Today the whole island of La Palma is under the status of a UNESCO biosphere reserve, after initially in 1983 the laurel forest of Los Tilos was established as a first biosphere reserve, which was the first on all Canary Islands. It is an outstanding fact that in this reserve a complete terrestrial surface is protected including large surfaces of absolutely pristine ecosystems and a legacy of human influenced habitats. Since 2011 the island represents the first UNESCO starlight reserve worldwide. The central part of the island is preserved as a national park “Caldera de Taburiente” established as early as 1954.
With 87.000 inhabitants in total on more than 700 km2, population density is low on the island. In addition, large parts are simply inaccessible and unfavourable for human settlements. Tourism and agriculture (bananas and other crops) are the main income. Thus, nature is the most valuable resource of the island.
La Palma is the northwestern island of the Canary Islands, positioned in the Atlantic Ocean off the coast of northwestern Africa (Fig. 1). La Palma is a relatively young volcanic island reaching an age of roughly 1.7 Ma (Carracedo et al. 2002). The maximum elevation measures 2426 m, the area 708 km2 (Carracedo et al. 2002). Climatically, La Palma is a ‘mini-continent’ exhibiting a subtropical climate with not very pronounced seasonality but moist winter and dry summer (Garzón-Machado et al. 2013). But, the climatic conditions differ considerably within the island.
Annual precipitation ranges from about 170 mm to almost 1400 mm, annual temperature from about 9 to around 22°C (Irl & Beierkuhnlein 2011). These strong differences are not only related to the altitudinal gradient. La Palma is strongly influenced by the trade winds blowing from the Northeast. This creates a climatic divide of the island. The windward side is generally more humid receiving the most precipitation and higher cloud cover, while the leeward side is dryer and has more insolation. La Palma is the most humid island of the Canarian archipelago.
However, above the trade wind-induced cloud zone a thermal inversion layer exists, generally exhibiting dry conditions and possessing the possibility of snow and ice in winter (García-Herrera et al. 2001).
The vegetation zones directly follow the climatic gradients (Fernández-Palacios & de Nicolás 1995). These zones range from halophytic communities in arid coastal areas to succulent scrub and thermophile woodlands in semi-arid lower elevations, over the endemic Canary Pine forest in mid elevations to a high-elevation summit scrub. On the windward side a palaeo-endemic evergreen humid laurel forest and a slightly less humid tree heath-Morella faya forest exist at mid elevations in the zone of the trade wind clouds instead of the Canary Pine forest (del Arco-Aguilar et al. 2010, Garzón-Machado et al. 2013).
According to Acebes Ginovés et al. (2010) La Palma possesses 37 single island endemic plants (which is an underestimated number as various scientifically un-published species are known, 210 archipelago endemics to the Canary Islands).
The Caldera de Taburiente National Park (Parque Nacional de La Caldera de Taburiente), is located on the island of La Palma in the archipelago of the Canary Islands, Spain. This park ranges between 250 and 2426 m a.s.l. Large areas of the park are simply inaccessible due to steepness and instable rocky substrates. This supports natural processes and reduces the influences of visitors to narrow margins of the very few paths through the park. However, the restricted access to the ecosystems also avoids precise mapping and field work. Sophisticated remote sensing and modelling approaches are urgently required due to the extreme three-dimensional structure of the surface.
The park is dominated by endemic plant species. Especially, the vegetation is characterised by a high percentage of endemics and especially single island endemics. Recently, even plant species that are new to science were found in the national park. Europe has the responsibility to safeguard this biological heritage.
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This park is one of the very few examples of untouched and pristine ecosystems within the whole area of the European Union. These ecosystems are unique but also characteristic for islands. Large areas are covered by Canary Pine forest (Pinus canariensis). In the deeply incised gorges and valleys, flowing water exists all year that is supported by permanent springs. This is unique for the Canary Islands.
Along these brooks and rivers in the Barranco de los Angustinos, Canary Willow (Salix canariensis) woodlands exist, where Pericallis papyracea is frequent.
In the summit area, single island endemics that do not exist in other places of the world are frequent. Following species are remarkable and unique: Genista benehoavensis, Adenocarpus viscosus ssp. spartioides, Echium gentianioides, Echium wildpretii ssp. trichosyphon, Descurainia gilva, Arrhenatherum calderae, Viola palmensis. The rocky outcrops are occupied by a large set of island endemic species (e.g. Aeonium palmense, Aeonium nobile, Aenonium davidbramwellii, Senecio palmense, Tolpis calderae). In the shady and moist places relicts of the tertiary flora such as Woodwardia radicans are to be found. The forest ecosystems are strongly influenced by natural wildfires. Species such as Pinus canariensis or Cistus symphitifolius are perfectly adapted to these disturbances. However, Europeans have introduced non-native invasive herbivores (rabbits, goats, rats) that have caused severe damage to the sensitive vegetation since centuries. Here again, novel approaches for restoration and preservation are urgently needed. Furthermore, the extraction of water from this catchment for irrigation purposes, which is based on traditional regulations, is a challenge for nature conservation, but sound data on the impacts of this uses are missing.
The national park area is of high importance for cultural aspects, too. This was the site where the last tribe of the native Guanche people survived, using the steep slopes of the caldera as a national fortress. Artefacts and sacred places of this culture exist in the national park. The geomorphological shape of the crater-like structure is the locus typicus for the term “caldera” which was given to this specific landscape by Leopold von Buch at begin of the 19th century. However, it turned out much later that the caldera structure on La Palma was created mainly by erosion and not by the collapse of a magmatic chamber.
In general, island ecosystems are known to be extraordinarily sensitive to human impact. Europe has the responsibility to protect these ecosystems that are of global importance. La Palma still hosts natural ecosystems and a large series of endemic species. In contrast to other European islands such as the Azores, invasion processes are still of low importance. However, the steep slopes and the moist climate make it impossible to access major parts of the island. Remote sensing approaches are urgently needed, here!
References
Irl, SDH; Steinbauer, MJ; Babel, W; Beierkuhnlein, C; Blume-Werry, G; Messinger, J; Palomares-Martínez, A; Strohmeier, S; Jentsch, A: An 11-yr exclosure experiment in a hgih-elevation island ecosystem: introduced herbivore impact on shrub species rechness, seedling recruitment and popluation dynamics, Journal of Vegetation Science, 23, 1114-1125 (2012)
Irl, S; Steinbauer, M; Epperlein, L; Harter, D; Jentsch, A; Pätz, S; Wohlfahrt, C; Beierkuhnlein, C: The hitchhiker's guide to island endemism - biodiversity and endemic perennial plant species in roadside and surrounding vegetation, Biodiversity and Conservation, 23, 2273–2287 (2014)
Steinbauer, M; Beierkuhnlein, C: Characteristic Pattern of Species Diversity on the Canary Islands, Erdkunde, 64(1), 57-71 (2010)
Steinbauer, M; Dolos, K; Field, R; Reineking, B; Beierkuhnlein, C: Re-evaluating the general dynamic theory of oceanic island biogeography, Frontiers of Biogeography, 5(3), 185-194 (2013)
Steinbauer, M; Otto, R; Naranjo-Cigala, A; Beierkuhnlein, C; Fernandez-Palacios, JM: Increase of island endemism with altitude – speciation processes on oceanic islands, Ecography, 35, 23-32 (2012)