Methodology
1. Habitat networks for red squirrels were identified using Geographic Information System (GIS).
Habitat networks are connected woodland areas which red squirrels can readily move between.
Networks were required to have at least 1 patch of conifer habitat greater than 200ha in size. This is the minimum patch size believed to be required to support a self-sustaining, viable population of red squirrels (Pepper & Patterson, 1998) and was included to act as a source for smaller patches of woodland within the network.
The networks were also required to contain at least 2000ha of conifer forest in total, as areas above this size are considered to be “ideal to conserve a population of red squirrels with a high chance of success” (Pepper & Patterson, 1998).
2. Networks with no records of red squirrels within the boundaries within the last 10 years were excluded.
3. Networks with more than 5 grey squirrel records within the last 10 years were excluded.
4. Sites were scored for the following criteria using nationally-available datasets:
- Functional distance (as the squirrel moves) to the nearest grey squirrel
- Proximity to grey squirrels with squirrelpox
- Percentage area overlap with ancient, semi-natural broadleaf woodland
- Area of network defined as conifer woodland.
5. Sites were scored for the following criteria by discussing maps of the sites with Forestry Commission Scotland and Scottish Natural Heritage field staff:
- Proportion of large seeded broadleaves
- Conflict with existing or planned built development
- Conflict with other conservation objectives
- Silvicultural factors constraining stronghold management
- Likely defendability against grey squirrel incursion
- Red squirrel presence
6. The objective criteria were scored from 0 to 4 or 5 while information gathered through staff consultation was scored from 0-2 or 3.
7. Scores were totalled, with the best 18 sites being presented as candidate stronghold sites.
8. The list of candidate stronghold sites was modified following discussions with land managers.
- For more information, see Methodology PDF (265k).
References
Bryce, Cartmel and Quine (2005). Habitat use by red and grey squirrels: Implications for habitat management.
Gurnell, J; Rushton, S; Lurz, P; Sainsbury, A; Nettleton, P; Shirley, M; Bruemmer, C; Geddes, N. (2006). Squirrel poxvirus: Landscape scale strategies for managing disease threat. Biological Conservation 131.
Lurz, P; Garson, P; Rushton, S. (1995). The ecology of squirrels in spruce dominated plantations: implications for forest management. Forest Ecology and Management 79.
Scottish Red Squirrel Action Plan 2006-2011 (PDF). Scottish Natural Heritage/Forestry Commission Scotland/Scottish Executive (2006
Pepper, H and Patterson, G (1998) Red Squirrel Conservation. Forestry Commision Practice Note 5.
Poulsom, L; Griffiths, M; Broome, A; and Mayle, B. (2005). Identification of priority woodlands for red squirrel conservation in North and Central Scotland: a preliminary analysis. Scottish Natural Heritage Commissioned Report No. 89 (ROAME No. F02AC334).
Ray (2008). Impacts of climate change on forestry in Scotland - a preliminary synopsis of spatial modelling research. Forestry Commission Research Note 101.
Acknowledgements
Sian Williams’ work to identify the stronghold sites using GIS forms the basis of this work, and her input is gratefully acknowledged.
Expert help was provided at all stages by Forest Research, in particular the Landscape Ecology team; and by the FCS CGIS team. SNH and FCS staff have provided valuable comment and expertise; the input of field staff is particularly appreciated.
Other sources of assistance include members of the Scottish Squirrel Group, local red squirrel conservation officers and staff from the University of Newcastle.
