Pale Bristle Moss

Durham Priority Species
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Pale Bristle Moss Action Plan

Priority Species: Pale Bristle Moss

Priorities
1. Protect and maintain the existing populations of pale bristle-moss on all known sites.
2. Establish and maintain a comprehensive understanding of the distribution, status and ecological requirements of pale bristle-moss through research, survey and monitoring

Targets
Vision Statement: To ensure that all known sites are protected and appropriately managed. To expand the population through habitat management and/or creation

Target Type Unit Value
1. To maintain the range of pale bristle moss in the Durham BAP area. maintain occupied km squares 5

Orthotrichum pallens is a rather small and inconspicuous species of moss that may well be under-recorded.  However the species displays a number of characteristics helpful for identification purposes, including the pale shiny appearance of the calyptra in early summer that gives the moss its common name.  A full list of species characters is given in a Plantlife/Natural England report [Hodgetts 2003].

Pale bristle-moss has a scattered distribution in northern Europe. It is extremely rare in the UK and as yet little is known of its ecology. It was described in 1827 and first recorded in Britain in 1842 at Clifton Ings near York. Until recently the last accepted record was in 1934 from Bolton Abbey Woods.

In 1999/2000, however, several new colonies were found along a short length of Weardale in County Durham. Of the 19 confirmed UK records since 1960, 16 are from Weardale.

Pale bristle-moss occurs on thin, often dead or dying, twigs and branches of many species of tree.  It appears to prefer trees and shrubs with fissured and deeply textured bark such as elder, willow, ash, elm and sycamore.  It was also found on alder (not normally a good substrate for mosses and liverworts) and holly.

Pale bristle-moss appears to be a colonist species, producing many small spores to facilitate dispersal and colonisation. The colonies themselves are probably relatively short-lived, and displaced easily by other more competitive species.

Local status

All recent and confirmed records for pale bristle-moss in County Durham are from Weardale between Crook Beck and Witton Park in the east and Harehope Gill in the west. They include sites at, or near, Crook Beck, Green Bank, Harehope Gill, Harperley Hall, Holebeck House, Witton Park and Wolsingham. The best of these sites, in terms of the quality and extent of habitat, is at Wolsingham.

Although it is likely that pale bristle-moss occurs undetected at other nearby sites it does seem to be restricted in its occurrence in Weardale, not being found on apparently suitable trees on downstream sites. The 2003 survey, however, was not carried out at an ideal time of year or in the best conditions, making identification difficult.

Pale bristle-moss has recently been found (2003) at most of the local sites where it was previously recorded in 1999-2000.

Threats

  • Lack of knowledge of its ecology
  • Probable under-recording of colonies
  • Loss of host trees in suitable scrub and woodland habitat
  • Removal of suitable deadwood habitat after clearance/thinning operations
  • Drift of agricultural chemicals
  • Acidification of bark from atmospheric CO2, leading to loss of suitable growing conditions. It has been suggested that the closure of the Eastgate cement factory may result in the lowering of the pH of tree bark on sites downwind, however the potential impact of this on pale bristle-moss is not understood.
  • Dust/particulate pollution altering the chemistry of the tree bark substrate.
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