A Nature Travel Guide about a Fascinating Volcanic Island of the Canarian Archipelago
Buch, Englisch, 128 Seiten, PB, Format (B × H): 150 mm x 210 mm, Gewicht: 220 g
ISBN: 978-3-942999-09-0
Verlag: NATURALANZA
A nature travel guide with many impressive photographs, as well as detailed and well-founded information on the flora and fauna and their habitats. The majority of these are unique to Tenerife or the Canary Islands. The suggested excursions allow an experience of the sometimes bizzare natural phenomena found here. This book is a must for anyone with an interest in nature, as it fascilitates the discovery and understanding of the unusual biological diversity and beauty of this island.
Autoren/Hrsg.
Weitere Infos & Material
Table of Contents
Introduction 4
The golden apples of the Hesperides 6
Alexander von Humboldt: enthusiastic explorer of Tenerife 8
Volcanism and geology 9
Stone roses, organ pipes and Teide-eggs 12
On rafts, flying and as stowaways 14
One species results in many – the Galapagos of the Atlantic 16
Colourful viper’s buglosses 19
A biological window into the past 22
Giants and flightless creatures 24
The Habitats
Climate and biology 26
El Médano: Rocky shores, beaches and sand dunes 30
Life in the surf zone 32
Succulent shrub – “cacti”, ceropegias and
plants which can hold their breath 35
Thermophilic forest – few remaining fragments 40
Laurel forests – relics of a time past 41
Myrtle and heath forest – where Firetree and heath grow into the sky 46
Teno Alto – land of the Rock Sparrows 49
Pine forests – quiet whispering and heavenly peace 52
Barrancos – water and rock 55
The Teide National Park 59
Lava fields and caves 66
Animals and Plants
The Canary Dragon Tree 68
The late honour of Euphorbios 70
Ferns of the laurel forest: lovers of humidity 72
Towards the light – at the expense of others 74
Treacherous sex, traps and window flowers 75
Dragons, skinks and geckos 78
Einstein got it wrong: honey, wild- and bumble-bees 81
Butterflies – colourful diversity 84
Latex-sap, poison and butterflies 88
Deception, delusion and disguise 90
Birds – in the darkness of the laurel forest 92
Birds – on cones and trunks of the pine forest 97
Birds – in succulent shrub and the Cañadas 99
Birds – in settlements and farmland 101
Birds – on the shore 102
The Atlantic Canary 104
Flower birds – an acquired taste 106
Danger and Protection
Hostile takeover 108
Agricultural plants 111
The exotic – bottlebrushes, poinsettias and parakeets 113
Conservation areas 114
Walks and Excursions 116
Literature, References, Acknowledgements 120
Index 121
‘‘Lying at the gate to the tropics, yet only several days‘ journey away from Spain, Tenerife boasts a great deal of the splendour nature has bestowed upon the equatorial landscapes. Its flora already contains several of the most beautiful and largest plant forms. Whoever possesses a sense for natural beauty, will find it an even more powerful tonic on this glorious island than its climate. No place on earth seems to me more suited to banish melancholy and to restore peace upon a pain-wracked mind“.
Thus wrote the famous German naturalist Alexander von Humboldt, when staying on Tenerife in 1799. Despite human intervention, this magic still prevails today. When approaching Tenerife by water or air, one is initially overwhelmed by the dominating presence of the Teide volcano, which in winter is covered in snow. The volcano majestically hovers above everything and gives Tenerife its unique and unforgettable character that sets it apart from all the other Canary Islands. However, the island possesses further, initially less obvious peculiarities. Here, bizarre phenomena of volcanism are closely linked to the unique biology of the island. It is inhabited by animals and plants of strange appearance, which can only be found here. Desert-like habitats, and wet laurel forests of ancient origin await the visitor. Here, life processes, which would normally encompass whole continents and geological time scales, have taken place in very close geographical proximity.
The golden apples of the Hesperides
Eurystheus, king of ancient Mycenae, gave twelve tasks to the legendary Greek hero Heracles; these served as atonement for the murder of his wife and three children committed by Heracles in a moment of mental incapacity. The eleventh task was to steal several golden apples from the Hesperides, the daughters of Atlas, bearer of the heavens. According to legend, the Hesperides, with the help of the hundred-headed dragon Ladon, were guarding a tree carrying golden apples in a beautiful garden located at the western edge of the ancient world. The special importance of these fruits lay in their ability to bestow endless youth upon the gods. Heracles sought out Atlas, and in order to avoid a battle with the dragon, persuaded him to pick the apples for him. In return he offered to carry the heavens. Atlas agreed. However, when he returned with the apples, Heracles asked him to carry the firmament one last time, in order to give himself time to adjust to the weight. The gullible Atlas consented to this – and still carries the heavens to this day.
