Pyrenula hibernica is an epiphytic lichen with a very limited number of known subpopulations and a high degree of fragmentation. The main habitats of this species are Atlantic hazelwoods in the UK and Ireland and native laurel forests in Macaronesia, where it has been found on Ilex perado, Laurus azorica and Acer sp. On the British Isles, it is mostly found on the smooth-barked shoots of old-growth hazel shrubs in moist ravines, which are located along the Atlantic coast of the UK and Ireland. These woodlands are temperate rainforests and are dependent on the hyperoceanic climate present there. The abundance and quality of temperate rainforests is limited, since many stands are degraded due to overgrazing and other threats. There are only four records available from Macaronesia, however it is suspected that a significant part of this species’ population is in fact present on these islands (Aptroot, personal communication). The native laurel forest is mostly extirpated and the land converted to pastures. The remaining forested areas (~2%) are very fragmented and only some are in protected areas. Thus, this lichen is threatened by a small AOO, suspected small population size, small subpopulation size, severe fragmentation and habitat loss and decline.

There is debate about this species’ delimitation to Parmentaria chilensis (Etayo & Aptroot, 2003; Woods & Coppins, 2012).

Pyrenula hibernica is an epiphytic lichen with a very limited number of known subpopulations and a high degree of fragmentation. The main habitats of this species are Atlantic hazelwoods in the UK and Ireland and native laurel forests in Macaronesia, where it has been found on Ilex perado, Laurus azorica and Acer sp. On the British Isles, it is mostly found on the smooth-barked shoots of old-growth hazel shrubs in moist ravines, which are located along the Atlantic coast of the UK and Ireland. These woodlands are temperate rainforests and are dependent on the hyperoceanic climate present there. The abundance and quality of temperate rainforests is limited, since many stands are degraded due to overgrazing and other threats. There are only four records available from Macaronesia, however it is suspected that a significant part of this species’ population is in fact present on these islands (Aptroot, personal communication). The native laurel forest is mostly extirpated and the land converted to pastures. The remaining forested areas (~2%) are very fragmented and only some are in protected areas. Thus, this lichen is threatened by a small AOO, suspected small population size, small subpopulation size, severe fragmentation and habitat loss and decline.

Pyrenula hibernica is a species occurring in temperate hazel rainforests in the UK and Ireland and in native laurel forests in Macaronesia. It has a known EOO of around 2,300,000 km2 and a known AOO of 80 km2. A record from Madagascar (Aptroot, 2016) is not considered in this assessment, since there is uncertainty about it belonging to the species discussed here and about the extent of possible genetic exchange. We suspect that the true AOO is likely to be <5ha, and patches more than 20 ha are very rare (DellaSala, 2011).

On the Canaries (Tenerife) and Azores (Terceira), the habitat of Pyrenula hibernica is likely the native temperate laurel forest, since it was found on Ilex perado and Laurus azorica, which occur in those forests and since it needs long, undisturbed periods to establish. This habitat is threatened by land use change (mostly conversion to grazing land for cattle) and by invasive species. The laurel forest on the Canary Islands has been almost completely extirpated and the largest fragment left is in Garajonay National Park on la Gomera (39 km2). On the Azores, the native laurel forest is only left on the peaks of the islands’ mountains and is very fragmented. Protected areas exist, but are often not effective due to small size or lack of legal protection (Fernández-Palacios et al., 2011). It is estimated that only 2% of the native laurel forest is left on the Azores (WWF, 2026).
This lichen is likely severeley fragmented, since most occurrences are found in ravines and colonised forest patches are often small and with a limited number of functional individuals. However, given the limited data availability and the need for further surveys, severe fragmentation cannot be diagnosed.

There are fewer than 100 records of this species in total, across fewer than 20 subpopulations. At key sites, there can be up to 50 functional individuals in a subpopulation, but some subpopulations are smaller than this. All known subpopulations have fewer than 250 occupied hazels. There will very likely be undiscovered subpopulations and the uncertainty about the true population size is quite high, especially considering the limited data availability from the Azores and the Canaries. However, we suspect that the true population size is smaller than 2,500 functional individuals, since suitable habitat is very limited throughout the range. Since continuing habitat decline can be estimated (see below) we suspect that the population size of this species is declining too. Considering this, together with the observed and estimated population and subpopulation size, Pyrenula hibernica triggers the threshold for EN under criterion C2a(i).

This species is an epiphytic lichen associated exclusively with old-growth temperate rainforests. The majority of records are from Atlantic hazelwoods on the British Isles, and the specimens from Macaronesia were found in native laurel forest. Both habitats are characterized by hyperoceanic climate, experiencing high rainfall and mild temperatures. Some hazel stands are estimated to be up to 10,000 years old, having established themselves after the last ice age and probably having persisted since then (Birks, 1989). If mostly undisturbed and unmanaged, hazel can from pure stands with a closed canopy (Coppins & Coppins, 2003). Hazel will continuously form young shoots for rejuvenation, even if uncoppiced. Pyrenula hibernica is restricted to growing on the bark of these hazel regeneration shoots in old-growth, unmanaged stands. It is part of the Graphidion, a community of crustose lichens growing on smooth bark of the young hazel shoots. As described (Geographia Range), the atlantic hazelwoods in the Britain and Ireland are highly fragmented. They face a continuing decline due to unsuitable grazing regimes, invasive species and other threats (see Threats).

