When you look over a limestone pavement, at its bare rock and Hart's Tongue Ferns (Asplenium scolopendrium), there is a special feeling of being in a living time capsule. These ancient, dramatic landscapes are among the rarest habitats in Britain, but they are facing modern ecological threats. I feel incredibly lucky to be playing a part in their preservation through a new research project with the Limestone Pavement Partnership at Lancaster University. For me, this project is also a homecoming. I am Claire Holden and I was really excited to return to Lancaster Environment Centre after completing my PhD here in 2023.

Whilst I have a PhD in plant biology, the unique habitat of limestone pavements and the conditions it creates for plant life is a new area for me. Another member of the research group, Sian, has a geology background and has been really helpful in explaining the origins of the pavements.

Marine sediments 350 million years old were compressed into solid stone layers, and the loose rock was scraped away by glaciers in the last ice age to reveal flat sheets of limestone. Acidic rainwater dissolved and widened the vertical cracks to create the distinctive pattern of limestone pavements: flat blocks, "clints", separated by deep fissures "grykes". The contrasting microclimates of clints and grykes side-by-side is what makes these environments so interesting to me as a biologist. The tops of the clints are dry and exposed to the sun, allowing drought-tolerant plants, mosses, and lichens to survive. The deep grykes stay damp, shady, and hidden from grazing animals. This microclimate protects delicate ferns and woodland plants that cannot survive on the open rock.

An open pavement with no trees on farmland near a quarry in Yorkshire.

These woody species are the focus of my project. The absence of trees and scrubs is a major challenge for limestone pavements, with over half of pavements having less than 1% tree cover. There are several environmental pressures preventing tree establishment on the bare rock, such as grazing, thin soil accumulation, and wind exposure. One possible reason for the lack of tree colonisation is an absence of the correct mycorrhizal fungal communities. Mycorrhizal fungi form symbiotic relationships with most plant species where both the fungi and the plants benefit. Early colonist tree species, including birch and hazel, and later colonists, such as oak, need a specific type of mycorrhizal fungi called ectomycorrhizal fungi. To understand why trees may be struggling to return, my research will investigate whether ectomycorrhizal fungi are present in limestone pavements, contrasting pavements with no tree and shrub cover with those where trees and shrubs are found. This project will be conducted in collaboration with Dr Fay Voller from Edge Hill University, who specialises in microbial communities in habitats of conservation concern and habitat restoration projects. Fay and Carly went with me on my first fieldwork day in Hampsfell where we were blessed with some gorgeous sunshine, a perfect return to scientific fieldwork.

Professor Carly Stevens (Lancaster University) and Dr Fay Voller (Edge Hill University) sampling on Hampsfell near Grange over Sands. This was my first day out sampling and meeting our collaborator Fay.

My work requires collecting soil samples from various sites across the region. Many of the limestone pavements in the area are designated as Sites of Special Scientific Interest (SSSIs). SSSIs legally protect conversation areas to support rare and endangered plants, animals, ancient woodlands, and unique rock formations like limestone pavements. Conducting research on SSSIs means balancing science with conservation laws and taking into consideration the residents of the land. Speaking with landowners to gain permission has been really interesting for me and I have learnt a lot about the diverse uses of the UK's limestone pavements. Pavements may be neighbours to limestone quarries, used for livestock farming, in conservation areas, or sited at heavily trafficked public spaces, including famous walking trails like the Yorkshire Three Peaks (Ingleborough and Whernside).

The extra-long, specially welded soil auger, being used up at Hutton Roof

Limestone pavements come with their own practical considerations for fieldwork. The surface of limestone gets particularly slippery when wet, and the deep grykes present a challenge to reach the soil at the bottom, requiring an extended auger which was custom-made especially to provide extra reach. I have really enjoyed learning about this new habitat. It has also been wonderful to meet the rest of the team and interesting to learn about the other exciting work being conducted with the Limestone Pavement Partnership, for example, Carly and Ezra's grazing studies, Hannah's work on Lepidoptera (butterflies and moths), and Sian's soil studies.

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