Scholars of Greek mythology have put forward the attractive hypothesis, that the beautiful gardens of the legendary Hesperides represent the Canary Islands. It is possible, that, seafarers of ancient times returned from their long journeys with fantastic reports of the Canaries. It is thought, that the up to one and a half metre long Tenerife Goliath Lizard, which only became extinct in relatively recent times, served as inspiration for the fantastic creation of the dragon Ladon. And even the golden apples can still be encountered today. Mostly it is thought, that these refer to the fruits of the Canary Strawberry Tree. Although these do not grow as single fruits, but form panicles similar to those of the grape, they look like their name suggests similar to a strawberry. Furthermore, sailors of ancient times should have been familiar with this fruit from their Mediterranean homelands, and thus, it would hardly have made a suitable substance for the creation of a legend. Possibly, the legend could also refer to the three to four centimetres sized fruits of the Canary Bellflower (found on the western Canary Islands), which resemble apples in their shape and colour – glowing golden against the dark of the laurel forest. In contrast to the fruits of the Strawberry Tree, which although they can be eaten raw, are of little flavour, those of the Bellflower are sweet and tasty. They would have been a desirable source of food for humans and the extinct Tenerife Goliath Lizard alike. This could have been another potential source for the legend, which tells of the apples being protected by a dragon.
Alexander von Humboldt: enthusiastic explorer of Tenerife
It was the German explorer Alexander von Humboldt (1769-1859), who, while on his famous expedition to South America in 1799, had a stopover on Tenerife, during which he shifted the island into the focus of the international scientific community. Despite the shortness of his stay, which lasted only one week, von Humboldt accomplished a remarkable scientific feat. During his ascent from the coast to the peak of the Teide, he listed and described the relationship between plant species distribution and altitude. With this work, he created the basis of our current knowledge of the vegetation of the Ca-
naries. He was able to show that the occurrence of particular plant species was primarily determined by the availability of water and the ambient temperature. Both of these factors vary according to altitude, and also depend on whether the north or the south side of the island is concerned. Not least, he realised that the joyfully singing common canaries found distributed across Europe, had originated from the Atlantic Canary, which is found on Tenerife. Furthermore, he discovered and described the beautiful Teide Violet growing at an altitude of 3,510 metres.
Inspired by von Humboldt, a growing number of scientists and naturalists became keen to travel to the Canary Islands. Even the great scientist Charles Darwin (1809-1882) planned to follow in the footsteps of von Humboldt, and explore Tenerife at the beginning of his famous expedition around the world. However, to his great chagrin, this plan was thwarted, when his ship, the Beagle, lay anchored in the port of Santa Cruz de Tenerife. He was prevented from going ashore, because of an outbreak of cholera in England, which led the Spanish port authorities to place a 12-day quarantine on the crews of any vessels travelling from that country. This was taking too long for the captain of the Beagle, and he continued on his journey. Darwin wrote to his father: “We were becalmed for a day between Teneriffe and the Grand Canary, and here I first experienced any enjoyment. The view was glorious. The Peak of Teneriffe was seen amongst the clouds like another world. Our only drawback was the extreme wish of visiting this glorious island.”
Volcanism and geology
The Canary Islands originated through volcanic activity, and they are relatively young in geological terms. The age of the individual islands decreases from east to west. Situated closest to Africa, the oldest island is Fuerteventura, which goes back 21 million years. In contrast, the most westerly islands of El Hierro and La Palma originated only 1.5 and 3 million years ago respectively. Tenerife started emerging from the sea around 11.6 million years ago.
It is interesting to note, that this large island was originally made up of three separate areas of vary-
ing age, the Anaga Mountains to the North East, the Teno Mountains to the North West, and the Roque de Conde in the South West, which only subsequently merged following further eruptions. About 3.5 million years ago, a huge volcanic massif rose between these areas from the sea, in today’s location of the Teide.
It was long thought, that this massif had eventually collapsed into the emptied chamber of magma generated during its formation, and thus created a plain surrounded by mountain ranges, comprising an area known today as the Cañadas. More recent geological research however, shows that the volcanic massif became instable due to its height, and that masses of rock slid down the north side of the island into the sea. This led to the formation of a large rubble chute below sea level, which can still be found today. The top-most part of this side-erosion, forms today’s Cañadas, with the Montaña de las Cañadas as well as the Roques de García representing the only remaining parts of the ancient volcanic massif.
