Limestone pavement

Limestone pavements are geomorphological landscapes resulting from dissolution processes exerted on hard limestone tables probably formed by glacial erosion. They consist of usually gently-sloping platforms with blocks of limestone separated by a network of vertical fissures. The size, shape and regularity of the blocks vary according to the local features of the bedrock and of the climate, but the regular mosaic of contrasting microhabitats is a common feature to all limestone pavements. This unit has a purely geomorphologic definition. It occurs from sea level up to 3000 m  in the Alps and extends to a wide range including different karstic regions of Europe, where it receives different local names: lapiaz, karren, limestone pavement, alvar. This specific geomorphology is apparently linked to glacial origins. Karstic outcrops occurring in the Mediterranean region are often less typical. Only large tabular surfaces showing typical dissolution features come into consideration for habitat H3.5a.
The rock surface of the pavement is almost devoid of soil, with a resulting vegetation cover well under 30%. Spots of thin soil allow locally the presence of drought-resistant communities: cushions of lichens and bryophytes, fragments of dry tufted grasslands.  Most of the vascular plants root in the fissures, where rubble and fine sediment, including aeolian and organic matter, accumulate, sometimes also the long-weathered remnants of pre-Quaternary deposits. These fissures (called grikes or Kluftkarren) offer a sheltered microclimate, favoring ferns and macroforb communities; heath and scrub can also occur (wooded pavements belong to other units). Espaliered plants, with their stems expanding at the rock surface, are also a typical component of the mosaic but exposure to wind and grazing by wild herbivores or farm stock may limit expansion of vegetation from the fissures. 
According to the diversity of climates encountered in the large range of this unit, the floristic composition is variable and not very helpful for the identification: the communities occurring in the pavement mosaic are not the same in the Alps as in Britain. Anyway, none of those communities is unique to limestone pavements. What is characteristic is the pattern of contrasting microhabitats, and the resulting mosaic of small patches of different vegetation types.

Indicators of good quality:
Typical limestone pavements are large and uniformly level, sub-horizontal tables of blocks made of unfragmented frost-resistant hard stone. The vegetation covers less than 30%. Trees are absent or very scattered. Limestone outcrops of small extent (less than 1000 m²) or not showing the typical pattern are excluded. This habitat does not recover after quarrying and other extractive activities.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats