Encyclopedia of Islands

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Biogeography and ecology of Canary Islands

The Canary Islands have an area of 7447 km2 and are located close to the northwestern Saharan coast (∼28° N latitude and 16° W longitude). They are composed of seven volcanic islands and a few islets. Several environmental factors contribute to the ecological peculiarities of these islands including the heavy infl uence of the cold Oceanic Canary current and the northeastern trade winds, the altitude (the highest mountain of Spain, Peak Teide [3718 m], is located on Tenerife, the occasional dry winds from the Western Sahara, the high elevation anti-trade dry winds from tropical latitudes, and a topography highly dissected by volcanoes, steep cliffs, caves, and deep gorges and gullies. The archipelago has never been connected to the mainland; however, during the last ice age, Lanzarote and Fuerteventura collectively formed one large island. Quaternary sea-level changes have also infl uenced the biogeography of the archipelago.

Biogeography and ecology of Canary Islands

It is likely that several “sea mountains” located between the Canaries and Madeira/the mainland were exposed during glacial periods and served as stepping stones for dispersal of faunal and fl oral elements. Fossil beaches located a few meters above the coastline provide further evidence for a changing topography caused by fl uctuations in sea level.

The Canary Islands and four additional volcanic archipelagoes (i.e., the Azores, Madeira, the Selvagens, and Cape Verde) form the Macaronesian Islands. There has been a long debate on whether these archipelagoes should be considered a distinct biogeographical unit. Macaronesia as a biogeographical entity is supported by the many plant genera and species that are endemic to more than one archipelago. In addition, several evolutionary lineages (clades) with considerable numbers of species are shared across some of these archipelagoes. Opponents of a single biogeographical unit contend that major bioclimatological differences among the archipelagoes support the Canary Islands and Madeira fl oras belonging to the
Mediterranean region, whereas the fl oras of the Azores and Cape Verde are part of the Medioeuropean and Sudano-Zambesian regions, respectively.

The Canarian biota has been the focus of several phytosociological and bioclimatological studies, and fi ve major terrestrial ecosystems, or life zones, can be recognized. The coastal thicket—low elevation arid woodland (Kleinio-Euphorbietea canariensis) is present in all the islands at low altitude (0 to 400 m on southern slopes, and a predominant coastal distribution on northern slopes [Fig. 2]). This zone is devoid of large trees and is mostly fi lled with small shrubs and perennial plants with succulent leaves and stems (e.g., Euphorbia spp., Kleinia neriifolia, Ceropegia spp., Aeonium spp., Plocama pendula) or coriaceous leaves (e.g., Rubia fruticosa, Cneorum pulverulentum, Echium spp.). Annual rainfall in this zone is below 250 mm.

Dry sclerophyllous forests (Rhamno crenulatae–Oleetea cerasiformis) occur between 400 and 600 m (on southern slopes) and between coastal areas and 600 m (on northern slopes) on all islands. This plant community receives an average annual rainfall of 400 mm and has strong fl oristic links to the Mediterranean Thermophile forests, with those on northern slopes being fl oristically richer than those on southern slopes. Indicator plants for this ecosystem include trees such as Olea europaea subsp. guanchica, Dracaena draco, Juniperus turbinata subsp. canariensis, Pistacia atlantica, Visnea mocanera, Phoenix canariensis and small shrubs such as Cheirolophus spp., Crambe spp., Echium spp., Rhamnus crenulata, and Sid-
eritis spp. The humid evergreen forests (Pruno hixa–Lauretea novocanariensis) are restricted to those slopes of the islands that face the northeast trade winds and are located between 600 and 1200 m. These forests, known as “laurel forests” because they are characterized by several tree species (i.e., Apollonias barbujana, Laurus novocanariensis, Ocotea foetens, and Persea indica) in the plant family Lauraceae, are usually cloud covered (average annual rainfall 800–1000 mm), with moisture levels enhanced by the extensive condensation of moisture on leaves, a phenomenon locally known as lluvia horizontal (“horizontal rain”). The humid evergreen forests are not found on the most easterly islands of Fuerteventura
and Lanzarote, although some small pockets were likely present in Fuerteventura prior to the arrival of European settlers.

The fourth life zone is the Canary pine forest (Chamaecytiso–Pinetea canariensis alliance Cisto–Pinion canariensis). The only species of pine present in the islands, the endemic Pinus canariensis is the representative plant element of this zone. This vegetation type is also absent in Lanzarote and Fuerteventura, and has few small natural pockets on the island of La Gomera. This forest occupies northern (1200–2000 m) and southern (600–2300 m) slopes (average rainfall 200–800 mm).
A transitional zone, known locally as Fayal-brezal (Andryalo–Ericetalia arboreae), occurs between the laurel and pine forests. Two trees, “brezo” (Erica arborea) and “faya” (Morella faya) are the predominant plant species of this zone.
Finally, a fi fth life zone is a high-elevation dry woodland (Chamaecytiso–Pinetea canariensis alliance Spartocytision supranubii) and is confi ned to slopes over 2000 m on La Palma and Tenerife (average annual precipitation 400 mm, most as snow). During winter, frosts are common. Currently, this vegetation type has the shrubs Adenocarpus viscosus (on La Palma) and Spartocytisus supranubius (on Tenerife) as dominant species, and several endemic species such as Echium wildpretii. However, in the past, this was an open forest where the “cedro canario” tree (Canary Island juniper, Juniperus cedrus) was an important species. This species was almost driven to extinction because it was extensively used for timber.
Today, the Canary Island juniper is almost a memory on these islands and is mostly relegated to inaccessible landscapes on La Palma.

The humid evergreen forest has the highest number of endemic plants, invertebrates, and vertebrates. However, the two ecosystems with the lowest plant species diversity, the coastal thicket, low-elevation arid woodland and the dry, high-elevation open woodland, also possess an endemic fl ora/fauna adapted to their ecological peculiarities. For instance the endemic beetle Lepromoris gibba feeds exclusively on succulent species of Euphorbia restricted to the coastal thicket. Likewise, the praying mantis Pseudoyersinia teydeana is only found on highelevation ecosystems of Tenerife. Concerning vertebrates, the coastal ecosystem has an endemic mammal (the Canarian shrew, Crocidura canariensis) restricted to Fuerteventura and Lanzarote, and an endemic bird (the Canary Islands stonechat, Saxicola dacotiae) confi ned to Fuerteventura. There are no endemic vertebrates in the dry, high-elevation woodland, although both the “pinzon azul del Teide” (Teide blue chaffi nch, Fringilla teydea) and the “murcielago orejudo” (long-eared bat, Plecotus teneriffae) are found in this ecosystem and in the pine forest.