In a third phase, a few thousand years ago, sustained eruptions near the edge of the plain caused the rising of the 3,718 metres tall Pico del Teide and its neighbouring volcano Pico Viejo to the West (which is 3,134 metres tall and the second highest peak of the Canaries). Their lava ran into the Cañadas, and contributed to their formation. Up until recently, volcanic activity has been ongoing on Tenerife, and small eruptions continue to occur. Thus arose the Montaña Blanca at the foot of the Teide 2,000 years ago.The last eruption took place in 1909 on the Chinyero, a 1,556 metres tall cone of slag. Then, ash and glowing lava masses were covering an area of two square kilometres, and only came to a halt close to the village of Santiago del Teide. In 1704 and 1705 lava masses of the Volcán de Garachico destroyed part of the town at its base, including the harbour. Within the Cañadas, the last eruption took place in 1798 at the Narices del Teide, “the nostrils of the Teide”, which are located at the side of the Pico Viejo. Two huge and clearly visible black tongues of lava spilled from them into the Cañadas.
The island of Tenerife has the shape of a pyramid with a triangular footprint. It rises from a depth of 3,500 metres from the sea floor, and reaches an overall height of 7,000 metres. This makes the Teide the third largest volcano on earth. Alongside volcanic activity, the various side-erosions of some volcanoes have much contributed to the formation of the existing landscape. Thus the valley of Icod, the valley of Güímar, the Teno Bajo plain and the Orotavatal were created between 370,000 and 650,000 years ago. An avalanche of rock masses generated by the side-erosions plunged far into the ocean, covering an area of sea floor much larger than the size of Tenerife itself. The landscape is further defined by barrancos, which radiate from the centre of the island to the coast. Barrancos are V-shaped valleys, eroded by water. Due to their young geological age, they are still knife edge-sharp and are characterised by steep walls that cut deep into the rock.
Stone roses, organ pipes and Teide-eggs
Tenerife boasts a large number of volcanic phenomena, and is also an El Dorado for visitors with an interest in geology. The volcanism bestows the landscape with a bizarre character of great aesthetics. It achieves this by lending it shape and colour, such as those caused by the chemical composition, as well as the formation- and cooling-temperatures of the volcanic materials. The lava flowing from active volcanoes cools down and sets on the earth’s surface in variety of forms, depending on the lava’s temperature and gas contents. Thus, thin fluid lava turns into a smooth and easy to walk on surface called Pahoehoe-lava. This Hawaiian expression means “barefoot lava”, as the Hawaiians are able to walk on it on bare feet on their island. If the erupted material is of higher viscosity, it results in the sharp-edged, impassable Aa-lava. Both types of lava occur on Tenerife. Forming a thick layer, the hot lava congeals and hardens into metre-long hexagonal columns, which reach deep into the ground. This is particularly well demonstrated at Los Organos near Aguamansa. Here, thousands of these organpipe-resembling columns build a tall rock wall. A similar process created the form of the Rosa de Piedra, a gigantic basalt rose on the road from La Orotava to the Teide. In this case, lava streams trapped in narrow trenches or barrancos, cooled down evenly on all sides, resulting in a radial pattern of crystallising basalt columns leading away from the centre. Very often it is possible to see metre-wide vertical, or slightly diagonal stone corridors or dykes running through the rock walls, which can structurally be differentiated from the surrounding type of stone. These form, when fissures created during the cooling down process, are re-filled with liquid lava.
If a volcano erupts explosively, unhardened rock materials are ejected into the atmosphere; these are called Tephra. Depending on particle size, they are referred to as ash (when under 2 millimetres in size), or lapilli (when between 2 and 64 millimetres in size). If they are larger than 64 millimetres, they are called bombs or blocks, depending on whether they are round or of angular shape. The impressive Huevos del Teide or Teide-eggs, which can be admired when ascending the Teide, are located at the foot of the Montaña Blanca. They are huge bombs, which are several metres in diameter. Ejected under very high pressure, they rolled down the slope of the Teide, covering various distances. During their journey, they cooled off and hardened, which caused them to obtain their characteristic round shape.
When, during eruption, liquid lava frothes up in the presence of water vapour and cabon dioxide, the result is the formation of pumice. This type of rock is so porous and light, that it is able to float on the water surface. On some of the shores of Tenerife, it is possible to find a broad seam of fine pumice particles, which were broken up and deposited by the surf. A particularly spectacular tuff landscape was formed in the Paisaje Lunar near Vilaflor. Here, erosion has carved the soft stone with a bizarre relief, giving the area the name “moonscape”.
When cooling down rapidly, lava of low water content congeals into a molten mass, containing small regular crystal structures. This mostly shiny, dark-green to black coloured glass is called obsidian, and can be found at many lava streams in the Cañadas.
On rafts,
flying and
as stowaways
The Canaries were formed by volcanic activity, and lie isolated by the sea. Therefore, the plants and animals inhabiting the islands are of particular biological interest. In this context, the most important factors involved are the distance to the nearest continental coast, the species-specific ability of dispersal, as well as pure chance. Thus, there principally exists an invisible filter, which reduces the
ability of successful colonisation to a limited number of species. Naturally, flying species are advantaged within the animal kingdom. To this day, certain species of birds and insects can be found migrating between the continent and the Canary Islands, as well as between islands. Several species of spiders are able to propagate their young through so-called “ballooning”. They drift on the wind, using their ejected threads. Other species arrive on the islands via involuntary rides whilst attached to logs or driftwood. This is probably how the ancestors of today’s lizards, the Geckos and the Skink got to Tenerife. Reptiles are able to survive such journeys, because their extraordinary metabolism allows them to get by without water for extended periods of time. Furthermore, they can tolerate the moisture of salt water on their body surface. In contrast, not a single frog- or caudate-species has survived the crossing, as their thin skin gives very little protection from the salty water of the sea. All amphibians present on the island today, have been introduced by humans. Mammals too, found it difficult to make the crossing, because they are unable to survive long without water. Apart from flying bats, the only mammal species to have reached Tenerife was the ancestor of the now extinct Giant Rat. Not a single exclusively freshwater inhabiting fish species has managed it. Only
the seawater
tolerant Eels, which
migrate from freshwater to
the Sargasso Sea in the West Atlantic to spawn, and are thus tolerant to seawater, can be found in the streams of the barrancos.
Plants with airborne seeds, such as the composite flowers and milkweeds, were carried to the Canaries by the wind. Other plant species arrived as part of flotsam, alongside many of the animals found on Tenerife today. Others yet, could have utilised a very unusual way of transport across: they might have arrived as part of the gastric contents of birds. In the case of several plant species their successful spreading depends on the latter, as their seeds will indeed only germinate after passing through the gut of a bird. It can thus for example be assumed, that the ancestors of the laurel pigeons themselves provided the basis for the formation of the laurel forests, whose fruit feeds their descendants today.
One species results in many – the Galapagos of the Atlantic
Volcanic islands rising from the sea are the laboratories of nature, and offer a time-lapse view of the exciting evolutionary processes leading to the development of new plant and animal species. The colonisation of the Canary Islands by plant and animal species occurred primarily from the neighbouring North Africa and the Iberian Peninsula. However, many of the species originally settling on Tenerife, did not stay the same. Due to the spatial separation from their original form, they have genetically changed so much over time, that they developed into independent sub-species and even species.
Spatial seperation is nevertheless not the only contributing factor in the origination of new species on the Canary Islands. If bad luck hadn’t prevented Darwin from going ashore on Tenerife before reaching the Galapagos
Islands, he would have already been able to make his observations, which later crucially contributed to his formulation of the ground-breaking theory of evolution, here; as comparable processes take place on the Canary Islands. On Galapagos,
he thus discovered the famous Darwin “finches”, as well as the lesser known mockingbirds; the latter of which contributed far more to Darwin’s crucial conclusions. He found, that one single species of mockingbird diverged into four new species. Furthermore, one species of finch diverged into as many as 14 new species, which are characterised by the varying shapes of their beak. For the most part, the latter have evolved in adaptation to a variety of sources of food.
Volcanic activity has time and again caused the formation of isolated oceanic islands, such as the Galapagos or the Hawaiian Islands, but also the Canary Islands. The great distances that separate them from the nearest continent lead to a limitation in the number of species colonising them. The latter results in an initial under-utilisation of many potential habitats, which in turn creates an opportunity for the successful settlers. Plants colonise new sites, and animals tap into new sources of food. Over time they become more and more adapted and specialised.
In this way, one original species evolves into several independent species, which are no longer able to reproduce with each other. This evolutionary process is called adaptive splitting or adaptive radiation. On the Canary Islands, too, new species developed as a result of adaptive splitting. Especially on Tenerife, the development of diversity was facilitated by the enormous gradient in height between sea level and the top of the Teide, as well as the trade winds-related differences between its north and south side. This is the reason why compared to the other Canary Islands, Tenerife boasts the greatest wealth of endemic species. The term endemic refers to species, which exclusively occur at a certain location. As an example, they might be exclusively found on Tenerife or likewise on several of the Canary Islands.
