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Most commons and heathlands have either become secondary woodland through neglect or have
long since been ploughed. Very few heathland remnants remain but there are plans to restore
heathland in the county through the Biodiversity Action Plans and some significant areas of old
grazing marshes survive.
Conservation status of species in Essex
The audit of our biological resources and selection of species most in need of conservation is
fundamental to the biodiversity planning process and is urgently needed for Essex and other
parts of south-eastern England where modern farming techniques and development pressures
have decimated so much of our wildlife habitat. The identification on a regional basis of the
most vulnerable species is extremely important so that their conservation can be incorporated
into the planning process and management of land.
Regional status categories used in this paper
There arc many problems associated with assigning rarity categories to species and in the
comparison of species distribution from county to county, not least in the difficulty of ensuring
adequate recording coverage and scientifically comparable data. In order to make any kind of
sense nationally, and to allow comparative assessments of sites in nature conservation and
planning terms it seems essential that regional Red Data Book categories are comparable.
Unfortunately at present there is little evidence of a consensus on how to define regional status
categories and comparison between counties is difficult.
Plant (1993) provides a comprehensive example of the definition of regional distribution and
status categories for the LNHS London Arca. Mahon & Pearson (1993) define Dorset Scarce
Species as occurring in three or fewer sites in the county and Archer (1998) defines Yorkshire
Rare species as species that have been found in six or fewer 1km squares (solitary wasps and
bees) or four or fewer 10km squares since 1970 (social wasps), five or fewer 10km squares
since 1961 (ants) and seven or fewer 10km squares since 1980 (social bees).
Some of the most important factors to be considered include not only the rarity and frequency of
a species but also threats to populations, sites and habitats and any documented declines or
increases in distribution or frequency either nationally or regionally. Species associated with
habitats under threat regionally, species restricted to habitats or sites that have become
fragmented and isolated, species associated with habitats under threat nationally but which are
well represented in the county and species associated with specific habitats where the county
contains a large percentage of the national habitat will all constitute taxa deserving regional
conservation status.
In this paper regional categories are provided for species both on the basis of their distribution in
Essex and on perceived threats to their county populations or habitats. Each species is given
two regional status categories, a Watsonian Essex Distribution category and a Watsonian Essex
Threat Category. These follow the methodology used in the author's paper on the Ants of Essex
(Harvey 1998) but with several modifications to clarify status definitions, the introduction of an
Essex Ubiquitous rarity category to follow Morris (1998) and an Essex Unknown category for
species where there is insufficient data available to determine a reliable threat status but which
Essex Naturalist (New Series) 16 (1999)