Genetic Scorecard Indicator - Yorkshire Fog

No evidence of declines (Braithwaite et al., 2006), but rather of human-mediated propagation for restoration.

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 (Hebert 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. Demographic (using the ratio Nc 5000 = Ne 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

Functional variation is well characterized, but not apparently under threat: Evidence of local adaptation in seed collected from chalk vs mesotrophic grasslands (Bischoff et al., 2006); used as a model system for genetics of metal tolerance (e.g. Meharg et al., 1993; Rahman and Khan, 2023). A recent transcriptomic study comparing plants from contrasting habitats (acid bog and limestone quarry) from Northern Ireland found ecotypic differences and distinct microbiome responses (Young et al., 2018).

Divergent lineages

No direct evidence of losses; widespread evidence of local adaptation to extreme conditions, e.g. metalliferous soil and climate (Macel et al., 2007), with studies showing different levels of tolerance to acidic soils rich in aluminium (Chen et al., 2013) performed in the UK.

Hybridisation/Introgression

Holcus mollis is the tetraploid counterpart to diploid H. lanatus (Rich & Jermy, 1998).  Some hybrids are known in the wild and can be produced by crossing (Beddows, 1961). Primary concern is hybridisation with non-local seed from restoration projects, but the species’ abundance limits the overall potential for negative impacts. 

Low turnover - constraints on adaptive opportunities

Large populations, reproduction mostly by outcrossed seed and ability to re-establish on disturbed sites (e.g. Lowday et al., 1992) suggests no limits to adaptive opportunities. Studies suggest a loss of biomass production due to drought (Beierkuhnlein et al., 2011).  

Scotland

• Risk: Negligible
• Mitigation: Negligible

Great Britain/UK

• Risk: Not required
• Mitigation: Not required

Overall Genetic Health status explanation

Though some potential risk from genetic swamping could be pinpointed in restoration projects using commercial seed, this species is able to colonize easily without seed additions (e.g. Lowday et al., 1992) and remains widespread and abundant. 

In situ genetic threat level

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

Widespread and large populations reduce impacts of any existing pressures. 

Confidence in in situ threat level

• Confidence score for Scotland: Medium
• Confidence score for UK: Medium

Assessment based on good demographic data supported by direct data on most aspects of species’ biology, cytotype distribution, and no major threats; however, no direct genetic data available.

Recent consideration of policy shifts towards using local seed in restoration should help mitigate any potential risks from genetic swamping (De Vitis et al., 2017; Abbandonato et al., 2018) .

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

Generation of whole genome sequencing data to given more direct insights into patterns of genetic diversity.