Genetic Scorecard Indicator - Heather

Habitat losses due to conversion and eutrophication over centuries have resulted in long, slow declines in heathland (Norton et al., 2009) and Calluna distribution (Braithwaite et al., 2006). Long-lived individuals and persistent seed banks (150 years) help ensure standing diversity. High levels of temporal and spatial gene flow minimize risks to genetic variation (Rendell & Ennos, 2002).

Population definitions:

Populations are defined based on management units. This species is widely and continuously distributed across UK in large numbers (Stroh et al., 2023; NBN, 2025). The four Great British Regions of Provenance (Herbert et al., 1999) were selected here to represent the major population groupings / management units (treating Northern Ireland as an additional region) as they broadly reflect the environmental variation across which the species is distributed and are likely to capture major patterns of genetic structure.

Ne500: The proportion of populations that have an effective population size of more than 500. 

• Proportion of populations with Ne > 500 in Scotland = 2/2
• Proportion of populations with Ne > 500 in UK = 5/5

PM: Proportion of populations that existed in 2000 that still exist in 2025.

• Proportion of populations maintained in Scotland = 2/2
• Proportion of populations maintained in UK = 5/5

Functional variation

Negligible imminent risk of loss of adaptive / functional variation, as despite demographic changes, Calluna remains abundant and widespread in Scotland and much of upland UK.

Divergent lineages

Negligible risk as no divergent lineages have been detected in genetic studies.

Hybridisation/Introgression

None known.

Low turnover - constraints on adaptive opportunities

Heavy grazing can lead to loss of stands and reduction of seedling establishment (Stevenson & Birks, 1995), but seed banks have similar levels of genetic diversity as above ground plants (Mahy et al., 1999b). Overall, negligible risk from limits on turnover.

Scotland

• Risk: Negligible
• Mitigation: Negligible

Great Britain/UK

• Risk: Not required
• Mitigation: Not required

Overall Genetic Health status explanation

Populations in Scotland and UK are large with little imminent risk of genetic diversity loss.

In situ genetic threat level

• In situ Risk for Scotland: Negligible
• In situ Risk for UK: Negligible

There has been significant population declines UK-wide, but the plant exists in extremely large populations with no evidence of unique variation in UK.

Confidence in in situ threat level

• Confidence score for Scotland: High
• Confidence score for UK: High

Based on good distribution data and by direct data on most aspects of species’ biology including population level variation.

Species largely protected by wider habitat management efforts.

Population

Demographic

N pops assessed/monitored in Scotland = 2/2
N pops assessed/monitored in UK = 5/5

Genetic

N pops assessed/monitored in Scotland = 0/2
N pops assessed/monitored in UK = 0/5

Genetic surveys utilising the Darwin Tree of Life reference genome and subsequent resequencing across populations would provide more directly quantified insights into patterns of genetic diversity.

NBN Atlas Website

APIS, 2019. Nitrogen deposition - dwarf shrub heath. 

Bobbink, R., Hicks, K., Galloway, J., Spranger, T., Alkemade, R., Ashmore, M., Bustamante, M., Cinderby, S., Davidson, E., Dentener, F. Emmett, B., Erisman, J-W., Fenn, M., Gilliam, F., Nordin, A., Pardo, L. & De Vires, W. 2010. Global assessment of nitrogen deposition effects on terrestrial plant diversity: a synthesis. Ecological Applications, 20(1), 30-59.

Braithwaite, M.E., Ellis, R.W. & Preston, C.D. 2006. Change in the British Flora 1987-2004. Botanical Society of the British Isles, London.

Gimingham, C. 1960. Calluna, a monotypic genus. British Ecological Society, 48, 455-483.

Herbert, R., Samuel, S., & Patterson, G. (1999). Using Local Stock for Planting Native Trees and Shrubs. Forestry Commission Practice Note. 

Mahy, G., Ennos, R.A. & Jacquemart, A-L. 1999a. Allozyme variation and genetic structure of Calluna vulgaris (heather) populations in Scotland: the effect of postglacial recolonization. Heredity, 82(6), 654.

Mahy, G., Vekemans, X. & Jacquemart, A.L. 1999b. Patterns of allozymic variation within Calluna vulgaris populations at seed bank and adult stages. Heredity, 82(4), 432.

Marrs, R.H., Phillips, J.D.P., Todd, P.A., Ghorbani, J. & Le Duc, M.G. 2004. Control of Molinia caerulea on upland moors. Journal of Applied Ecology, 41(2), 398-411.

Mitchell, R.J. (2023). Plant Health and the Natural Environment: Project Final Report. PHC2020/03. Scotland's Centre of Expertise for Plant Health (PHC). DOI: 10.5281/zenodo.8297811

Norton, L.R., Murphy, J., Reynolds, B., Marks, S. & Mackey, E.C. 2009. Countryside Survey: Scotland Results from 2007. NERC/Centre for Ecology & Hydrology, The Scottish Government, Scottish Natural Heritage, 83pp.

Rendell, S. & Ennos, R.A. 2002. Chloroplast DNA diversity in Calluna vulgaris (heather) populations in Europe. Molecular Ecology, 11(1), 69-78.

Stevenson, A.C. & Birks, H.J.B. 1995. Heaths and moorland: long-term ecological changes, and interactions with climate and people. In: D.B.A. Thompson, A.J. Hester & M.B. Usher, eds. Heaths and moorland: cultural landscapes. HMSO, Edinburgh. pp. 224-239.

Stroh, P.A., Walker, K.J., Humphrey, T.A., Pescott, O.L. and Burkmar, R.J., 2023. Plant atlas 2020: mapping changes in the distribution of the British and Irish Flora. Princeton University Press.