Tower Mustard (Arabis glabra) - Species Action Plan

Ref 2/S20 Species Action Plan 20
Plan Author: Norfolk Wildlife Trust
Plan Co-ordinator: Heathland BAP Topic Group
Plan Leader: Forestry Commission
Final Draft February 2007

Action Plan Summary

Current Status

National Status

  • Although tower mustard has been recorded from a total of 133 10km squares, this declined to 28 squares between 1987 and 1999 (Preston et al, 2002). According to Plantlife, the current area occupied by the species is only 15% of its total historic area. The most significant cause of decline has been agricultural intensification on heathlands.
  • Extant sites occur within East Anglia (Breckland), the Midlands (Severn & Avon Vales) and southern England; west Norfolk is a particular stronghold. The species is widespread elsewhere in Europe, and is also found in western Asia.
  • In Great Britain, tower mustard is now classified as Endangered. It receives general protection under the Wildlife and Countryside Act 1981.

Norfolk Status

  • Almost confined to Breckland, tower mustard was found in 17 sites in Norfolk between 1988 and 1999. The majority of these sites are in forest rides, where the species can be abundant in some places. Forestry Commission records for the period 2000 to 2006, are given below:
Site 2000 2001 2002 2003 2004 2005 2006
Didlington Springs*     0 0 0 1 0
Stanton St/Harling Drove 79         155 118
Stanton St       1797 617 149 32
FR24             1
Barrow Hill         1    
4Score Plantation*     2 0 8    
Ickburgh*   400*          
Thetford-Danepak 17*            
Barnham Cross 157            
Harling Drove/Tunnel Track       26 10    
BromeHill Farm       0      

*Indicates ephemeral site.
  • Tower mustard has been able to colonise some areas of newly created habitat in Breckland, such as clear-felled conifer plantations. It is possible that the species may actually be increasing in numbers on some existing sites in Breckland where appropriate management is taking place. New and often ephemeral sites are frequently being discovered in forested areas due to translocation of tower mustard seed by forestry equipment.
  • Despite the implementation of appropriate management at Maine Road, the population of tower mustard at this site is in decline.

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Current factors causing loss or decline in Norfolk

  • Habitat destruction as a result of agricultural intensification and building development. The former would appear to be the main reason for the decline of this species in recent years. However, the colonisation of a few newly created sites in Breckland has helped to slow the overall decline of the species.
  • Habitat neglect, which results in a lack of open ground for regeneration and the development of coarse competing vegetation.
  • Overgrazing by rabbits, stock and deer. Although tower mustard is a Breckland species, there is evidence that it is susceptible to high levels of grazing.

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Current Action in Norfolk

  • The majority of sites are owned, managed and monitored by the British Trust for Ornithology, Plantlife or the Forestry Commission, and appropriate management is undertaken on all key (not ephemeral) sites where tower mustard occurs.
  • On sites that are not owned by the above mentioned organisations (e.g,. Barnhamcross Common, Seven Hills, Brettenham and Maine Road/Brandon Road sites), landowners are advised on appropriate land management for tower mustard.
  • The Brandon Road site has been designated as a Roadside Nature Reserve.
  • The Maine Road site is managed by the developer in conjunction with the Brecks Countryside Project, but has declined and further management is required.
  • Plantlife is currently carrying out an ecological study of tower mustard at Ickburgh. This includes experiments to investigate the response of tower mustard to various cultivation techniques. PhD student Jo Nightingale from the University of Sussex is studying the ecology and population dynamics of tower mustard from sites in Breckland.
  • The identification of new and often ephemeral sites continues; these are frequently being discovered in forested areas due to translocation of tower mustard seed by forestry equipment.

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Action Plan Objectives and Targets

National

  • Maintain the current (natural) range within twenty-six 10km squares.
  • Establish populations at three sites within the historic range by 2010.
  • Establish four meta-populations within the species current range by 2010.

Norfolk

  • As a minimum threshold, maintain the natural range of this species at or above 14 tetrads.
  • Establish populations at two new sites within the species' historic range by 2010.

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