In contrast to the island’s plants, the adaptive splitting is less obvious and spectacular in the local animal species, which is possibly due to their small size and the fact that they live mostly hidden from the observer. Some of the most impressive examples of plants are members of the stonecrop and spurge families, the dill daisies, ironworts, sea-lavenders, cinerarias and last but not least sowthistles, some of which are called “giant Dandelions” because of their appearance and size. The Canary Islands are home to about 6,000 invertebrate species, approximately half of which are endemic: this, for example is the case for 85 snails, 100 spiders, 18 woodlice, 46 millipedes, 50 bugs and 260 beetles. By comparison, “only” just under a third of the 1,000 vascular plants found on the Canaries are endemic.
Colourful viper’s buglosses
A particularly nice example of the evolution of new species via adaptive splitting or adaptive radiation can be found in the various species of viper’s bugloss, which are members of the borage family. On Tenerife, one single original species of this plant has developed into eleven new species, all of which arose through adaptation to their various environments. The “animal” component of this plant’s name derives from the shape of its single flower, from which stamens protrude like vipers’ tongues. The original species was probably similar to Bonnet Viper’s Bugloss, a small blue flowering herbaceous annual plant. By contrast, the rest of the newly developed species are perennial woody plants, colonising a diverse range of habitats and regions. The most impressive of them is the red-flowering Wildpret Viper’s Bugloss, which inhabits the Cañadas and surrounding areas at altitudes between 1,800 and 2,300 metres. This species forms candle-like, up to three metres tall inflorescences, consisting of thousands of flowers closely arranged in double-winding rows. These flowers successively form from the base to the top, which results in prolonging the time window during which they can be pollinated by insects. This is possibly an adaptation to the relatively small number of such insect species on Tenerife. A parallel case is the Simple Viper’s Bugloss, which is of similar size and can be found in the North East of the Anaga Mountains. Because of their thick taproot and short stem, botanists call them collectively rosette trees. They take several years to reach full height and only flower once. After that, the plants die. This group also includes the Auber Viper’s Bugloss, which is characterised by branched and up to one and a half metres tall blue inflorescences. It can be found growing on the loose pumice gravel of the Cañadas.
At exposed sites on lower ground grows the up to two metres tall and strongly branched Green Viper’s Bugloss. It carries cylindrical blossoms at the ends of its many branches. The North East of the Anaga Mountains is home to the Giant Viper’s Bugloss, which grows to about two and a half metres in height. It is multi-branched and forms broad cone-shaped inflorescences with white flowers.
Apart from these viper’s bugloss species, which are endemic to Tenerife, there are a number of other species. Like Bonnet’s Viper’s Bugloss, these can be found on the other islands as well: Prickly Viper’s Bugloss with white flowers and spiky leaves, Upright Viper’s Bugloss, especially on the northern side of the island, and Dull Viper’s Bugloss on dry ground in the South. The only bugloss species introduced by man, the Purple Viper’s Bugloss dominates on fallow grounds and roadsides. It is easily identified by its broad ground-hugging leaves.
A biological window into the past
The colonisation of the Canary Islands by plants and animals began as early as the tertiary period many million years ago. Whilst the cooling down of the climate of the colonisers’ original habitats in the Mediterranean area led to a change of the animal and plant communities there, the Canary Islands maintained a temperate climate due to their oceanic location, which offered an opportunity of survival. The Canary Islands can therefore give insights into earlier geographic patterns of animal and plant distribution, which have been corroborated by fossil records. Probably the most impressive example of this is the laurel forest. It derives from woods, which formed around the Mediterranean 20 million years ago during the tertiary period. Today’s laurel forests are remnants and descendants of an earlier geological age. A visit represents a travel back to times long ago. The formerly merged areas of distribution of other species were separated by the expansion of the Sahara. This period of drying up began about 7 million years ago, and occurred parallel to the previously mentioned climatic cooling. This explains the unusual genetic kinship of some species here with those closely related in far away parts of the world. Thus, the closest relative of the Canary Pine, the Chir Pine, is found in central Himalaya. The Ceropegias are closely related to some species in eastern Africa, and the Barbusano, a species of the laurel tree family, is related to species in India. The Balsam Spurge occurs on the Canaries, in West Africa and in the southern Arabian Peninsula. The two closest related species of the characteristic Canary Bellflower are found in East Africa. Despite the large geographical distance separating them, the Canary Red Admiral is so similar to the Indian Red Admiral, that both butterfly species were originally described as one species. The closest relatives of the butterfly Canary Blue are inhabitants of the far away Mauritius in the Indian Ocean.
