Flora of the Canary Islands. Vegetation zones. Humid thermocanarian zone. Flora and vegetation of the Canary Islands

Zone termocanario damp

    The humid Canarian forest, also known as the laurisilva or monteverde, is found at altitudes of between 800 and 1,200 metres on the north-facing slopes of the highest islands, which are under the influence of the humid north-easterly trade winds for most of the year, and, exceptionally, in small areas in the south and west of the islands, such as Cumbre Nueva on La Palma and the Güímar slope on Tenerife.
     These trade winds do not bring rainfall, but as the moist air rises up the slopes, it condenses and forms a vast cloud mass known as a sea of clouds. Under these conditions, sunlight is greatly reduced, temperatures become milder, and moisture is trapped by the dense vegetation, which acts as a sort of ‘sponge forest’, providing a water supply that can be up to three times the annual rainfall. Due to their age and the effects of the climate and vegetation, the soils are generally highly developed, with great depth and a well-defined organic topsoil layer, as the high humidity and temperate temperatures lead to rapid humification and mineralisation of leaves and other plant debris that have fallen to the ground, releasing abundant nutrients that are rapidly absorbed by the roots.
    In this very special habitat, the laurel forest thrives – an evergreen, predominantly tree-dominated woodland formation whose vast mass of leathery, glossy leaves promotes the condensation of moisture contained in the mists that almost constantly shroud the area, producing a slow, fine and almost constant local rainfall at the foot of each tree, known as ‘horizontal rain’.

This type of forest was widespread throughout the Mediterranean basin, North Africa and southern Europe during the Tertiary period (around 20 million years ago), but the climatic changes that have occurred since then – including ice ages and arid periods that gave rise to the desert barrier of North Africa – led to the disappearance of this vegetation from the continents, finding refuge in the Macaronesian archipelagos (the Azores, Madeira and the Canary Islands), as the influence of the ocean acts as a thermostat regulating environmental conditions; consequently, the present-day Canarian laurel forest formations are nothing more than relics of those ancient Mediterranean forests. In the archipelagos of Madeira and the Azores, a more favourable climate allows them to occupy a larger potential area and to be found at lower altitudes, even almost at sea level, whilst also exhibiting a different floristic composition to that of the Canary Islands.
The present-day laurel forests represent the optimal vegetation in the wettest areas of the Canary Islands. In Gran Canaria, they reached their maximum extent above 600 m, although in the ravine basins they could grow at lower altitudes. In Tenerife, El Hierro and La Gomera, they occur from 400–500 metres upwards, whilst in La Palma, due to more favourable climatic conditions, their preferred altitude range is between 300 and 500 metres, with the lowest elevations found in the northern part of the island, on the slopes and in the ravines of Barlovento and Garafía.

Externally, they are characterised by their appearance as a vast, compact green mass, with a wide range of shades and, seasonally, yellow or reddish hues. Their vegetation is highly diverse and stratified, although the tree layer stands out, consisting of a group of large, beautiful and hardy trees that reach an average height of around 10–15 metres. Due to the limited light that filters through the tree canopy, the shrub layer is rather sparse, whilst a layer of large ferns stands out, sometimes so dense that it is difficult to pass through.

The most characteristic tree species of the laurel forest are the laurel (Laurus novocanariensis), the barbusano (Apollonias barbujana), the tilo (Ocotea foetens) and the viñátigo (Persea indica). Other large tree species are also common, such as the Canary Island holly (Ilex canariensis), the wild orange (Ilex perado, spp. platyphylla), the aderno (Heberdenia excelsa), the delfino (Pleiomeris canariensis), the mocán (Visnea mocanera), the hija (Prunus lusitanica), the sanguino (Rhamnus glandulosa), the palo blanco (Picconia excelsa), the madroño (Arbutus canariensis), the heather (Erica arborea) and the faya (Morella faya).
Epiphytic plants are common on the trunks and branches of trees, particularly in damp, shady areas; these plants live on the tree, using it solely as a support, without being parasites in any way. Examples include the golden star (Aichryson laxum) and the Christmas fern (Polypodium macaronesicum), etc.

