning of ecosystem functions, despite their different evolutionary history. Instead, ecosystem functioning varied with plant identity and depended on plant traits such as whether plants were emergent or submerged, and their nitrogen and phenolics content. Many non-native plants appear well adapted to human-impacted Dutch aquatic ecosystems, so combined with the beneficial functions that they provide, non-native plants can help maintain ecosystem functioning in disturbed aquatic ecosystems in the future.

    • Crassula helmsii; from elimination to control measures
    • J.M.M. van der Loop, H.H. van Kleef, J.L.C.H. van Valkenburg, L. de Hoop, B. Ode & R.S.E.W. Leuven
    • The plant species Crassula helmsii, originating from Australia, is invasive in multiple European countries and since 1995 present in The Netherlands. The species is mostly introduced by humans, benefits from disturbed ecosystems with empty niches and is negatively affecting ecosystems by reducing water quality and out-competing native species. The total elimination of C. helmsii by for instance application of agricultural film, sod cutting, herbicides or light limitation, fails when the species is abundant, wide spread and not isolated at the infested location. Therefore, considering vegetation control –limit the abundance of the species- instead of eradication is logical. However, the most common control measures are only battling the symptoms of the species’ infestation and continuous management efforts will be necessary. A system-based approach is probably a viable option for durable and cost-effective control of the species. This method is increasing the resistance of the ecosystem against invasions of C. helmsii by reducing empty niches and manipulating succession and species’ favourable factors like nutrients. Laboratory and field experiments are currently performed to determine effectiveness of system-based approaches to control C. helmsii. Next to the control of the species, prevention of introduction and spread is also essential to reduce infestations.

    • Is the allochthonous Louisiana red swamp crayfish a serious threat to the Dutch fenland region?
    • H.F. van Dobben, J. Lamsma & H. Kampf
    • Since 2010 very high densities of the Louisiana red swamp crayfish (Procambarus clarkii) are reported in the fenland region of the southwestern Netherlands. In a local study the increase of this species coincided with a strong decrease of both aquatic vegetation, dragonflies and damselflies. Of special interest is the Green hawker (Aeschnea viridis) which is a red list species that is dependent upon the Water soldier (Statiotes aloides) for its survival. Both these species strongly and simultaneously declined, and it is highly probable that the crayfish is an important causal factor. Besides negative effects on the native flora and fauna the crayfish may also be a threat to waterworks due to its burrowing behaviour.

    • Alien species in the waters along the Dutch coast
    • A. Gittenberger & M. Rensing
    • Nowadays alien species play an distinct role in Dutch ecosystems. Although alien species are locally dominating ecosystems in the more inland marine waters of The Netherlands, the number of aliens that is abundant in the North Sea is relatively low. The American razor clam forms an exception to the rule as it is very abundant in the North Sea and may at least partly be responsible for the decline of the populations of several native razor clam species. Although marine alien species have certainly had distinct impacts on the ecosystems in especially the Dutch Delta and the Dutch Wadden Sea by competing with the local flora and fauna, there are no examples yet of marine native species that have gone extinct in The Netherlands, because of an alien species. Therefore the number of species, i.e. the biodiversity, has risen along the Dutch coast over the years with the arrival of aliens coming from other continents.