Giants and flightless creatures
Apart from the emergence of many new species via adaptive splitting, there are other interesting evolutionary developments taking place on newly formed islands. Thus, the tortoises of Galapagos have evolved into species of gigantic size. Examples of this so called gigantism can also be found on the Canary Islands. The extinction of the over one metre long Tenerife Giant Tortoise pre-dates the first colonisation of Tenerife by humans. Fossil records have shown that this species has been resident on Tenerife since the Miocene period, 20 million years ago, until about 10,000 years ago.
The people who colonised Tenerife were still able to observe the Tenerife Goliath Lizard, which was more than one and a half metres in length. An exact identification of the species was possible from skeletal remains, as well as two mummified specimens of the lizard, which were found in the lava tunnel Cueva del Viento. Another example of gigantism can be found in a rodent, the Tenerife Giant Rat, whose body measured over 40 centimetres in length (not including the tail), and weighed more than a kilogram. Its remains, too, were found in lava tunnels. The Giant Rat was evidently capable of climbing trees in order to forage for food. Archaeological finds have confirmed that both species, the rat as well as the lizard, had been used as a source of food by the original human inhabitats. This has been deduced from abrasions and injuries of bones found. Thus, both species became extinct in relatively recent times. Other remains of these extinct animals can be studied to this day at the Museo de la Naturaleza y el Hombre (the Museum of Nature and Man) in Santa Cruz.
Birds, whose wings have regressed so much that they are no longer able to fly, can be found on nearly all continents, and especially on small oceanic islands. Several examples of this can also be found on Tenerife. The small, approximately sparrow-sized flightless Long-legged Bunting had adapted to a life entirely spent on the ground. Its wings were shortened by about a third, and its legs elongated. The crest of the breast bone, where a bird’s wing muscles attach, had regressed to a large extent. However, its bones by contrast, weighed at least a third more than those of related species. There probably used to be another kind of flightless bird on Tenerife, the Canary Quail. It was first discovered at archaeological digs on the neighbouring island of La Gomera, and pointed towards the species being hunted by humans. Possibly both of these bird species became extinct by falling victim to introduced rats, as well as domestic cats, which were brought early on by the natives of the islands. It is unknown what caused the extinction of the predominantly ground-dwelling Slender-billed Greenfinch, which was only discovered in 2010 in the Cueva del Viento.
The Habitats
Climate and biology
The Canary Islands are characterised by an even climate. This is primarily due to the Canary Current, a cool to moderate ocean current in the North East Atlantic. Apart from an occasional short-lived deterioration of the climate, influenced by the North Atlantic or the Sahara, life on the Canaries is predominantly affected by the more or less strong northeasterly trade wind. The latter is created by equatorial air masses of higher temperatures, which during their ascent of up to 3,000 metres cool down and form the so called anti-trade winds, flowing in the directions of the North and South Poles. When they reach about 30 degrees latitude, they begin to sink, and revert back and flow into the direction of the equator. During this process, the air of the lower strata close to the ocean becomes gradually cooler, which results in an uptake of moisture from the Atlantic. Above approximately 1,500 metres however, the air remains warm and dry. The earth’s rotational forces cause masses of air streaming down from the North to spin to the West. This results in the northeast trade winds, which played a huge role during the age of sailing ships. They carried the ships of explorers such as Christopher Columbus and naturalists like Alexander von Humboldt via Tenerife to America.
Of even greater importance is the influence of the trade winds on the flora and fauna of Tenerife. When these encounter the wall-like north side of the island, air masses are driven up, resulting in the condensation of the moisture previously absorbed from the Atlantic. This causes the formation of a continuous cloud at an altitude between 600 and 1,500 metres, which is confined by a warmer, drier stratum. This cloud cover is more extensive in winter than in summer, and can be admired as a sea of clouds from the heights of the Cañadas. Due to offshore winds it dissolves again at night. By contrast, the south side of the island stays free of trade wind clouds. An interesting situation can be observed in the Anaga and Teno Mountains, neither of which are high enough to completely dam the northeasterly trade winds. From their ridge roads and passes, it is possible to see wispy clouds getting whipped across the crests at higher altitude, only to dissolve again completely within seconds upon reaching the warmer south side.
