| Laurisilva of Macaronesia * | |
|---|---|
Madeira's Laurisilva forest. |
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| Country | Portugal |
| Type | Natural |
| Criteria | ix, x |
| Reference | 934 |
| Region ** | Europe and North America |
| Inscription history | |
| Inscription | 1999 (23rd Session) |
| * Name as inscribed on World Heritage List ** Region as classified by UNESCO |
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Laurisilva or laurissilva ("laurel forest") is a subtropical forest, found in areas with high humidity and relatively stable and mild temperatures. They are characterised by evergreen, glossy-leaved tree species that look alike with leaves of lauroide type. The members of the Laurel family (Lauraceae) could be prominent, or in association.
Of particular note is the endemic type of humid subtropical laurel forest, macaronesian laurisilva, found on several of the Macaronesian islands of the North Atlantic and Macaronesian African mainland enclaves, namely Madeira Islands, the Azores, Cape Verde Islands and the Canary Islands, a relict of the Pliocene subtropical forests, supporting numerous endemic species.
In Spanish, the word "laurisilva" is used for every laurel forest: Laurisilva misionera, laurisilva valdiviana, etc.
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The laurisilva forests are found in the islands of Macaronesia in the eastern Atlantic, in particular the Azores, Madeira Islands, and western Canary Islands, from 400 m to 1200 m elevation. Trees of the genera Apollonias (Lauraceae), Ocotea (Lauraceae), Persea (Lauraceae), Clethra (Clethraceae), Dracaena (Ruscaceae), and Picconia (Oleaceae) are characteristic.[1] The Madeira Islands laurel forest was designated a World Heritage Site by UNESCO in 1999.
The forests are made up of laurel-leaved evergreen hardwood trees, reaching up to 40 m in height. Many of the species are endemic to the islands, and harbour a rich biota of understorey plants, invertebrates, and birds and bats.
Laurisilva formerly covered much of the mountain areas of Annobon, Azores, Bioko, Cape Verde, Canary Islands, Madeira, São Tomé, Príncipe, other Atlantic islands, and locally on favourable wet climate microenvironments of the coast and coastal mountains of the north-west African mainland, but the forests have been much reduced in extent by logging, clearance for agriculture and grazing, and the invasion of exotic species. The most extensive laurisilva forests remain on Madeira, where they are found between 300 m and 1400 m altitude on the northern slope, and 700 m to 1600 m on the southern slope, and cover 149,5 km². In the Canary Islands, roughly 60 km² of laurisilva remain on Tenerife, smaller areas on La Palma, over 20 km² in Garajonay National Park on La Gomera, and relict areas in Gran Canaria. In the Azores, small patches of laurisilva forest remain on the islands of Pico, Terceira, and São Miguel.
The Madeira laurisilva forests, the largest remaining stands, were declared a UNESCO World Heritage Site in 1999.[2] Predominant lauraceous trees include Til (Ocotea foetens), Loureiro (Laurus novocanariensis), Vinhático (Persea indica), a valuable hardwood, and Barbosano (Apollonias barbujana); other important trees include Aderno (Heberdenia excelsa), Pau Branco (Picconia excelsa), the Mocanos (Visnea mocanera and Pittosporum coriaceum), and Sanguinho (Rhamnus glandulosa), and the small trees or large shrubs Folhado (Clethra arborea) and Perado (Ilex perado). The forests support a diverse understorey of ferns and bryophytes,[3] which both require moisture for reproduction, evergreen climbing plants like Canarina canariensis, asparagus species and Araliaceaes (Hedera helix, Hedera canariensis) and of herbaceous plants, including the Leitugas (Sonchus spp.), geraniums (Geranium maderense, G. palmatum and G. rubescens), the Estreleiras (Argyranthemum spp.) and the endemic orchid Goodyera macrophylla.
Lanzarote and Fuerteventura are very close to the African mainland (96 km), and were even closer during the Ice Age of the Quaternary (18,000 years ago, roughly 60 km). The vegetation is very similar to the basement floor of the eastern Canary Islands. A large number of plant species and some animals are common, mainly arthropods, but the most unusual given that many of these taxon are endemic to both regions, the insular and continental. Often displayed species vicarious within a gender which, in turn, is endemic in both regions:[4] Lotus marocanus / Lotus glaucus; Bubonium intrincatum / Bubonium sericeum; Euphorbia echinus y Euphorbia beaumieriana / Euphorbia handiensis; Kleinia anteuphorbium / Kleinia neriifolia; Lavandula maroccana / Lavandula multifida; Sonchus leptocephalus / Warionia saharae.
The phytosociology of these configurations was described in a paper by Rivas Goday and Esteve Chueca.[5]
A large relict population of the drago plant (Dracaena) was recently discovered in some of the Macaronesian islands, together with associated vegetation, including trees.
The Euphorbia species tabaiba and Euphorbia cactus are marker species defining the concept of the Macaronesian ecotype..[4]
The decline of much of the endemic laurisilva fauna and flora is largely due to deforestation to accommodate agricultural expansion. This is accompanied by displacement of native flora by invasive alien weeds and crop plants.
Most of the mammalian species in the laurisilva are bats, but two species of giant rats existed on the islands of Tenerife and Gran Canaria; they survived until shortly after human settlements were established on the islands. These giant rats of genus Canariomys[6] attained a weight of about 1 kg.