Arbutus canariensis

In the more open and sunny areas, as well as along the edges of paths and forest tracks, there is an abundance of subshrubs and herbaceous plants, such as cock’s comb (Isoplexis canariensis), bicácaro (Canarina canariensis), follao (Viburnum rigidum), tree starflower (Gesnouinia arborea), algaritofe (Cedronella canariensis), Canary Islands bindweed (Convolvulus canariensis), white bush (Pericallis appendiculata), mountain queen (Ixanthus viscosus), mountain chahorra (Sideritis macrostachys), the Morgallana (Ranunculus cortusifolius), the ‘pata de gallo’ (Geranium reuteri), the mountain pennyroyal (Bystropogon canariensis), the ivy (Hedera canariensis), the gibalbera (Semele androgyna), the sarsaparilla (Smilax canariensis), etc. The genus Euphorbia, typical of xerophilous and semi-xerophilous areas, is represented in a unique way in the laurel forest: the mountain oleander (Euphorbia mellifera), a true rarity that is seriously threatened with extinction.
Notable ferns include large species such as the wood fern (Woodwardia radicans), the mattress fern (Culcita macrocarpa), the hairy fern (Polystichum setiferum), and the mountain ferns (Dryopteris oligodonta and Diplazium caudatum), etc.

Cedronella canariensis

The laurel forest once covered a vast area of woodland in the central and western Canary Islands. Intensive exploitation from the very outset of the Conquest (for charcoal, timber, land clearance, etc.), which has continued uninterrupted to the present day and has intensified at certain times, has led to the near disappearance of the pure stands of this incredibly rich forest. Its destruction can be considered almost total in Gran Canaria, as the remaining areas are now merely small, heavily altered remnants of what were once splendid forests, stretching from the vicinity of Valsequillo, across the whole of the north, to Agaete. Its greater extent, combined with less exploitation, has allowed for a more favourable state of conservation on the other western islands.

When the mist caused by the trade winds begins to clear – due to greater altitude or a change in the north-south aspect of the slopes – environmental conditions gradually change: air and soil humidity decrease, the amount of sunshine increases, and strong winds are quite common. These factors lead to the gradual disappearance of the laurel forest and the emergence of a new plant community, directly related to the former but with its own distinctive characteristics. This is the fayal-brezal, a woodland formation situated in the transition zones between the humid, warm areas of the laurel forest and the cooler, xerophytic areas of the pine forest.

     This forest type thrives at altitudes of between 500 and 1,000 metres, on north- and north-east-facing slopes, although in some areas it can reach altitudes of up to 1,700 metres above sea level. In many cases, the fayal-brezal forest occupies the most degraded areas of the laurel forest and pine forest, either as a result of fires or, more frequently, due to excessive logging carried out in the past. These forests are generally very difficult to navigate, as their shrub layer is very dense and their undergrowth is very tangled.
    At present, the finest examples of fayal-brezal are found in Hermigua and Agulo on La Gomera; Las Mercedes and Anaga on Tenerife; the eastern slope of Cumbre Nueva on La Palma; and the peaks of El Golfo on El Hierro.
     In the beech-heath forest, the species are less demanding than in the laurel forest and have a wider ecological range, forming a more open forest type with less species diversity; the tree layer is dominated by the beech (Morella faya), tree heath (Erica arborea) and yew (Erica platycodon), with the Canary Island holly (Ilex canariensis) and the laurel or ‘loro’ (Laurus novocanariensis) occurring less frequently.
    Furthermore, isolated occurrences of some species typical of the less humid areas of the laurel forest can be found, such as the whitewood (Picconia excelsa), the barbusano (Apollonias barbujana), the mocán (Visnea mocanera), the strawberry tree (Arbutus canariensis), the sanguino (Rhamnus glandulosa), the palo blanco (Picconia excelsa), the hija (Prunus lusitanica spp. hixa), etc.

The undergrowth is very species-poor, as the dense canopy of the fayal-brezal allows little light to reach the ground. Among the herbaceous and shrubby species that can be found in the more open areas are the wild blackberry (Rubus ulmifolius), the large-leaved St John’s wort (Hypericum grandifolium), the Montpellier rockrose (Cistus monspeliensis), the tree-leaved Gesnouinia (Gesnouinia arborea), the stiff-stemmed viburnum (Viburnum rigidum), the sneezewort (Andryala webbi), the paper-leaved Pericallis (Pericallis papyracea), the mountain violet (Viola riviniana), etc. Two ferns are also commonly found: Pteridium aquilinum and Asplenium onopteris.