The variation in the distribution of moisture and sunlight leads to a vertical striation of the vegetation into various plant communities of remarkable structural organisation. Due to variation in the prevailing climatic conditions, the limits of this zonation on the north side can differ considerably in height from that of the south side. This change in plant communities can be observed when travelling up to the Cañadas to the top of the Teide, coming from the seaside resorts in the South, or on von Humboldt’s trail from Puerto de la Cruz from the north coast. Because of the height of the Teide, the zonation on Tenerife is far more pronounced than on the other Canary Islands, and it is the main reason for the island’s species richness. In coastal areas, the salt content of the wind driven air benefits plants, which are able to tolerate high salinities. Here, and in the adjacent dry zone, grows the Succulent shrub. This area encompasses the dunes of El Médano. Here, plants thrive, which have adapted in various ways to a lack in moisture. An overlapping zone is the Thermophilic forest. However, due to a transformation of this zone into agricultural land, the latter can now only be found on a small scale. Influenced by the trade wind cloud, Laurel forest and Myrtle and Heath forest can be found on the north side, but, are generally absent from the south side, due to the drier conditions found there. The next vegitational zone is the Canary Pine forest. Areas of high altitude, such as the Cañadas, are home to the tree-less Teide Broom scrub. The highest zone is dominated by the alpine flora of the Teide Violet zone.
El Médano: Rocky shores, beaches and sand dunes
The only sand dune habitats on Tenerife are found near the town of El Médano in the South West of the island. Together with the volcano Montaña Roja these form a nature reserve, the Reserva Natural Especial Montaña Roja. In contrast to the predominantly steep cliffs found on the island, the sea here is very shallow, which allows sand to get washed up on the shore. The sand consists of millions of calcareous fragments of mollusc shells and the exoskeletons of crabs, which were smashed up by the breakers and surf of the sea. Over time, this has resulted in the formation of a wide beach here. The wind carries the sand further inland, where it is trapped by shrubs, such as Balancón, and collected into continuously growing dunes. These have given the area its name. Whereas the dune sand trapped by plants is largely in motion, salty sea spray and the heat of the sun, have baked the sand at the foot of the Montaña Roja into a fossilised dune. Close to the shore, the wind has exposed low, rock-solid circular cones, and elongated ridges of encrusted sand. These follow the original routes of plant roots, whose secretions (root exudates) led to a solidification of the surrounding sand.
El Médano is primarily home to sand-dwelling plants which are tolerant to salt, such as Sea Spurge, Capitate Seaheath, Canary Samphire, Uva de Mar, as well as Sericeous Schizogyne. Here also resides the unique Canary Sand Carrot, which can only be found at one other location on Tenerife.
During spring, peculiar, and initially confusing ringing sounds are heard everywhere. These are made by the males of the Red-winged Grasshoppers, which due to their camouflage are very difficult to spot. As part of their bizarre mating ritual, they can be seen briefly ascending to a height of about one metre, whilst generating a whirring sound with their wings. Upon landing, they proceed to perform their characteristic song, which is reminiscent of the low trilling of a whistle.
Life in the surf zone
Considering the steep rocky cliffs of Tenerife, which are continuously battered by the power of the incoming breakers, it is difficult to imagine that some animals have been able to adapt to even such harsh conditions. The latter are best observed at low tide, when the hard black surfaces of rock and the loose rounded volcanic stones and boulders have fallen dry and are lying exposed. Then, the only remaining water is found in rock pools. Now it is possible to make out a small light-coloured seam of star-shaped bumps covering the dark rocks. These so called Poli’s Stellate Barnacles are small crabs, which are permanently attached to the substratum, and are thus able to survive the force of the waves. Their legs are shaped into a filter-feeding apparatus, which enables them to extract food from the churned up water at high tide. At low tide, they protect themselves from drying out by covering mouth and extremities with their exoskeleton. With its many long legs, the Marbled Rock Crab can be quite scary in appearance. They are master climbers, and specimens of varying size can be found in great abundance on the steepest rock walls above the tide line. They are mostly dark, but can occasionally be bright yellow
and red in
colour. They
need to return to the wet
element regularly, in order
to keep their gills moist enough
for respiration. This is also where their larval development takes place. The crabs feed on marine plants and animals, which have been crushed by the waves. In order to grow, the crabs have to shed their old “skin” repeatedly. Their empty hard exoskeletal molts can therefore be found in large numbers, and are easily mistaken for living crabs. Only on close inspection does it become apparent, that the molted crab has grabbed onto a crevice in the rock, and all that is left is its empty shell.
Gastropods are also well adapted to life in the surf zone. They are able to firmly attach themselves to the substratum, and have sturdy shells. Rocky crevices and small pockets of seawater are home to dense groups of periwinkles and thick topshells. Periwinkles posses a lung-like organ, which has replaced the gills, and ensures the snails’ survival during low tide. Limpets have adapted especially to life in the intertidal zone. With their shell resembling a shallow bowl, they are externally almost unrecognisable as members of the gastropod class. They produce and secrete an acid, which enables them to partially dissolve the rock around the edge of their shells. This allows them to closely adapt their fit to the substratum. However, the animal leaves this seat in order to forage for food. All of these snails are herbivores, using their rough “tongues” to grate encrusting algae from the rocks. Thick topshells, burgados, as well as limpets, lapas, have traditionally been harvested by the natives, and are still collected and eaten today.
