De Levende Natuur nummer 5 van 2013 (English summary)

Caring for invertebrates in nature conservation policy

M.F. Wallis de Vries

Invertebrates represent 65% of the known biodiversity in the Netherlands, but despite this large share, their significance in nature conservation policy is of minor importance compared to vertebrates. The large number of species presents a major challenge to include invertebrates as targets for policy, although promising attempts have been made. Among these is the list of typical species for Natura 2000 Annex I habitats, but its practical significance is limited. A further obstacle is the lack of knowledge on distribution, population trends and ecology for many species, with the exception of butterflies, dragonflies and grasshoppers.

Still, there are good reasons to give higher priority to invertebrates in nature conservation policy. First, there is the large number of threatened species, including a substantial number of well-studied species. Second, the essential role of invertebrates in ecosystem functioning and the delivering of ecosystem services warrants a greater care for invertebrates. Third, their short life cycle and variability in population size makes them potentially powerful indicators of environmental change at local and global scales. Good examples of indicators have been developed for butterflies in particular. In the context of nature conservation, invertebrates have a clear added value in highlighting specific features at the scales of both the landscape and microhabitats. Finally, charismatic groups such as butterflies and dragonflies have a growing value in generating public support for nature conservation.

Selecting a practical and ecologically meaningful set of target invertebrates for nature conservation remains a great challenge, but the rapidly growing evidence base holds great promise for a more important role of invertebrates in future policy!

‘1000-soortendagen’ mark the importance of invertebrates

E.O. Colijn

During the last five years the European Invertebrate Survey - the Netherlands conducted several large-scale biodiversity surveys in various areas. This paper presents a summary and analysis of the results. The surveys confirm the fact that invertebrates make up a large part of Dutch biodiversity but also uncover the lack of species specialists for various taxonomic groups.

Spiders in a spatial and evolutionary context of nature management

D. Bonte, K. Lambeets & M. Vandegehuchte

Spiders are well recognized bio-indicators for the evaluation of environmental change and nature management strategies. Because of their tight link with local biotic and abiotic factors, every change in environmental conditions will lead to shifts in species composition and diversity. Only by applying trait based approaches, a thorough understanding of the ongoing processes and vulnerability can be achieved. We demonstrate this concept for spider communities in dynamic coastal and riverine habitats with species inhabiting stressed habitats being large sized, slow developing, low mobile and specialist species. Increasing environmental heterogeneity will maximize species diversity, but the presence of species additionally depends on the landscape composition and evolutionary responses in dispersal ability. While species distribution patterns depend on the species long distance dispersal ability by ballooning, local population dynamics are more affected by short distance movements. Dispersal abilities are additionally constrained in already longtime isolation populations. Finally, spiders are as top predators sensitive to changes in prey composition and may serve as indicators for food web perturbations. We demonstrate that because of bottom-up effects, changes in plant genotypic composition can cascade up to the highest trophic levels and affect the abundance and species composition of spiders.

Hoverflies (Diptera: Syrphidae) love old grown forests

W. van Steenis & M. Reemer

Dutch forests are becoming older and larger. As a consequence Syrphidae with larvae living in trees (saproxylic species) are doing well. No species within this ecological group are decreasing, instead many species are increasing. Some species presumed extinct are now more and more recorded (Mallota fuciformis and Chalcosyrphus piger); these species benefit from the current forest management. Forests are allowed to grow older and old and dead trees are left in the forest.

However, trends in non-saproxylic forest species are not so positive. Several species with larvae living in herbaceous plants or living on aphids are seriously declining. This might be correlated with fewer herbs and flowers and a more uniform microclimate in the Dutch forests, possibly related with a surplus of nitrogen. Management of forest edges and small clearings might be helpful for these species.

Special attention should be given to Psarus abdominalis; this species is extinct in The Netherlands, possibly due to vanishing coppice management.

Dead wood beetles

The forest cover of Flanders and the Netherlands has been very low for centuries. Remaining forests were intensively managed and old trees and dead wood became very scarce. The biodiversity associated with these elements makes up an important part of the overall forest biodiversity, and was probably to a large extent lost over time. Only during the last decades, dead wood and old trees are progressively reintegrated in the forest management, possibly to reach now their highest level over the last 500-1000 years. The ability of related beetle species to recolonise the newly available habitat is strongly determined by limitations in their dispersal and recruitment ability. We tried to evaluate the current status for saproxylic beetles by means of several indicator species, and a number of intensive field  inventories in sites with high potential. Our results showed remarkably good results for the saproxylic beetle diversity of our forests and indicate a progressive recolonisation process. This confirms and justifies the efforts for conservation of dead wood and habitat trees in modern forest management. We conclude with some practical recommendations for conservation management.