The native laurel forests of the Azores and Canaries are likely the native forest type for the submontane regions of the islands, as modelled for the Azores (Elias et al., 2016). Pyrenula hibernica is known from Ilex perado, Laurus azorica and Acer sp.. Once abundant, these forests are now reduced to small patches (see Geographic range) and a continuing decline of this habitat is suspected.

In the Atlantic hazelwoods, Pyrenula hibernica and other species from the Graphidion are dependent on the continuous cover of old-growth stands and continuity and regular supply of young, smooth bark. Overgrazing is a major threat to the persistence of temperate rainforests, with 41% of it showing the impact of high or very high grazing pressure (Alliance for Scotland’s Rainforest, 2019). High or very high grazing pressure restricts or impairs the regeneration of these forests. Under these conditions, the hazels cannot rejuvenate, thus not forming young shoots and become tree-shaped. The bark becomes exposed and young bark supply, which is needed for the establishment of the Graphidion, is low, and old stems collapse and die (Coppins & Coppins, 2012). Appropriate management of the remaining old-growth, intact woodlands is key for the survival of P. hibernica. This involves restricting deer and cattle grazing. However,  Interestingly, undergrazing also poses a threat to this species: When left completely undisturbed, understory woody species can invade the stands. The Welsh sites show signs of undergrazing.

Since hazel is the primary habitat of P. hibernica on the British Isles, management practices that harm its abundance and the quality of habitat it provides for crustose lichens pose a threat to P. hibernica (Coppins & Coppins, 2003, 2012). Another threat to this species is excessive coppicing, which can have negative effects on these ancient woodland stands. Outside Scotland, coppicing is used to rejuvenate hazel and encourages it to from new shoots, but this practice was not used across traditionally managed stands on the west coast. Hazel plants will continue to form new shoots throughout their lifetime, and allowing old stems to persist alongside young ones promotes short-distance colonization within stools. Coppicing therefore breaks the ecological continuity which promotes the epiphyte diversity in these stands. In addition, hazels are pioneer plants, which do not thrive under closed canopy cover. Coppicing an entire stand will limit competitiveness against other woody species in the stand and can lead to hazel becoming an understory shrub. This will risk it being shaded out and will limit its ability to reproduce, leading to a decline of hazel populations.

Rhododendron ponticum is invasive in rainforests on the British Isles, colonising the woodland and outcompeting native tree species (Alliance for Scotland’s Rainforest, 2019; Woodland Trust Scotland). Threatening the integrity of the Atlantic temperate rainforest ecosystems as a whole, this invasive species also poses a threat to the habitat of P. hibernica.

Climate change will likely have an impact on the persistence of P. hibernica, especially when the high fragmentation of habitat is taken into account. The climatic suitability of ancient forest habitats in Scotland was estimated to decrease by 42% for ancient forest indicator species under projected climate change scenarios (Ellis, 2015). To persist, species highly specialised for this habitat and climate must partly shift their distribution. However, ancient woodland specialist species are thought to be limited in their ability to disperse or establish (Sillett et al., 2000), and thus to have trouble migrating to track changing climatic conditions. The dispersal problem is exacerbated by the fragmentation of Scotlands ancient woodlands, making range shifts more difficult with larger gaps of unsuitable habitat that dispersal kernels have to traverse.
Little is known about the size or state of the Macaronesian populations of P. hibernica. Their habitat however, the native laurel forest, has faced an immense decline during the last decades due to conversion to pasture and is estimated to cover only 2% of its former range today on the Azores (Azores Temperate Mixed Forests, 2022; Azores Temperate Mixed Forests | Ecoregions | WWF, 2026) and a few patches left on the Canaries, including Garajonay National Park on la Gomera. Protected areas exist, but are often not effective due to small size or lack of legal protection (Fernández-Palacios et al., 2011).

On the British Isles, around 80% of known records are in protected areas, mostly Sites of Special Scientific Interest. However, this does not automatically imply that threats are absent. For example, it is known that even amongst protected parts of the Scottish Atlantic rainforest, around 50% are in undesirable condition (Alliance for Scotland’s Rainforest, 2019). Some of the threats mentioned above can be met with appropriate management. A restriction of deer and cattle grazing in hazelwood stands allows for young shoots to persist, which are the habitat of Pyrenula hibernica. Care must be taken however to avoid undergrazing; grazing pressure has to be balanced to an adequate amount. In addition to that, coppicing in old growth stands should be avoided; instead, selective cropping is advised (Coppins & Coppins, 2003). This allows the stands and its epiphytes to persist and the Graphidion community can develop in the shelter of a closed hazel canopy. Efforts should be made to control the invasive Rhododendron ponticum, not only to protect epiphyte flora, but the temperate Atlantic rainforests as entire ecosystems. Similarly, in Macaronesia, protection of this species can be achieved by protection of its habitat. Further loss of the laurel forests should be avoided and existing patches protected.

Given the limited data availability, survey work is recommended for this species, especially on the Azores and the Canaries. Gaining better knowledge of the distribution and habitat requirements are crucial to inform conservation measures. We recommend the record from Madagascar to be discussed in the scientific community and if needed, studies carried regarding the degree of interbreeding between the known populations.