Genetic Scorecard Indicator - Flotow's Rock Dimple

Population declines have been severe in the UK, with modelled declines of over 30% to nearly 70% since 1980 (UK CEH) and increasing population fragmentation with losses across entire regions. Although recording is not at all complete, the magnitude of this modelled decline is supported by the loss of veteran elm trees in the south and the ongoing and increasing losses of ash trees.

Population definitions:

Populations are defined by ecological and biogeographic proxies. The four GB 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 = 0/2
• Proportion of populations with Ne > 500 in UK = 0/5

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

• Proportion of populations maintained in Scotland = 1/2
• Proportion of populations maintained in UK = 3/5

Functional variation

Concomitant with significant losses of habitat and known sites, it is expected that functional variation will also be lost, but there is no direct evidence of this.

Divergent lineages

Along with significant losses of habitat and known sites, it is expected that divergent lineages may also be lost, particularly in the south of the UK, where most elm trees have been lost, but there is no direct evidence of this.

Hybridisation/Introgression

There is no evidence of hybridisation or introgression in this species and no studies of these potential effects within the genus.

Low turnover - constraints on adaptive opportunities

Populations are very small due to the lack of suitable habitats (trees), and microhabitats (rain or wound tracks) may be further limiting. Therefore, propagule pressure is likely to be very low, probably limiting dispersal and establishment in this species. The species has small spores compared with congeners, which may also limit its ability to establish.

Scotland

• Risk: Serious
• Mitigation: Not effective

Great Britain/UK

• Risk: Serious
• Mitigation: Not effective

Overall Genetic Health status explanation

The species is at severe genetic risk due to small, declining and fragmented populations.

In situ genetic threat level

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

The species is apparently rare across its distribution, with small populations, marked declines and significant fragmentation.

Confidence in in situ threat level

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

Although this is a small and easily overlooked species, there is a high level of confidence in the threat assessment because of consistency in risk factors across its range: the species appears to be rare throughout its range, and population declines are well-supported by the losses of elm and ash trees throughout, with high levels of fragmentation due to historic losses.

None. 

Some survey work is ongoing, and efforts to increase pathogen-resistant ash and elm trees are underway; however, these are unlikely to produce the old tree habitats required by these species at the same rate as older trees are being lost. 

Population

Demographic

N pops assessed/monitored in Scotland = 1/3
N pops assessed/monitored in UK = 3/5

Genetic

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

UK CEH, 2024. Modeled data for UK Lichen Red Listing.

Image © Jaques Haine