Cucujus cinnaberinus: a species from the Habitat Directive gives indications for forest management

J. Noordijk, E.O. Colijn, A.P.J.A. Teunissen & C.F.P. Vendrig

In 2012, the beetle Cucujus cinnaberinus was found for the first time in The Netherlands, in a forest with abundant fresh dead wood in the southern part of the country. The species was later also found in two other nearby nature reserves. This species is protected on a European level by the Habitat Directive. In this paper, we describe its ecological requirements, with special references to forest management. Forest managers should be very careful with recently died trees as these represent the habitat of the larvae and adults in moist forests. The trees should never be removed, and even the removal of branches should not be done, since this affects the favourable moist micro-climate under the bark of the whole tree. Large quantities of fresh dead trees caused by e.g. wind throws or a rise in the water level can attract the beetle to new areas. When the dead wood becomes old, the beetle has to rely on the normal rate of tree mortality, which might not be sufficient in many forests, and adding stems of trees (preferably poplar) from the surrounding area might enhance the population. It is recommended to exclude several tree stands in all forest areas from management (possibly after initial cuttings to promote a varied age build-up of the trees to begin with) to promote the development of more old forests. Since sufficient quantities of fresh dead wood are only occasionally created by catastrophic events, C. cinnaberinus needs to be managed on a regional scale. Preserving dead wood in all forests and defragmentation of separate forest areas in the south of The Netherlands are priorities for its conservation. Moist forests are not rare in the southern part of The Netherlands and the owners should be aware of the potential presence of this protected beetle.

The intimate relationship between tree species and earthworms

S. Schelfhout, A. De Schrijver, L. Vesterdal, J. Mertens & K. Verheyen

Earthworms play an important role as ecosystem engineers. After 40 years of afforestation, the earthworm populations were influenced by the soil acidifying capacities and litter quality of six different tree species. Deep-burrowing anecic earthworms were most often absent in Spruce stands, whereas in Oak and Beech the results were variable depending on the exchangeable aluminium concentration. The highest chance on anecic earthworm presence was found in Ash, Maple and Lime stands.

The influence of soil organisms on plant growth and nature restoration

E.P. Brinkman & W.H. van der Putten

Soil organisms are mostly neglected in terms of conservation policy. However, in recent years it has become more apparent that they serve an important role in community processes. Therefore, in nature restoration projects, it should be considered what the role of soil organisms is in that specific system. When the topsoil including the main part of the soil community is removed, it may be necessary not only to bring back seeds, but also soil organisms from a related target community to stimulate the development of a specific vegetation type.

Without death, less life – more chances for carrion fauna in nature conservation

E.O. Colijn & B. Beekers

The importance of dead wood for biodiversity is generally understood and accepted. For dead animal matter this is not the case, although various vertebrate carrion feeders and a large number of invertebrates live of or in this mini-ecosystem. This paper presents a review of the Dutch emotional, legal and ecological framework relating to carrion management in nature reserves and hopes to contribute to the acceptance of dead animals in nature in The Netherlands.

Grazing intensity and insect diversity of heathlands

J. Noordijk, E.O. Colijn, J.T. Smit, K. Veling & M.F. Wallis de Vries

Grazing as a management tool for biodiversity conservation in heathlands is widely applied in The Netherlands. It is a relative cheap method that maintains an ‘open’ landscape and creates vegetation mosaics. In this article, we describe a field survey on the relation between grazing intensity (of cattle and/or sheep) and species richness of characteristic heathland insects of the following groups: grasshoppers, the cicadelid Ulopa reticulata, butterflies, hoverflies, bees and ants. Ten plots on dry and six on wet heathlands were selected, and the plots could be categorised into four classes: ungrazed, extensively grazed, intensively grazed and very intensively grazed. Species diversity increased significantly with an increasing grazing pressure. In ungrazed plots only few characteristic species could be found and only one hoverfly species was exclusively found here. In intensively grazed plots the number of characteristic insects was high. In the very intensively grazed plots in wet heathland, the total number of observed species was even higher, because during three months in summer the plot was excluded from grazing to allow flowers (amongst others Gentiana pneumonanthe) to thrive. It is no surprise that heathland insects respond very positively to (intensive) grazing. Heathlands are created and maintained for centuries by grazing and other agricultural activities. The characteristic fauna has developed under these circumstances; a heathland without grazers is therefore an incomplete system with few chances for characteristic biodiversity.

Large ungulate grazing – a curse or a blessing for grasshopper communities?

M.J.J. Schrama & A.L.D. van der Plas

In northwestern Europe, large ungulates are often used for the benefit of nature conservation. Grazers have often been shown to have positive effects on plant species richness, but their effects on insects are less well known. Here, we studied the effects of large grazers on grasshopper communities, by surveying grasshopper communities inside and outside exclosures in six grazed nature areas in the Netherlands. We found that overall, grazers reduce grasshopper species richness. This was mainly because katydids (Tettigoniidae) were only found within the exlosures, while the richness of other grasshoppers (Acrididae and Tetrigidae) was not affected by grazers. However, the two declining (or threatened) species found in this study, Chortippus montanus and Oedipoda caerulescens,had higher abundances outside the exclosures. The same was true for the small species of grasshoppers. This might be caused by the higher quality of the available food plants, or because of the higher daytime temperatures in short vegetation. Concluding, we suggest that grazing management is a suitable tool for the conservation of rare and declining grasshopper species.

