Invertebrate survey at Gunpowder Park, the former Royal Ordnance Site in the Lee Valley
The Essex threat statuses used for aculeate Hymenoptera, spiders, harvestmen, woodlice and
hoverflies are based on the definitions used for ants (Harvey 1998) and harvestmen (Harvey 1999).
In general Essex Red Data criteria are based on the following:
on the national Red Data List (where one exists), irrespective of the frequency in Essex;
Nationally Scarce/Notable species (where there is an available definition and list),
again irrespective of the frequency in Essex;
for species which are not in either of the above categories, those which are rare and/or
threatened in Essex. Depending on the degree of regional knowledge this is related to
species recorded in few modern sites; species with restricted distribution occurring in
habitats under a high degree of threat nationally and/or within the county; more
widespread species which have undergone a substantial decline in number or
distribution since 19XX. The values of X will differ for different taxonomic groups.
Watsonian Essex Threat Categories
Watsonian Essex threat categories are based on the following:
Essex Endangered species which are known as a single extant population within a single
post 1980 one km square or only from a threatened or vulnerable sites
in the county.
species believed extinct in the county but which if rediscovered would
need protection.
Essex Vulnerable species known from only two extant populations within the county.
Essex Rare species which are restricted to habitats or sites known to
be under threat in the county e.g. from agricultural improvement,
development or inappropriate management.
species which only occur at sites within the county known to be
vulnerable.
species which have shown a continuous decline over the last twenty
years and arc now known to exist in less than 1% of the covered post
1980 one km squares in the county,
Essex Threatened scarce species with an Essex rarity status of Rare or Scarce and with a
Frequency Ratio of less than 1.5 and Tetrad percentage of less than
1.0 indicating widely isolated populations within the county.
Essex Scarce species which arc restricted to habitats or sites known to
be under threat in the county e.g. from agricultural improvement,
development or inappropriate management.
Essex Naturalist (New Series) 21 (2004)
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