Reedbed habitat audit

Reedbeds are wetlands dominated by stands of common reed Phragmites australis, where the water table is at or above ground level for most of the year. For the purposes of this audit, reedbeds are identified as stands (or continuous belts) of common reed which exceed 0.5 ha in extent.

Reedbeds occur at the margins of lakes, pools, rivers or reservoirs in water that is less than 1 metre deep. Due to the dominance of common reed, reedbeds are often botanically poor (although they can support a variety of rare wetland plants) but are very rich in invertebrates. There are a number of bird species that are closely associated with reedbeds.

Despite covering only a tiny proportion of London's surface area, reedbeds are of special nature conservation value. By their very nature most reedbeds are uncommon and transient features of the natural landscape. The right conditions for reedbed establishment occur infrequently. Where reedbeds do become established they are prone to succession to willow scrub and wet woodland unless there is some constraining factor. Drainage and development of wetlands have exacerbated the natural scarcity of this habitat.Although reedbeds are naturally scarce, there are many animal species which are wholly dependent upon this habitat. In London these include reed warbler, water rail, and the fen wainscot moth. At least five other species of moth in London are dependent upon reed as a larval foodplant.

The major threats to reedbeds are drainage and lowering of water tables; lack of, or inappropriate management; and loss to development. Succession is not usually a problem associated with tidal reedbeds in the Thames, as regular inundation with brackish water usually prevents the establishment of scrub. One of the main threats to tidal reedbeds is dredging of the main river channel nearby, which may result in the erosion of the accumulated silt upon which the reedbed is established.

The scope for the restoration of reedbeds in London is perhaps limited considering the lack of extensive areas of undeveloped riverside or semi-natural lakeside. However, there are considerable opportunities for the creation of reedbeds as part of flood defence and river enhancement schemes and gravel pit restoration. Furthermore, as the amount of dredging required on the Thames declines or is better targeted as a result of fewer movements of large ships, there are possibilities for re-establishing tidal reedbeds on exposed mud-banks at the rivers edge.

Further opportunities arise as a result of the ability of reedbeds to attenuate storm-water run-off and remove certain pollutants. There is a growing interest in incorporating constructed reedbeds into surface water and grey water drainage systems for this purpose. These could result in the creation of relatively large reedbeds, which may provide valuable wildlife habitat.