Securing Biodiversity in Breckland - European Commission

The Feasibility and Usefulness of the Ecological Assemblage ApproachIt proved possible to attribute 84% of species to an assemblage, based on an objective analysis ofindividual ecological requirements collated from documentary and expert sources. Where there wasuncertainty regarding responses to important ecological processes such as grazing or disturbance,then species were retained within a general guild for their key habitat type.65 guilds were identified of which 25 were dry terrestrial guilds and 31 wet habitat guilds (Figures 20and 22). The remaining nine guilds comprised species requiring damp conditions and those thatneeded specific ecological processes or structures, such as dung, but could occur in any habitat orecotone. The mean number of species within all the guilds was 29 species.For wetland species, 31 assemblages were identified that ranged in size from 1 to 94 priority species(mean 19.3 species per guild) (Figure 23). Of these, 10 guilds contained fewer than five priorityspecies. In many cases this reflects our difficulties in collating suitably detailed knowledge orecological understanding for large numbers of the wetland species. For example, in the open wetlandguilds (open wetland associated species with no aquatic life-stage) only two species were attributedto require disturbance or disturbance in combination with grazing, while 94 species were placed in acategory of uncertain response to disturbance and grazing. Similarly for standing and running waterassemblages, a few individual species were attributed to ungrazed, or disturbed and grazedconditions, while for the large majority we were uncertain of their response to disturbance andgrazing. Other small assemblages may reflect highly specialist groups that are poorly represented inBreckland, for example species of deadwood in damp woodland and species of veteran trees in wetwoodland.For dry terrestrial species, including open woodland and woodland associates, fewer but largerassemblages were identified compared to the wetland guilds. Twenty five assemblages, ranging insize from 2 to 156 priority species (mean 46.8 species per assemblage) (Figure 21). Only three ofguilds comprised fewer than five priority species and all were associated with woody vegetation.These were guilds of species requiring: Veteran trees in open woodland (a specialist group poorly represented in Breckland). Open, grazed habitats without a requirement for disturbance, but that also have arequirement for scrub – a guild better regarded as a sub-group of a larger assemblage. Open, ungrazed woodland (compared to a much larger assemblage of open woodland speciesfor which the grazing and disturbance requirements were unknown).The largest guilds were; woodland (156 species), open with disturbance no/light grazing (136 species)and open with disturbance and grazing (117 species). The guilds with the highest numbers of RedData Book species were; open with disturbance no/light grazing (67 species), wetland withrequirements uncertain (44 species) and woodland (43 species).Breckland specialists occurred in almost half of all the guilds (34). The largest number of specialistswere in the open with disturbance and grazing guild (30 specialist species) and the open withdisturbance no/light grazing guild (also 30 specialists), followed by the open with disturbance butuncertain grazing (17 specialists). The disturbance-and-grazing guild contains 136 Brecklandconservation priority species and 23% (30 species) of these are Breckland specialists.115