Summary for Haplodrassus umbratilis (Araneae)
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About this speciesDistribution
The species has been recorded from five sites in east Dorset and from Vales Moor on the western edge of the New Forest, South Hampshire, all since 1969. It probably occurs in several sites on the eastern side of the Avon Valley on the western fringes of the New Forest. In 1990 the British range of H. umbratilis was found to include Hadleigh Downs, South Essex (Harvey 1990). It is widespread in western and central Europe, but has not been recorded from Ireland.
Habitat and ecology
In Dorset and Hampshire H. umbratilis has been found on dry heathland in the building and mature phases. In Essex it occurred on a small area of steep south-facing landslip with grassland and scrub. Adult males have been found in May and June, females from May to August.
The spider has not been recorded from any location since 1990, an apparent decline of 100% in area of occupancy. Although its current status is unknown at any recorded sites, the spider was known to be abundant at Vales Moor and Cranborne Common, and it probably survives in at least five locations in east Dorset and the western edge of the New Forest.
Uncontrolled heathland fires and the loss of heathland to building development and agriculture. Previously abundant at Horton Common, but much of this site (100 ha) has now been ploughed up and is used for agriculture. The surviving twenty hectares of heath at Horton Common now have the protection of SSSI status. Knighton Heath is now a golf course with only a few banks of heath left, and even the golf course is under threat of building development. Much of Cranborne Common has been planted with conifers, only strips of heathland remaining. The remaining heath is now an SSSI and in part a Dorset Trust reserve. Heath at Stephens Castle lies within Verwood Heaths SSSI. It would seem to be probably fairly widespread on heathland either side of the Avon valley, but much of the heathland in that area is fragmented and subject to development of one sort or another. If the density of scrub at Hadleigh Downs increases, it may overrun the grassland required by this spider, and plans for this area to be host to the Olympic mountain biking event in 2012 and remain open to the public after the Games, threaten the habitat of this spider and a whole assemblage of rare and scarce species.
Management and conservation
Management to accommodate this spider requires patches of the heath to be regularly returned to the early stages of heather development on a long rotation, preferably well over a decade. This should ensure the permanent presence of the building and mature stages. It could be achieved by small-scale burning, or, where nearby pine plantations preclude this, heavy grazing for a short period or manual stripping of the vegetation could be attempted. At Hadleigh Downs, sufficient grazing is required to maintain patches of short sward and to prevent scrub encroachment. Some scrub clearance may also be necessary.
Text based on Dawson, I.K., Harvey, P.R., Merrett, P. & Russell-Smith, A.R. (in prep.). References
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