Explorers of the coastal zone will notice how again and again individual snails detach themseleves from the rocks and drop. After an initial period of lying motionless where they fell, they eventually hurry away at remarkable speed for such animals. The puzzle is easily solved. On further investigation it becomes apparent that they are in possession of legs: they are in fact Hermit crabs, which permanently inhabit the shelter of empty snail shells. As they grow, they are forced to look for increasingly larger homes.
The rock pools, too, are full of life. Large numbers of elongated appendages shimmering in magnificent green and violet can be seen protruding from crevices in the rock. They only come to life when touched. It is not immediately obvious whether one is dealing with a plant or an animal, although its behaviours points towards the latter. It is the Snakelocks Anemone, an anthozoan, which is characterised by a multitude of tentacles. It owes its beautiful colouration to its symbiotic coexistence with small single-celled algae. These so-called zooxanthellae, which find shelter inside their host, provide the Snakelocks Anemone in return with nutrients, such as sugars and starch. The anemone’s tentacles are armed with poisonous nettle cells, which are used to catch small fish and crabs.
Other animals are quick to take cover when a shadow is cast across their rock pool. These include the almost transparent Rockpool Shrimp, as well as two small, up to 15 centimetres long fish species, the Rockpool Blenny and the Madeira Goby. Both are able to withstand strong waves, and attach themselves to the ground or crevices in the rocks with the aid of their fins and bodies.
Most animals carried in on the tide are smashed up completely on the rocky volcanic coastline. Only on shallow beaches, the shells of various bivalves and Common Cuttlefish survive. Very rarely the blue-tinted bladder-like floats of the Portuguese Man o’ War, an oceanic surface-dwelling siphonophore, can be found here. It consists of a colony of many individual animals, and uses the poisonous nettle cells of its metre-long tentacles to prey upon small fish.
Succulent shrub – “cacti”, ceropegias and plants which can hold their breath
The ecological communities of the coastal and lower regions of Tenerife are primarily characterised by a lack of water. This is clearly reflected in the patchy occurrence of weeds and shrubs, but especially in the striking lack of trees. The plants living here have developed a variety of adaptations to this lack of moisture. Almost all of the species here are able to store water in their tissues during periods of rain, and are called succulents after the Latin succulentus, meaning “juicy” or “rich in sap”. Such tissues can be found either in the leaves or the stem of a plant. Thus, for example, the shoots of the Canary Spurge can be as thick as an arm. It looks so much like the American candelabra cacti, that it often gets mistakenly assigned to the family of Cactaceae, which are exclusive to America. Thickened shoots can also be found in the Verode, which is a composite flower. After it flowers in spring, its parachute-like seeds are dispersed by the wind; very much like those of our native Dandelion.
The deep and wide-reaching roots of the Hanging Plocama collect moisture, and for example, explain, why this plant can still be of a deep green colour even in the driest locations. Water evaporation via a plant’s surface can be reduced in various ways. Examples are the dense silvery hairs of plants like Sericeous Schizogyne, the Dusty Spurge Olive, or the waxy layer of the Ceropegias. Often there is reduction in plant surface, such as the thread-like narrowing of leaves, which fall off during dry periods. In other plants, there is a complete lack of leaves, as in the endemic Ceropegias, whose shoots rise side by side from the ground like thick sticks.
Another particularly interesting adaptation has evolved in many plants of the dry zone: they are able to “hold their breath”. Whilst normally the absorption of carbon dioxide by the open stomata of the leaves and photosynthesis happen simultaneously during daylight hours, these two processes happen at different times in these highly adapted plants. Their stomata are open during night-time only, and the absorbed carbondioxide is chemically bound and stored as malic acid inside the cell vacuoles. During daytime, the stomata are closed, and water evaporation is kept to a minimum. Nevertheless, the plants are able to utilise the sunlight to build organic components, as the “breathed in”, temporarily fixed carbon dioxide is released again and metabolised.
With increasing proximity to the coast, the inland-bound drifting of sea salt plays an important role, as it contributes additionally to the dry climate which adversely affects the distribution of plants. It does this either directly, or via the salinification of the soil. This region is home to the Crystal Reichardia, an endemic species of Tenerife and Gran Canaria, as well as the widespread Canary Samphire. The landscape-defining Balsam Spurge is a salt tolerant plant, too. Other characteristic plants here are the endemic Comb-shaped Sea-Lavender and the Red-stemmed Squill.
