Canarian mountain hedgehog-heath

Canarian high-mountain volcanic semi-desert scrub, restricted to the subalpine zone of Tenerife and La Palma. The main occurrence of this rare and unique habitat type concerns the Cañadas del Teide on Tenerife, where it covers several square kilometers of the comparatively flat bottom of this huge caldera, one of the largest in the world. The dominant shrub species here is the striking hemispherical ‘hedgehog’ species Cytisus supranubius (up to 2 m), accompanied by a set of smaller species from different plant families showing a similar growth form, e.g. Nepeta teydea (Lamiaceae), Pterocephalus lasiospermus (Dipsacaceae) and Descurainea bourgeana (Brassicaceae). Every year, during its flowering period in May, Cytisus supranubius is painting the lava landscape in a bright white, in honor of its Spanish name ‘retama blanca’. Another prominent species in this open habitat is the pillar-shaped Echium wildpretii, which appearance reminds us of the Senecio and Lobelia communities in the arid belt of East-African tropical mountains above the timber line. The caldera is situated above 2,000 m and almost never gets any precipitation. It is thought that the dead remains of the flower stalks of the various species are able to catch and transport water during periods with fog. In addition to the limited supply of water, the extreme soil conditions strongly determine plant growth in this bare volcanic landscape.

The habitat type further comprises two scree communities at the summits of the Canaries, one on Tenerife and one on La Palma. On Tenerife, Viola cheiranthifolia is found on the flanks of the Teide, above the caldera, and on La Palma, Viola palmensis is growing in the highest parts of the island. Both the hedgehog and the scree communities are permanent natural vegetation.

This mountain habitat type is of particular conservation value as it houses a set of endemic and extremely rare species, which even do not (or hardly) occur outside the range of the habitat. Another conspicuous feature is that these communities do not support the occurrence of more widespread species, as is the case in other endemic ecosystems. Where the endemic habitat types of the Canary Islands at lower altitude are generally accompanied by many mediterranean species, this is not the case in these high-altitude hedgehog and scree communities. As a consequence, the habitat type is rather poor in species (5-10 species in general).

Indicators of good quality:

• Presence of rare and endemic species.
• Absence of ruderal, often more nutrient-demanding species.
• Absence of alien species (grasses and shrubs).
• Long-term habitat stability, with no successional trends.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats