Untangling the complexities of open mosaic habitat creation and management

The SRI are celebrating another PhD completion and another successful collaborative applied research project. Having completed his thesis earlier this year and successfully defended it during his viva, Dr James McGill has now graduated and his thesis is available online.

Figure 1. Mosaic habitat at Canvey Wick SSSI. The blend of anthropogenic construction and renaturing by recolonization on brownfield sites can create a mosaic of habitats that can support nationally important populations of wildlife. Image © Stuart Connop

James carried out a study investigating Open Mosaic Habitat management and creation. Open Mosaic Habitat (on Previously Developed Land) is a term that has been coined to characterise the biodiversity-rich habitat that can sometimes be found on brownfield (post-industrial) sites in the UK. The East Thames Corridor, where James carried out his studies, and where the UEL campuses sit, is particularly important for this type of habitat. Many nationally rare and scarce species utilise these sites as a proxy habitat due to the loss and fragmentation of the habitats that they would have previously been associated with in the region (typically Thames Terrace Grasslands, and grazing marshes). Some brownfield sites in the region can support comparable invertebrate diversity to semi-natural early successional habitats. The brownfield sites are, however, under enormous pressure for redevelopment being prioritised for development in the National Planning Policy Framework to help meet the huge demand for housing and infrastructure.

Figure 2. Redevelopment of a brownfield site for housing. Brownfield sites are under enormous pressure for redevelopment in the south east of the UK. This brings with it the risk of loss of the unique wildlife assemblages that can develop on some of these sites. Image © Stuart Connop

If the nationally important biodiversity associated with these sites is to be protected and the populations expanded, it is vital that we understand more about Open Mosaic Habitat. Critical in relation to this objective are:

• developing an understanding of how to manage the Open Mosaic Habitat on the most valuable brownfield sites once they are recognised and designated for their nature conservation importance;
  

and

• exploring how an understanding of the ecological functionality of Open Mosaic Habitats can be applied to other habitats to enhance their value for diverse species assemblages.
  

This project was developed as a CASE PhD Studentship with Buglife (the Invertebrate Conservation Trust) in response to the need for information to assist with management of brownfields protected for nature conservation, and from the lack of evidence about the effectiveness of brownfield mosaic habitat creation. The Royal Society for the Protection of Birds (RSPB) and the Land Trust also partnered the project.

Figure 3. The streaked bombardier beetle (Brachinus sclopeta). One of many nationally threatened conservation priority species that can be found on brownfield sites in the East Thames Corridor. Image © Stuart Connop

James’ study began to tackle these knowledge gaps. Working on a range of sites in the region (including Canvey Wick SSSI, Hadleigh Park and Rainham Marshes Nature Reserve) James monitored the effects of a variety of habitat management and creation techniques on the invertebrate populations of these sites. This included: management interventions at Canvey Wick (a brownfield nature reserve) focused on resetting an early successional stage habitat; mosaic habitat creation by substrate addition in unmanaged grassland; and placement of artificial aculeate nests on green roofs in London.

Figure 4. Mosaic habitat creation in an area of rank grassland. Five tonne mounds were created  and monitored to compare the performance of two substrate types – Thanet sand and recycled builders sand. Monitoring was carried out to asses the habitat value of the mounds for for bees, wasps, beetles and spiders as part of the PhD studies. Image © Stuart Connop

Detailed descriptions of James’ experimental design, results and conclusions can be found in his thesis. A few highlight include:

• Scrub clearance at Canvey Wick produced distinct communities of stenotopic invertebrates immediately after management, and one year later. Trait-based analysis showed that staphylinids and spiders were larger at undisturbed plots, dispersal traits for carabids and spiders were linked to disturbance, and trophic shifts for all three groups.
  

• In species-poor grassland at Canvey Wick, stenotopic beetles particularly benefitted from scraping, whereas stenotopic and generalist spiders were more abundant after excavator disturbance, and at unmanaged plots. Carabids and staphylinids were larger at undisturbed plots, although treatment responses in leg and eye morphology were not shared.
  

• Substrate addition in unmanaged grassland on clayish soils in south Essex benefitted nesting aculeate Hymenoptera, particularly in the first year. Stenotopic early successional beetles and spiders were more abundant in the second year, although species composition was similar to the grassland.
  

• Cavity nesting aculeate Hymenoptera were reared from biodiverse and unvegetated roofs in London. Although most sites were not colonised, and substrate nests were unsuccessful, some cavity nesting occurred demonstrating the value of adding such habitats to green roofs. Longer-term study is required to investigate whether greater colonisation of the artificial habitats occurs after the first year of the study.

Figure 5. Artificial habitat for cavity nesting bees. Wooden blocks with different diameter holes were installed as part of an experiment to provide additional habitat resources on green roofs for bees and wasps. Image © Stuart Connop

Results were explored in relation to broader literature concerning invertebrate conservation in early successional habitats. Implications for land managers were discussed, including species turnover, habitat structure, and potential benefit to ecological networks from habitat restoration, management and creation in appropriate locations. These implications can be read in detail in the thesis, the overall message from the study was the critical importance of maintaining a range of ages of successional stages on Open Mosaic Habitat sites: a single year of plant colonisation can be enough to significantly alter assemblages on these habitats. It is hoped that James’ studies will continue and further explore the complexities of how to manage and create Open Mosaic Habitats to conserve their unique assemblages.

By Stuart Connop