The secret world of plants that live on limestone pavements

Anyone who walks through the Yorkshire valleys in winter will probably be familiar with the dramatic scenery of limestone pavement. This distinctive and beautiful plant can be found in other parts of the UK, as well as mainland Europe and Canada. Not to mention, it’s also seen in Harry Potter and the Deathly Hallows, where Harry and Hermione set up camp on a rocky cliff.

Limestone pavement was formed during the Dinantian period more than 300 million years ago, when ice sheets scraped away the soil and exposed limestone rock. Over time, rain wore away the rock, creating the uneven pattern we see today.

Limestone pavements are made up of large rock slabs called clints, dotted with cracks called glykes that can be up to several meters deep. Inhabiting these glykes is a secret world of plants, including rare species such as the dainty white mountain aven, the poisonous baneberry, and the hard buckler fern, which only grows on limestone.

Why are these areas important?

These grike habitats are important for conservation because limestone pavements only cover an area of ​​around 28 square kilometers across the UK, the area of ​​a small town. In the 1970s, a landmark national survey of British limestone pavements led by two scientists, Stephen Ward and David Evans, led to increased protection for limestone pavements.

This was necessary because many pavements were being damaged by people removing rocks for construction and decoration. Individual sites were designated as protected areas or sites of special scientific interest. Then in 1981 the Wildlife and Countryside Act introduced the Limestone Paving Order, making it illegal to remove limestone.

I have spent five years working on a new national study to find out what has happened to pavements and the plants that surround them over the past half century. The study, published in Functional Ecology, revisited the same locations as the 1970s study, including northern England, Scotland and Wales. I found a very complicated picture.

In some areas, sheep and cattle grazing has ceased or been reduced. In the 1970s, farmers were paid by the then European Economic Community (EEC) for each animal they grazed, but now they receive money for managing their land for conservation purposes.

Although this reduction in grazing intensity is positive in most cases, it has resulted in shrubs and trees encroaching on the pavement in some areas. This can reduce the amount of light to other plants and has often been found to significantly reduce biodiversity. For example, some areas of the pavement where tree cover had increased significantly lost more than 20 plant species in the years between the two surveys.

On the positive side, reduced grazing intensity also means that some pavement tree species that are particularly sensitive to grazing, such as baneberry, appear to be increasing. But by the same token, not all increased species are desirable. There has been a significant increase in thistles, especially creeping thistles, which are not found on limestone pavements and can be disruptive to the ecosystem.

Just as the area of ​​sidewalks covered with trees and shrubs has increased, so too have areas with no trees at all. In these areas, the pavement is actually overgrazed. For example, sheep lower their heads as far below the ground as possible to reach the plants they want to eat.

This can also affect the ecosystem. Some species are being over-fed (although we do not collect data on which species), while high nutrient levels on footpaths from sheep dung can lead to over-competitive species such as nettles. The number of certain species is increasing.

More generally, it is surprising how little research has been done on limestone pavements and the plants that grow on them. This is despite its importance for conservation and many areas are now nature reserves.

It is important to have evidence to support decisions about how best to manage these natural habitats, so building a solid research base will be a future priority. My research will play a part in this, but there is much more to learn, including how these habitats will respond to climate change, to ensure that our wonderful limestone pavements remain special for future generations. There are still many things to do.

This article is republished from The Conversation under a Creative Commons license. Read the original article.