Ant communities of heathlands

R. Versluijs, J.J. Vogels & C.G.E. van Noordwijk

In spite of large scale restoration efforts in heathlands over the past decades, many characteristic heathland arthropod species have continued to decline. Restoration efforts have focused on nutrient-poor heather vegetation while heathland landscapes historically consisted of many land-use forms and vegetation types. In this article we investigate the effects of different forms of heathland management on ants and we explore the driving factors shaping ant communities in heathlands by matching species life-cycles to habitat characteristics.

For ants the main factors determining habitat suitability are related to the openness of the vegetation (affecting the microclimate), the presence of a well-developed litter layer, the degree of disturbance and the availability of food sources. Due to the different demands of each ant species, there is no ‘golden management rule’ serving all heathland ant species. Unmanaged heather vegetations were most species-rich, however typical thermopile ant-species benefit form more open heather vegetations which exists due to grazing or sod-cutting. Overall ant abundance was highest in fallow fields and some ant species were more or less restricted to these sites. We conclude that effective heathland conservation requires a management vision at the landscape scale, incorporating variation in vegetation type and land-use form to ensure conservation of a variety of structures and habitats (open sand, litter, warm and cool habitats, greatly disturbed and undisturbed situations).These results can be extrapolated to a wider spectrum of species as many arthropod species have similar habitat requirements (microclimate, food availability etc.), some plant and butterfly species need ants to complete their life-cycle and several threatened heathland birds rely on ants as their main food source.

Can arthropods benefit from green hay transfer?

C.G.E. van Noordwijk & A. Klimkowska

Application of hay from species-rich donor sites is widely accepted as a measure to overcome dispersal bottlenecks for vascular plants after top-soil removal on former arable land aimed at restoring nutrient poor grasslands. Many invertebrates that are characteristic of nutrient poor grasslands also have poor dispersal abilities, and hence, have great difficulty colonizing restored sites. It seems possible to introduce arthropod species living in standing vegetation simultaneously with the plant propagules through fresh hay transfer. We describe an experiment testing which invertebrate taxa are able to survive in the hay during mowing and transport. Two different mowing and transport techniques were compared to determine how mechanical versus manual mowing influenced survival rates. Results showed that most invertebrate taxa living in standing vegetation can survive in mown and transported fresh hay. However, densities drastically declined after mowing and again after transport and the survival rates differed between taxonomic groups. Little difference was found between the two mowing techniques. However, the manual transport technique was six times more efficient in terms of arthropod transfer (densities) than the mechanical hay collection and transport. This indicates that the transport technique and the time interval between mowing, collection and transport have a major impact on the effectiveness of transport of invertebrates with fresh hay. After transport, meeting the food, shelter and microclimatic demands is vital for survival of invertebrates in a restored site. Therefore, application of fresh hay directly after topsoil removal, when there is little vegetation cover, is not suitable for most invertebrate species. This is however, the optimal timing for vascular plants, making it difficult to aid the colonisation and re-establishment of both plants and invertebrates with a single hay transfer event. A second hay transfer event, two to three years after the first, can be effective for invertebrates if performed with appropriate methods. It may however be cheaper, more effective and less disturbing to collect invertebrates with sweep nets and transfer them manually.

Missing links in the food chain of dune grasslands?

B. Wouters & H.H. van Oosten

Faunal diversity in dune grasslands (Natura2000 habitat-type H2130) along the Dutch coast is threatened by encroachment of nitrophilic grasses. To re-establish open and warm dune grasslands site, managers deploy intensive management efforts. However, in spite of successfully decreasing vegetation biomass, positive effects on animals are scarce. We investigate the relation between management, effects on invertebrates and lastly, whether changes in invertebrate fauna could affect characteristic insectivorous birds as the Northern Wheatear (Oenanthe oenanthe) whose diet we determined by filming feeding parents at the nest. We found that especially Elateridae, Scarabeidae and Acrididae are often fed food items. To be able to optimize management we investigated if and how occurrence of these invertebrates is influenced by management. We found that grazing by large ungulates recreates short grown dune grasslands with short yet closed vegetation with few sandy patches. Temperatures in grazed grasslands are warmer than in encroached situations, yet lower than in sandy open grasslands. It appears that development time of grasshopper eggs in grazed grasslands is two weeks shorter than in encroached grasslands, but still almost one month longer than in sandy grasslands. Recreating blow-outs appears to be an important management tool to increase invertebrate diversity on which insectivorous birds as Meadow Pipits (Anthus pratensis) and Northern Wheatears depend. Even though management does not solve all fauna bottlenecks, it remains necessary to prevent vegetation succession to further affect open and dry dune grasslands, and to increase faunal diversity especially by creating blow-outs. Possible ways to optimise management are discussed.