Boreal and arctic base-rich scree

This habitat type is connected to calcareous rock types, such as limestone, dolomite or calcareous siltstone. The habitat type extends from the southern boreal region to the arctic zone and harbours therefore large diversity of species and plant communities. Screes (or talus formations) are formed when rock fragments fall off from cliff faces as a result of physical and chemical weathering and erosion. Screes often show a sorting of rock fragments. The largest blocks roll down the furthest, whereas the finest material accumulates in the uppermost part of the slope. Most occurrences of this habitat type probably represent scree slopes but also flat baserich gravel or blockfields may have been formed by frost action breaking calcareous rock outcrops in situ.

Baserich or calcareous screes are distributed mainly in the Scandinavian Mountain range, Iceland and Svalbard. In Iceland the division between baserich and basepoor scree habitats is not as clear as elsewhere in northern Europe, but the species composition on more-or-less neutral screes fits best in the here described habitat type.  The sparsely vegetated flat, stony and sandy volcanic habitats of Central Island are included in type H5.1c.

Similar to siliceous screes, the vegetation of baserich screes varies in the boreal region from forests to scrubs and sparsely vegetated, unstable patches, if considered as a whole. However, the habitat type in question only refers to more or less open patches that do not have a tree or scrub layer. In screes, the most characteristic assemblages of vascular plants are found in the unstable patches, where also weak competitors or various pioneer communities can persist. On calcareous substrate, characteristic plants are Arenaria humifusa, A. norvegica, A. pseudofrigida, Artemisia norvegica, Papaver species of the Papaver radicatum group, Papaver relictum, Papaver laestadianum and Braya linearis.

The most important factor determining the species composition of screes is natural or seminatural disturbance regime, which maintains characteristic species assemblages. In screes, the disturbance regime is characterized by the continuum of periodic rockfall, unstability of the substrate, and in some regions also by the long tradition of grazing. In some cases, grazing or, e.g., hiking or mountaineering activities may cause additional erosion in the habitat to such an extent that it disturbs the formation of typical vegetation.

Indicators of good quality:

·      natural or seminatural disturbance regime, with a continuum of periodic rockfall and unstability of the substrate or (in some cases) forest fires

·      no or little succession towards scrub and forest

·      continuation of traditional grazing (where relevant)

·      no disturbance (for example by hiking, grazing, etc.)

·      diversity of lichen, moss and vascular plant species

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats