Invertebrate habitat creation and monitoring

Under the heading of Achieving Sustainable Development, Paragraph 17 of the National Planning Policy Framework sets out twelve core land-use planning principles that underpin both plan-making and decision-taking. One of these is to ‘encourage the effective use of land by reusing land that has been previously developed (brownfield land), provided that it is not of high environmental value’. Understandably, there is increasing pressure to develop brownfield sites. However, some of these are amongst our most important sites for wildlife, and in particular, invertebrates.

Canvey Wick is one such example, which in 2005 was notified a SSSI for its outstanding assemblage of invertebrates associated with open mosaic habitat. At this former oil refinery site in Essex, extensive areas of open mosaic habitat have developed on the sandy soils. Buglife have reported over 1,400 species of invertebrates at the site, including 30 Red Data Book species and three species previously thought extinct in Britain. Elsewhere, in and around Peterborough there has been a rich industrial heritage, especially in the manufacture of bricks, which has resulted in the establishment of significant areas of open mosaic habitat. One such area is Dogsthorpe Star Pit that is notified as a SSSI chiefly for its aquatic invertebrate fauna.

Working with developers

BSG Ecology has been advising master developer O&H Hampton Ltd on ecological issues over the last 10 years at Peterborough, undertaking survey, assessment and mitigation in the delivery of sustainable development projects across large areas of south Peterborough. As master developer O&H Hampton retain ownership and management responsibility for large areas of land in Peterborough of high biodiversity value including Orton Pit SSSI/SAC and since the early 1990’s the company has supported the maintenance of Orton Pit and implemented a range of work associated with planning consents that has benefitted species and habitats within the green infrastructure around southern Peterborough. In spring 2007 O&H Hampton supported by BSG Ecology set aside a 2 ha demonstration site for the creation of brownfield / open mosaic habitat for invertebrates, the approach to habitat creation and the design of the demonstration site was led by Dr Peter Shepherd and was informed by the character of habitats within the wider area of the former clay pits and publications on brownfield habitat characteristics. In 2014, BSG Ecology keen to understand how the demonstration site had developed, commissioned Buglife to undertake an invertebrate survey. This article summarises the results of this study so that we might understand more about restoration and habitat creation techniques for open mosaic habitats for invertebrates on brownfield sites.

Background to the Project

The preparatory works that took place in 2007 involved the spreading of inert materials, including brick rubble (whole or part bricks and crushed rubble), sand and gravel, concrete, and sectioned logs of felled trees upon bare clay subsoil in the corner of one of the former clay pits. A decision was taken to leave the site to colonise naturally (non-intervention management), and over the last eight years an open habitat mosaic has developed which includes embryonic species-rich grassland interspersed with scrub (bramble Rubus fruticosus agg., gorse Ulex europaeus and hawthorn Crataegus monogyna) and patches of bare ground. A strip of tall, semi-mature trees provides shade and shelter to the west of the demonstration site. Many valuable flower species for pollinators are present, including wild carrot Daucus carota, fleabane Pulicaria dysenterica, common ragwort Senecio jacobaea, slender bird’s-foot trefoil Lotus glaber, teasel Dipsacus fullonum, creeping thistle Cirsium arvense and white clover Trifolium repens and red clover T. pratense. Soil mounds and piles of dead wood may also provide suitable sheltering places for wintering invertebrates.

Field Survey Approach

Buglife undertook a suite of surveys designed to capture the greatest diversity of invertebrates likely to be found in association with the open mosaic habitats present at the demonstration site within the resources available to them for the project. Visits took place on 11 separate occasions between May and October 2014 to sample invertebrates over a typical 2-3 hour period, during which reasonably fine weather could be expected. Techniques employed included sweeping and spot capture with a long-handled insect net, sweeping with a sweep net, visual observation, and turning over logs and rubble. Two sets of five pitfall traps were set in the open habitat on two occasions. Moth trapping involved running a Skinner trap with a 125w mercury vapour bulb between dusk and midnight on three occasions. Surveys were conducted by experienced entomologists including Steven Falk, Sarah Henshall, Alan Stubbs, Jamie Robins, Chris Kirby-Lambert and Buglife volunteers (during moth trapping).

