Brown roofs for invertebrates
substrate. Other materials such as pulverised fuel ash (PFA) are a declining national resource
that is known to support an extremely important invertebrate fauna (Harvey 1999). There is the
potential to use this material on brown roofs. The use of chalky material is also likely to have
high potential, and could help some invertebrate species associated with chalk grassland. Surface
rubble, pieces of rock and dead wood will provide shelter and a niche for species that prefer
shady damp conditions, or which are active at night.
• The topography of the brown roof. This should be varied, with hollows, mounds and south-
facing banks to provide different substrate depths, physical diversity and hydrology. This should
lead to the development of vegetation with a varied species composition and structure, with a
resultant associated invertebrate biodiversity.
• Plant species. Many invertebrate species are associated with a specific plant or range of plants,
or are predators that prey on these invertebrates. Important forage plants include those in the
Apiaceae (carrot family), Asteraceae (daisy family), Fabaceae (pea family), Lamiaceae (dead-
nettle family) and Scrophulariaceae (figwort family). Other invertebrate species are closely
associated with other plant species. Examples of plants that would be especially valuable on
brown roofs include Carrot Daucus carota, mugworts Artemesia spp., thistles Cirsium arvense.
C. vulgare, Knapweed Centaurea nigra, yellow composites Crepis spp., Picris spp., ragworts
Senecio spp., vetches such as Fodder Vetch Vicia villosa. Broad-leaved Everlasting-pea Lathyrus
latifolius, Bird's-foot-trefoil Lotus corniculatus, Red Clover Trifolium pratense, Black
Horehound Ballota nigra, Red Dead-nettle Lamium purpureum. Red Bartsia Odontites verna,
Mignonette Reseda lutea, Weld R. luteola. Many of these species might establish naturally, but
some might be better seeded - for example Carrot, Knapweed, Bird's-foot-trefoil, Red Clover,
Red Bartsia and Reseda. Scrub species in drought-stressed conditions that would provide dead
stems for stem nesting species, as well as valuable forage, would be bramble Rubus fruticosus
agg. and wild rose Rosa spp.
• Management. Although the availability of specific plants and the resources they provide is a
key factor for many invertebrate species, the structural characteristics of habitats are also very
important. A varied sward and mosaic of vegetation heights, a continuity throughout the season
of various leaf, stem, bud, seed, nectar and pollen resources and the availability of over-wintering
dead stems and seed heads are all essential for many species. Management of roofs to ensure
'tidy' and controlled vegetation would be extremely detrimental to its associated biodiversity.
Management should be minimal, sufficient to maintain a proportion of bare ground and prevent
scrub invasion such as Buddleia. In mineral deficient and drought-stressed conditions, the
need to control vegetation should not become a problem for many years, when occasional
disturbance to re-establish bare ground will be beneficial. The aim should be to provide
continuity through the summer and winter of forage, stems, fruits and seeds, to enable a wide
diversity of species to feed and over winter successfully. Any form of regular management that
removes a significant proportion of these resources will be very harmful to the associated
invertebrate fauna. Cutting will be destructive unless it is done on small areas on a long rotational
basis. Physical removal of establishing scrub, such as Buddleia, will be the best option and will
actively promote the creation of valuable bare ground. However a certain amount of drought-
stressed bramble and rose scrub would be important as a stem-nesting resource.
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Essex Naturalist (New Series) 21 (2004)