Securing Biodiversity in Breckland - European Commission

Grazing of Wetlands and Fluctuating Water BodiesWetland assemblages have been identified that require: Short vegetation such as provided by grazing or that require trampling and poaching withinthe wetland or at littoral margins. Other species require less disturbed tall vegetation, tall stems or litter accumulation, whichwould best be provided by very low or no grazing.For assemblages of wetland species broadly similar numbers were identified that require grazedconditions (41 priority species) compared to ungrazed (44). However, grazing sensitivity of a slightlygreater number was unknown (94). For priority species associated with littoral conditions, a similarpattern was apparent (34 species requiring grazed, 21 ungrazed, 28 unknown). The pattern forBreckland specialists was broadly similar.Wetlands with no or light grazingCryptonevra consimilis – RDB:VU, primary strongholdDiptera – Chloropidae (Grass fly)This species occurs in the wetland without grazing guild. The species within this guild occur inwetlands, but open standing or running water is not essential, but obviously an environmentalelement in determining wetlands. This rare species is recorded from southern England. Thelarvae of this are inquilines of another species of grass fly (Lipara similis RDB: VU, BAP) galls onCommon Reed (Phragmites). Grazed wet grassland or heavily grazed fen would therefore, not besuitable for this species. However, low density extensive grazing or rotational biomass harvestingby reed cutting would be appropriate.Research by RSPB examining the effects of introducing highland cattle to wet fen in the mid-Yare,showed that grazing significantly reduced densities of three snail species, common Desmoulin’swhorl snail Vertigo moulinsiana, marsh whorl snail V. antivertigo and the land snail Euconulus alderi.However, because of the patchy nature of grazing, high densities of these species still persisted inless heavily grazed parts of the grazing unit. V. moulinsiana was particularly associated withvegetation dominated by greater pond sedge Carex riparia (RSPB 2002).Similarly at Thompson common Desmoulin’s whorl snail (Vertigo moulinsiana), whilst present ingrazed pingos, achieves higher populations in ungrazed situations (based on survey data from 2001;B Nichols pers. comm.) due to a requirement for a combination of low and tall vegetation structure.The same may also be true for other invertebrate groups including for aquatic Coleoptera, for whichpingos are an important resource (Martin Collier, Geoff Nobes, pers. comm.).178