Garajonay - Can the Laurisilva preserve the Canary Island La Gomera from desertification?

Botany | Biodiversity | Climate Change

Doris Elster, | 28/03/12 | Bremen, Germany

(Image: Grajonay National Park; Source: Werner Weichhardt) “La Gomera, is round, even beautiful and, of all the islands it is the most agreeable to the eye, because in addition to its benign and happy sky, it is full of rolling hills, valleys clad with thick jungle which, enjoying an eternal summer, never lose their leaves.” (Leonardo Toriani, 16th century) La Gomera is one of the small western islands of the Canary Archipelago, situated between Tenerife and La Palma. The island is of volcanic origin, created by different eruptive phases which were separated by calm phases in which the natural forces of water-erosion have left their mark. That led to the development of a unique landscape, with high mountains, remains of volcanic vents, and deep valleys and canyons. Garajonay – UNESCO World nature heritage The Garajonay National Park is situated in the central highland of La Gomera. It encloses 4,000 ha and it contains and protects a unique forest eco-system, the Canary Laurisilva, which originally thrived in the mist-filled zones of the mountainous western Canary Islands.  Laurisilva – Jungle in the “sea of clouds” The Laurisilva in the Garajonay National Park is one of the most unusual eco-systems on earth. It is a type of forest or woodland made up of various species of evergreen trees whose leaves bear a certain similarity to those of the laurel tree and which needs a high level of humidity and mild temperature in a year-round pattern marked by low fluctuation. Laurisilva is typically surrounded by a sea of clouds. Due to the mist the local temperature in the Laurisilva tends to be between 13 and 16 degrees, whereas in some other part of the island the temperature climbs up tol 30 degrees at midday. Historical development Laurisilva eco-systems are genuine “living fossils”, the remains of subtropical forests which once grew along the coasts of the Mediterranean Sea, some millions of years ago in the Tertiary period. The subtropical forests disappeared from the continent as a result of climate change caused by the ice ages. Nowadays we find relicts only on the Atlantic islands (Azores, Madeira, Canary Islands). Garajonay National Park is one of the biggest recent Laurisilva eco-systems. It is important because of the ecological complexity and the extraordinary wealth of endemic species. In addition, it is one of the few remaining jungles in Europe. The word “jungle” conveys the idea of a forest which is basically intact or barely modified by human intervention, where various species of trees mix to form a thick canopy; it is an accumulation of biomass. A jungle is marked by the presence of different layers, with the largest and oldest trees forming the upper layer, and the presence of an accumulation of dead matter untouched by humans. Biodiversity in the Laurisilva The most commonly found species of trees in the Laurisilva are the following, in order of the frequency in which they occur: Erica arborea (heath) Myrica faya (bog myrtle) Ilex canariensis (acevino) Laurus azorica (laurel) Persea indica Picconia excelsa (Palo blanco) Other species are less common. Among these are the following: Erica scoparia (yew) Ocotea foetens (til tree) Apollonias barbujana (barbusano) Visnea mocanera (mocan) Arbutus canariensis (strawberry tree) Rhamnus glandulosa (buckthorn) Additionally, we have to mention the high number of mosses and lichens, which cover the barks of the trees as well as the thick cover of ferns, which can flourish due to the high humidity. Climate or Where does the mist come from? The Canaries are subtropical oceanic islands lying off the western coast of Africa. Their climate is essentially Mediterranean, in other words, there is a long dry period and the rainfall is highly irregular and tends to be concentrated into the months of autumn and winter. In addition, the temperature effect of the Atlantic gives rise to cooler summers and milder winters than in the continental areas at the same latitude. La Gomera is situated just in an edge where several different climatic systems meet and interact. The island is under the effect of the north-east trade winds, which, laden with humidity after their passage across the sea (coming from the Azores), reach the island. In the mountainous regions the body of air often reaches condensation point. That forms a layer of mist of varying thickness, which tends to remain stable over the northern peaks of the island. That causes the phenomenon known as “the sea of clouds”. The height of the “sea of clouds” varies from 600 to 1800 m and its thickness can range up to 500 m. The Laurisilva – an absorbent sponge The frequent presence of mists on the island’s mountain tops has a number of important ecological consequences: the low yearly sunshine and the high humidity rate limit the drying of the vegetation during the dry periods and supply plants with water in a phenomenon known as “horizontal rain”: the trees themselves generate a type of rain. They absorb the tiny drops of humidity carried by the mist, which in turn pass through the tree’s pores and when the branches are saturated they begin to drip and thus pass moisture to the soil. The significance of this phenomenon cannot be underestimated for such a predominantly dry island as La Gomera. This wetness feeds springs and although preserves deeper laying valleys with the life-giving water. What do you think? Has the Garajonay National Park the potential to prevent the desertification in La Gomera? Do you have ideas how to develop an IBSE task about the phenomenon of the “sea of clouds” (in dependence of temperature, wind, and sea level), the “horizontal rain” and plants (like mosses and lichens) working as absorbent sponges? Let us know your ideas? To read more about: References: Angel , Fernandez (2010). National Park Garajonay La Gomera. Visitors‘ Guide. La Gorma: Lerkoprint, S.A. Müller, A., Müller, T.K. (1996). Pflanzen auf La Gomera [Plants in La Gomera], La Gomera: Goldstadtdruck.


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