Cryptogam- and annual-dominated vegetation on siliceous rock outcrops

These open pioneer grasslands occur on shallow soils (Leptosols) at rock outcrops, on eroded slopes, or in disturbed patches within dry or mesic grasslands. Stands are usually of limited extent, in many cases occupying just a few square metres. This vegetation is dominated by vernal therophytes of the genera Cerastium, Myosotis, Veronica and others and succulent plants of the genera Sedum or Sempervivum (inclusive Jovibarba). Hemicryptophytes are also common, especially the narrow-leaved tussock-forming species of Festuca and several xerophilous Poa species, but they are not the dominant component of this vegetation, except for some short-growing species such as Scleranthus perennis. Geophytes such as Gagea sp. pl. also occur in places. The richness of therophytes and geophytes increases when moving from northern and western to southeastern Europe. Bryophytes and lichens are also common and they can attain a very high cover in some places. Mosses are represented for example by Ceratodon purpureus, Polytrichum piliferum and Syntrichia ruralis agg., lichens by Cetraria aculeata, Cladonia sp. pl. and Xanthoparmelia sp. pl.

Shallow soils supporting this vegetation are well drained and dry out quickly, especially during summer periods of warm weather. Therefore vegetation has its phenological optimum in spring when moisture is still available due to lower evaporation rates. Most therophytes complete their life cycle within a short period of a few weeks prior to the peak of the seasonal development of hemicryptophytes, which helps them avoid competition for light. In contrast, most succulents are perennial and adapted to enduring summer drought period. However, they are more sensitive to disturbance, therefore more disturbed sites tend to contain more therophytes and less disturbed sites more succulents.

This vegetation is distributed throughout temperate and boreal Europe, but it is rarely found in extensive stands. It occurs across a broad altitudinal range from the lowlands to the subalpine belt. The type corresponds to the phytosociological order Sedo-Scleranthetalia, including the Sedo-Poetalia glaucae, which is by some authors separated as an order that occurs from the middle boreal to the arctic zone. Phytosociological literature distinguishes several alliances confined to different European regions, which are geographical vicariants with distinct species composition. A specific subtype of this habitat is found in the supratemperate, very humid belt of Madeira (over 1400 m a.s.l.), where Thymus micans dominates open pioneer communities on shallow soils and rocks, derived from hard volcanic substrate. Another specific subtype occurs on and around acidic outcrops in middle and northern Fennoscandia and Iceland (the Veronico-Poion glaucae).

Indicators of good quality:

These grasslands are confined to stressed or disturbed sites. Due to their small spatial extent, individual stands can be entirely destroyed, but they can regenerate if suitable conditions return. Sites on the rock outcrops near lookout points can be negatively affected through frequent trampling by tourists. On the other hand, disturbance-dependent stands occurring in patches among closed grasslands may become overgrown by tall perennial species if disturbance (e.g. grazing) ceases. Therophytes typical of this vegetation can also occur in human-made habitats such as roadsides, railway banks or quarries, where they form communities with ruderal and nutrient demanding species; such sites are not included in this habitat type and are of lower conservation interest.

The following characteristics can be considered as indicators of good quality:

·      Long-term habitat stability

·      High species richness of therophytes and succulents

·      Occurrence of rare species

·      Dependence on naturally stressful conditions or natural disturbance rather than human-induced disturbance

·      Absence of tall, nutrient-demanding and ruderal species

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats