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Brownfields may sound a bit dull, but they aren’t if you’re a hard-pressed invertebrate, having to fit its lifestyle around human activity. Brownfield sites can have as many rare invertebrate species as ancient woodlands, and many act as important ‘reservoirs’ of wildlife.
On the most wildlife-rich brownfield sites, cycles of disturbance and abandonment combined with low nutrient soils (no one bothers to fertilise them…), both give rise to a wide variety of habitats, patterns of water temporarily ebbing and flowing and a mini-ark of plant species. Many invertebrates have complex life-cycles, needing different things at different stages, so they often require two or more habitats close to each other – a ‘mosaic’ of habitats rather than miles and miles of the same.
Brownfield sites are one of these precious mosaics in the wider landscape, providing habitat variety that is rare in the agricultural countryside.
Many flying insects need to forage to gather nectar and pollen. The size and nature of the foraging area needed differs from one species to another, as some forage on many different flowers, while others are choosier.
The low nutrient content of many brownfield sites results in many plants thriving together, as fast growing species are unable to grab the nutrients they need to dominate. The thin, dry soils also result in thirsty plants putting more effort into flowering to ensure they can set seed to survive another year. This also increases the nectar and pollen available to tempt the pollinators.
The invertebrates attracted by the brownfield plants and habitats attract other invertebrates and small mammals, even amphibians and reptiles such as frogs and lizards, and this in turn attracts predators. Open, flower-rich vegetation, grassland and scrub all provide opportunities for different predators.
Another feature of many brownfield sites is open, bare ground. This warms up rapidly in sunshine, so is good for basking on. It is used by burrowing and ground nesting invertebrates, and provides a foraging area for visual predators (creatures that stalk their prey by eye rather than by smell, vibration or sound).
Plant-eating invertebrates often live inside leaves, stems, flower heads or seeds and overwinter in these places, under logs or stones, or in ground litter. For these species it is critical that their over-wintering sites are undisturbed. The lack of interest most people show in brownfield sites is precisely what makes them so appealing for these invertebrates.
Brownfield sites provide ‘surrogate’ habitats for species that would be found in other habitats if it were not for human interference.
The intensification of farming has led to the loss of flower-rich grasslands from the countryside, leaving brownfield sites as the last refuge for certain species. Car parks, warehouses, shopping centres, housing and flood defences, to name just a few, have left many bare-ground species with nowhere to go but brownfields.
If no one’s interested in brownfield sites, why are they under threat?
Well… various people are interested in them, but nearly always (from a bug’s point of view) for the wrong reasons.
To reduce urban sprawl, government policy adopts a ‘brownfield first’ approach, targeting new developments on available sites within urban areas. This is a good idea in principle, but it doesn’t take wildlife into account. The National Planning Policy Framework allows for the protection of biodiversity, even on brownfield sites, but even so they are often seen as ‘useless’ areas attracting antisocial behaviour (such as fly-tipping).
None of this helps in efforts to conserve them. Yet for many of these sites there is no reason why they cannot provide a valuable open space for the local community, with some thoughtful planning and awareness raising. Conversely, the green spaces that surround towns and cities that have strong protection from development (both through the planning process and through public opinion) are often products of our recent agricultural history, and have relatively little value for wildlife.
Mismanagement can also be a threat. Turning a brownfield into ‘pretty’ greenspace through importation of topsoil, seeding grassland and planting ornamental trees, or ‘green-washing’ as it is sometimes known, can be as devastating to brownfield wildlife as a housing development.
Buglife is working hard to address the problems confronting brownfield biodiversity, through developing brownfield habitat management advice and a strategy for the conservation of our most important brownfields.
We hope to change public opinion on the value of the sites and encourage a ‘biodiversity first’ approach to planning, where sites of low value for wildlife, whether brownfield or greenfield, are prioritised for development.
We also want to see developments that do go ahead on brownfield sites incorporating areas of brownfield habitat and wildlife-friendly designs such as brown roofs and green walls.