Findings

The surveys revealed the presence of 403 invertebrate species. Of these the flies (168 species) and beetles (79 species) were the most numerous, followed closely by the collective group of bees, ants and wasps (48 species). Three Species of Principal Importance (Section 41 NERC Act), one Nationally Endangered (Red Data Book (RDB) 1), one Nationally Rare (RDB3) and 13 Nationally Scarce species were recorded. One species, the ‘true’ bug Stictopleurus punctatonervosus, was also recorded that was formerly considered extinct but is now spreading across southern England.

It was interesting to observe that many of the more notable species found at the site are associated with substrates that had been recreated at the demonstration site, such as Didineis lunicornis and Odynerus melanocephalus, both nationally scarce wasps whose nests are constructed in sparsely vegetated dry clay soils. Also, a number of other nationally scarce species were closely associated with the vegetation that has been allowed to establish on site, providing important nectar and pollen for species such as Ampedus quercicola a click beetle that feeds on hawthorn flowers as an adult, and Myopites inulaedyssenterica a rare (RDB3) picture-winged fly with larvae that develop in the flowerheads of fleabane. Furthermore, the importation of timber had clearly provided opportunities for a fauna associated with decaying wood and associated fungal fruiting bodies, such as the nationally scarce cramp-ball fungus weevil Platyrhinus resinosus a species associated with cramp-ball fungus Daldinia concentrica which was found growing on decaying ash Fraxinus excelsior.

To provide a more meaningful understanding of how invertebrate assemblages at the demonstration site are organised, the data were entered into The Invertebrate Species-habitats Information System (ISIS). This is a tool developed by Natural England with the primary aim being to undertake common standards monitoring of Sites of Special Scientific Importance (SSSI) (i.e. to monitor the condition of invertebrate assemblages). Sites are scored based on the invertebrate assemblage types present, and their conservation value within a given context. The output of the ISIS analysis was that the site supported the Specific Assemblage Type, ‘rich flower resource’ in favourable condition, indicating that the plant communities at the demonstration site are of excellent quality for invertebrates. Furthermore, the Broad Assemblage Type, ‘unshaded early successional mosaic’ was also well represented, with favourable condition assigned this assemblage type as well, owing to a high number of scarce species associated with this assemblage type.

Conclusion and Next Steps

The research showed that the habitat creation that took place in 2007 had laid the foundations for an area of land that is rich in both plants and invertebrates, and numerous scarce species are present. What is most revealing is the short period of time over which the invertebrate fauna has colonised the demonstration site, and also that this has established through a lack of site management (non-intervention approach). What is not known however, is at what stage will the invertebrate assemblage reach maximum diversity, and support the greatest number of scarce species? It is well known that prolonged periods of neglect can cause species-rich habitats to be eventually replaced by coarse grassland, scrub and eventually secondary woodland; habitats that are more common-place and generally hold less interest than the conditions currently found in the demonstration site. It would be highly rewarding to continue this research by re-surveying the site in another five years following non-intervention to see whether the balance has shifted and species diversity is starting to decline, at which stage periodical mechanical disturbance would be the most appropriate intervention to return the favourable condition of the site for invertebrate assemblages of open mosaic habitats. We are also considering if there are further habitats that could be easily created within the demonstration site that could further enhance the invertebrate value of this area.

For further information on our brownfield invertebrate research, please contact Jim Fairclough – 01433 651869

Top photographs: Right – Black-headed mason wasp Odynerus Melanocephalus ; Left – SphaerophoriaTaeniata– photo taken by Steven Falk Invertebrate Specialist at Buglife