Brown roofs for invertebrates
PETER HARVEY
32 Lodge Lane, Grays, Essex RM16 2YP
Abstract
The potential value of suitably designed brown roofs as replacement invertebrate habitat is discussed.
Habitat features that should be incorporated into their design are described and some examples of
species that might benefit are given. The need for long-term study to establish their real benefit is
required.
Introduction
Dry grassland and 'waste ground' postindustrial habitats have a known interest for large and diverse
invertebrate assemblages, and these assemblages can assume regional and national significance
(e.g. Harvey 2000a); "The Thames Estuary brown field sites are the. new lowland heaths and.
flower-rich meadows" (Jones 2003). There is enormous development pressure on virtually all
open space with nature conservation significance in the East Thames Corridor, where the 'Thames
Gateway' initiative threatens wildlife habitats and 'brownfield' sites are especially vulnerable.
Amenity management, the 'tidying up1 of habitats and the landscaping and loss of open areas to
tree planting all represent additional threats to the populations of rare and scarce species found in
the region.
The best brownfield sites have, or contain significant areas that have, been abandoned for significant
lengths of time, often 10-20 years or more. If development of these sites must go ahead, then
mitigation is strongly recommended, in the form of provision of alternative habitat within a viable
timescale to maintain continuity of populations and with the use in urban situations of suitably
designed brown roofs.
Green roofs are those that are intentionally vegetated to some degree. This can include roof-top
gardens, grassy swards, short turf, or a scattering of mosses and lichens. Brown roofs refer to roofs
specifically used in mitigation for the loss of brownfield land. However although research in
Switzerland shows that these can be important for rare invertebrates, brown roofs in this country
have not normally been designed with invertebrates in mind.
The use of brown roofs incorporated into developments may represent a crucial way of conserving
this fauna, especially in east London, where otherwise virtually no habitat is likely to remain. There
is also a good case for their consideration in any developments that take place on 'brownfield' or
post-mineral extraction sites in Essex, especially where these are in the vicinity of Colchester,
Braintree, Chelmsford, Dunmow, Bishops Stortford, Halstead, Harwich. Maldon and other major
development areas. The use of brown roofs as replacement habitat for brownfield and 'wasteground'
habitats needs to take account of the features these habitats contain that result in their importance
to populations of rare and scarce species.
Key features of brownfield and dry grassland habitat
One of the main reasons for the invertebrate importance of some dry grassland, post-industrial or
'waste ground' sites is the combination of otherwise rare ecological features that they contain -
Essex Naturalist (New Series) 21 (2004)
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