Limestone pavement took ten thousand years and takes minutes to damage

The points below about limestone pavement are ordered by how much difference they make, not by how often they get repeated.

How it forms

Glaciers stripped the soil from horizontal limestone beds, exposing bare rock. Rainwater, slightly acidic, then dissolved the rock along existing joints over thousands of years.

The result is a pattern of blocks and deep fissures — clints and grikes — that is essentially unrepeatable on human timescales. Most of that dissolution happened beneath a cover of soil and vegetation rather than in open air, which is why the fissures are so regularly spaced and why the bare rock we see today is a comparatively recent and largely human-made condition.

The fissures are the habitat

Grikes are humid, sheltered and shaded, producing conditions closer to woodland than to open hillside. Ferns, hart's-tongue, dog's mercury and other woodland species grow in them, sometimes metres from exposed limestone grassland. That juxtaposition of two plant communities within a metre is what makes the habitat unusual.

A grike buffers both drought and frost, holding humidity through a dry spell and staying above freezing when the surface does not, which is how it supports plants that have no business growing on an exposed hillside at that altitude.

Removal was industrial

Large quantities were lifted and sold as weathered garden rockery through the twentieth century. A substantial proportion of the total resource in some countries was removed before protection arrived. The rock is now protected in many places, and enforcement remains an issue.

Locally, demand has not gone away, and the response has been reclaimed stone and manufactured substitutes, though distinguishing weathered pavement from a reclaimed garden wall is hard enough that provenance paperwork is the only real check a buyer has.

Walking on it

The surface is slippery when wet and the grikes are deep enough to break a leg. Beyond the personal risk, footfall damages the fragile plant communities in the fissures. Where paths exist across pavement, they exist for both reasons.

Worth knowing before you go — the specific injury is a leg dropping into a concealed fissure at walking pace, because grasses and ferns close over the top of a grike and give no warning whatever, which is why crossing pavement is slow work even for people who do it often.

Where to see it

Extensive pavements occur in the Yorkshire Dales, the Burren in Ireland and parts of the Alps and Scandinavia. The Burren is unusual in combining Arctic, Alpine and Mediterranean plants in one place, on the same rock.

Over a season, late spring is the best time for the flora in most of these areas. The best-known pavements are also the most visited, and on those the damage now comes from footfall and from stone lifted to build shelters and cairns rather than from lorries — a smaller problem working on rock that still does not recover.

The exception is usually weather, which overrides most planning.

Limestone country has almost no surface water

Rain sinks into the joints instead of running off, so a limestone upland can take heavy rainfall and still offer no stream to fill a bottle from all day. The water reappears at springs and risings, usually where the limestone meets an impermeable bed beneath it, and those points are marked on good maps and are worth planning a day around. Because that water moves through open fissures rather than filtering slowly through soil, surface contamination reaches the springs quickly and largely untreated, which makes limestone catchments unusually sensitive to slurry, septic discharge and livestock.

The detail that matters: the same fissures produce sinkholes and shakeholes, which in vegetated country are concealed, unfenced and deep enough to matter — a particular hazard in mist, on ground that otherwise looks like ordinary pasture.

Everything above, in order of what to do first

1. How it forms. Glaciers stripped the soil from horizontal limestone beds, exposing bare rock.
2. The fissures are the habitat. Grikes are humid, sheltered and shaded, producing conditions closer to woodland than to open hillside.
3. Removal was industrial. Large quantities were lifted and sold as weathered garden rockery through the twentieth century.
4. Walking on it. The surface is slippery when wet and the grikes are deep enough to break a leg.
5. Where to see it. Extensive pavements occur in the Yorkshire Dales, the Burren in Ireland and parts of the Alps and Scandinavia.
6. Limestone country has almost no surface water. Rain sinks into the joints instead of running off, so a limestone upland can take heavy rainfall and still offer no stream to fill a bottle from all day.

The takeaway

Look into the fissures rather than across the surface. That is where the habitat lives.

What holds up over a week outdoors is rarely what looks best at the trailhead.