Boreal ultramafic inland cliff

Boreal ultramafic inland cliffs are habitats which host unique serpentine plant communities. The concept ultramafic refers to rock types that have a low content of silica and rather high content of magnesium and iron. This kind of rock, in particular serpentinite, produces extreme edaphic conditions with low calcium-to-magnesium ratio, severe scarcity of essential nutrients such as nitrogen, potassium, and phosphorus, and often also high levels of heavy metals such as nickel, chromium or cobalt. As a consequence of these chemical conditions, vegetation is often very scarce with large spots of bare rock. As an adaptation to harsh environment some species have developed morphological features of dry site plants.

Some plants have adapted to these harsh conditions. In the Boreal region, this group includes Arenaria pseudofrigida, Asplenium adulterinum, A. viride, Cerastium alpinum, C. fontanum ssp. vulgare, Dianthus superbus, Minuartia biflora, Sagina nodosa and Viscaria alpina var. serpentinicola. In addition to these special plants, some common plants also grow in serpentine environments, e.g. Calluna vulgaris, Juniperus communis, Deschampsia flexuosa, Festuca ovina and Sedum telephium.

Bryophyte and lichen communities of serpentine cliffs often show a special mixture of calciphilous and other species. Typical bryophytes include Campyliadelphus chrysophyllus, Encalypta streptocarpa, Sanionia uncinata, Schistidium apocarpum coll., Tortella tortuosa and Weissia controversa, but in contrast to calcareous cliffs they do not form luxuriant turfs. Both bryophyte and lichen vegetation cover is generally lower than on other kinds of rocks and large areas on rock walls are entirely unvegetated.

The relationship between serpentine plant communities and rock types is under discussion. All ultramafic rock types do not host distinct serpentine plant communities. For example, communities on unchanged peridotite usually resemble those of ordinary siliceous cliffs more than serpentine cliffs.

Ultramafic cliffs with serpentine plant communities occur from the lowlands of eastern Finland to the middle alpine zone of the Scandinavian mountains. Two vegetation types have been recognized: the more widespread Asplenium viride – Arenaria norvegica–type (with a variant without A. norvegica in the eastern parts of the region) and the oceanic Asplenium adulterinum–type.

Indicators of good quality:

• bedrock intact (no quarrying)
• presence of natural disturbance regime (relevant especially in forested areas: forest fires are prevented, which means that vegetation coverage is slowly increasing; on the other hand, intensive forestry and particularly clearcutting causes abrupt changes in microclimate, which destroy plant communities adapted to stable humid conditions)
• absence of alien species

The species diversity varies enormously also in entirely natural communities in cliff habitats. Usually, the smallest rock formations with monotonous microtopography and little variation in rock types show low diversity, whereas larger cliff complexes with heterogeneous geomorphology and varying rock types may represent local biodiversity hotspots. Therefore, low species diversity or absence of rare species should not be interpreted by itself as an indicator of low habitat quality, unless it is caused by anthropogenic influence.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats