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Mixed Results for UK Limestone Pavements After 50 Years
Changes observed over half a century in the UK’s iconic limestone pavements showcase a landscape of both decline and growth, highlighting the complexity of this unique environment.
Familiar to tourists in the Yorkshire Dales and depicted in popular culture, such as the “Harry Potter and the Deathly Hallows” film, these limestone landscapes are experiencing a shift in their ecological balance. While some areas have noted a decrease in specialized plant species, other regions have reported an increase in more commonly found species.
Overall, the assessment presents a diverse picture across various limestone pavement areas in the UK, with certain locations showing improved biodiversity. This national study is the first extensive survey of its kind in fifty years, led by Carly Stevens, a Professor of Plant Ecology at Lancaster University. The findings highlight significant ecological changes since the initial surveys of the 1970s.
These limestone landscapes are critical habitats, primarily located in northern English regions such as Yorkshire, Lancashire, Cumbria, as well as parts of North Wales and Scotland. The unique formations of these pavements create microhabitats known as grikes, where distinct flora like ferns and other herbaceous plants thrive, often hidden from view until directly observed from above.
Legal protections were introduced in the early 1980s to safeguard these pavements from quarrying, subsequently leading to the establishment of various nature reserves. Despite this status, scientific inquiries into these ecologically rich areas have remained scarce.
In an effort to fill this knowledge gap, Professor Stevens conducted a survey mirroring the methodology of Stephen Ward and David Evans from the 1970s. Over five years, from 2017 to 2022, her research encompassed 3,157 hectares of limestone pavement, revealing a total of 313 plant species — an increase of 29 compared to the original study.
While some pavements reported growing numbers of plant species, certain negative trends were also evident. Notably, less desirable species such as thistles and nettles have proliferated, overshadowing the decline of specialized plants like primrose and lily of the valley across various locations. Nonetheless, these declines were not consistent, as certain areas showed an increase in some previously declining species, presenting a complex conservation narrative.
“The transformation in both the quantity and diversity of plants in these remarkable habitats is striking,” stated Professor Stevens. “Given their ecological value, it is crucial to understand the forces driving these changes to ensure their conservation for the future.”
A prevailing influence on some of the limestone pavements is tree cover. Utilizing aerial photography to compare historical images, Professor Stevens found a significant increase in shaded areas due to tree growth, with some pavements experiencing greater than 50% increases in tree cover. Conversely, an increase in areas devoid of trees illustrated a varied vegetation landscape influenced by surrounding tree density.
Pavements subjected to greater tree cover often showed declines in plant diversity, likely attributable to reduced light availability for the smaller flora growing among the grikes. Notably, regions in Lancashire and Cumbria faced greater impacts from increased tree cover.
On the other hand, sites maintaining low to moderate tree cover had a higher tendency to see an increase in species richness, even if this did not always include desirable rare species. Professor Stevens also noted that many open pavements had faced challenges from animal grazing, with shifts in grazing pressures observed over the decades.
“While grazing levels have dropped in several areas due to changes in agricultural policy, some locations continue to experience overgrazing,” she explained. “Strategically managed grazing can support biodiversity in limestone habitats, but it must be balanced, as both over- and under-grazing can lead to diminished plant diversity.”
The results from this comprehensive survey not only shed light on the current state of limestone pavements but also signal the need for informed management strategies moving forward. “Presently, the optimal management practices for limestone pavements remain unclear,” added Professor Stevens. “This survey serves as a critical foundation for understanding their vegetation dynamics, but additional research is needed to identify threats and explore restoration opportunities for these precious habitats.”
The study is detailed in the paper, “Large changes in vegetation composition seen over the last 50 years in British limestone pavements.”
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