Invertebrate survey at Gunpowder Park, the former Royal Ordnance Site in the Lee Valley
At the same time occasional scarification and furrowing of areas within the substrate-poor
grasslands to expose bare ground and produce a varied topography will produce valuable
microhabitats and also help prevent the loss of sparsely vegetated areas through succession. The
proportion of new grasslands that need to be subject to this form of management is unlikely to be
large - an average of 5% disturbed per year is probably more than enough to maintain the invertebrate
populations requiring this kind of habitat. This is pretty much unknown territory, but it is probably
best to aim for a proportion of disturbance in as many grasslands as feasible, so that invertebrate
populations can benefit from habitat at a landscape rather than isolated level. The areas disturbed
to expose bare ground can be small, and could either produced as a patchwork within the grasslands
or in strips or corridors, whichever would better suit landscape issues and public perception.
Additional sowing of plants such as Fodder Vetch Vicia villosa, Lucerne Medicago sativa, Carrot
Daucus carota and Parsnip Pastinaca sativa into the developing grasslands is recommended.
These plants are extremely valuable forage resources to different invertebrate species, and might
encourage colonization of the grasslands with important species recorded at the nearby Rammey
Marsh. Scarification of areas prior to sowing would be likely to improve the success of this strategy.
Where there are slopes, especially south facing, it is recommended that small areas are periodically
scraped to expose bare ground. The creation of short sections of vertical bank would also be
extremely beneficial for ground nesting aculeate Hymenoptera.
Osier Marsh
The major management problem in the Osier Marsh area will be to prevent the loss of the seasonally
exposed PFA pond edges and marsh vegetation to colonization by osier and birch, especially in dry
summers. Pulling of invading willow and osier is recommended to slow succession, but in the
longer term further mechanical work to open up areas lost to developing woodland would be highly
advantageous.
If osier and birch scrub and woodland could be removed and large enough areas of PFA substrate
exposed, then valuable open habitats would develop on the friable PFA. An existing raised area
immediately to the south at the eastern end of the western PFA pond has a somewhat heathy nature,
and a more extensive area of similar habitat would be valuable. Raised PFA in the form of mounds
and banks would provide important nesting substrate for ground nesting species. Currently this
type of habitat is restricted to a rather few upturned root plates in the open, where for example in
2003 the mining bee Andrena clarkella was seen nesting on the southern side of the western PFA
pond.
Excavated areas in exposed PFA would develop vegetation communities associated with damper
habitats, and there would be every possibility that glades of marsh orchids previously found on
PFA in the Lee Valley (Shaw 1994) might colonize or reappear. The development of more extensive
marshy vegetation, especially with plants such as Angelica, Purple Loosestrife, mint, figwort etc.
would provide additional extremely valuable invertebrate habitat.
Comfrey is an invasive plant, which can out-compete and replace existing diverse vegetation.
Although bumblebees use its flowers and the agromyzid fly Agromyza ferruginosa, a local species
that mines Symphytum, was recorded during this survey new to Essex, the plant has deep-branched
tap roots and large shading leaves and will spread rapidly and smother other vegetation, becoming
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Essex Naturalist (New Series) 21 (2004)