The kinglet of Madeira is known as the Madeira firecrest, Regulus madeirensis [7] Until recently, it was considered to be a subspecies, R. i. madeirensis, of the Common Firecrest R. ignicapillus. However, phylogenetic analysis based on the cytochrome b gene showed that the Madeiran form is a distinct species.
The Azores Bullfinch Is threatened and if it is to recover, the ecology of the northern archipelago of Macaronesia must be effectively restored. Projects attempting to re-establish the original laurel forest habitat in the eastern monteverde of São Miguel are under way.
Some species of pigeons are endemic to Macaronesia; Bolle's Pigeon, the Laurel Pigeon and Trocaz Pigeon, are thought to be derived from island populations of the Columba palumbus.[8] Other non-endemic species such as the Afep Pigeon also occur on the island.
The Atlantic archipelagos of the Canaries, Azores, and Madeira have a volcanic origin and they have never been part of a continent. The formation of Madeira started in the Miocene and the island was substantially complete by 700,000 years ago.[9] At various times in the past, the major islands of these archipelagos were all colonised by ancestral wood pigeons, which evolved on their respective islands in isolation from the mainland populations. In Azores Islands, of extinct species laurel forest mountain pigeon or Azores black pigeon (Portuguese: pombo da serra). Mitochondrial and nuclear DNA sequences suggest that the ancestor of Bolle's Pigeon may have arrived in the Canaries about 5 mya, but an older lineage that gave rise to another Canarian endemic, the Laurel Pigeon, C. junoniae, may date from 20 mya.[10] The most recent wood pigeon arrival on Madeira was that which gave rise to the subspecies C. palumbus maderensis and Azores Wood Pigeon C. palumbus azorensis.
The Trocaz Pigeon was formally described in 1829 by Karl Heineken, a German medical doctor and ornithologist who was living on Madeira at the time. He recognised it as different from the now-extinct local form of the Common Wood Pigeon, which he called the "Palumbus", and noted that the two pigeons never interbred or habitually associated together. He suggested designating the new species by its local name, "trocaz".[11] Trocaz is a variant of Portuguese torcaz, the Common Wood Pigeon; both words are ultimately derived from the Latin torquis, a collar, and refer to the bird's coloured neck patches.[12] This is a monotypic species, although in the past Bolle's Pigeon was sometimes regarded as a subspecies of the Trocaz Pigeon.[13]
The laurisilva forests of Macaronesia are relicts of a vegetation type which originally covered much of the Mediterranean Basin when the climate of the region was more humid. With the drying of the Mediterranean Basin during the Pliocene, the laurel forests gradually retreated, replaced by more drought-tolerant sclerophyll plant communities. Most of the last remaining laurisilva forests around the Mediterranean are believed to have disappeared approximately 10,000 years ago at the end of the Pleistocene, when the Mediterranean basin became drier and with a harsher climate, although some remnants of the laurel forest flora still persist in the mountains of southern Spain, north-center of Portugal and northern Morocco, and two constituent species (Laurus nobilis and Ilex aquifolium) remain widespread. The location of the Macaronesian Islands in the North Atlantic Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate which has allowed these forests to persist to the present day.
Over millions of years, these vegetation covered much of the tropics of Earth. From a biogeographic point of view, the tropics may extend beyond parallels of Cancer and Capricorn; e.g. the peninsula of Florida in the United States lies in the subtropics (latitude greater than 23° 26' N), but hosts many species characteristic of the New World tropics.
One example is the translation of the Tertiary Atlantic laurisilva to its current location. Many plants of the Macaronesian laurisilva have their closest relatives in geographically remote places like South Africa or South America, the genera Persea, Ocotea, and Maytenus, for example, also appear in South American temperate evergreen, which testifies the ancient origin of these flora. Another interesting finding is the presence in various areas of the Mediterranean and the Caucasus up to the Himalayas of plant fossils around 20 million years old, from the Tertiary, very similar or identical to those currently living in Macaronesia.
This type of forest extended during the Cenozoic or Tertiary Era, more than 20 million years, over a wide area of the basin of the Mediterranean, Eurasia and north-west Africa where the climate the region were wetter. At that time there was a Tethys Sea that separated the ancient continents of Laurasia and Gondwana; this sea was much more open than the Mediterranean and ocean currents flowed in a different way, bringing tempering moisture and clima, in areas that currently do not have any influence. Subsequently, the Ice Age which took place at the end of that period and for much of the Quaternary forced the laurel forests to move to warmer southern regions, where conditions were more conducive to their survival, settling in this way on the northwest coast of Africa and in the Macaronesian archipelagos.
During the Quaternary glaciations and expansion of the polar ice caps, resulting in widespread cooling of the climate, the flora of central and southern Europe retreated to more southerly latitudes in search of milder conditions. Also the sea level was lower, with lands today submerged forming land bridges.
The end of glaciations coincided with the spread of deserts in North Africa, notably the Sahara, so this type of forest was reduced to those areas, which act as boundaries between temperate and tropical. At that time, the climate of southern Europe was warmer and wetter than today, and the vegetation that surrounded the ancient shores of the Mediterranean Sea was likely similar to that of the current Macaronesian laurisilva.
The laurel forests of Macaronesia are relics of the vegetation that originally covered the land from the Atlantic to the Caspian Sea before the Ice Age. With the largest periodic drought in the Mediterranean climate due to climatic changes due to changes in ocean currents and continental drift during the Pliocene, laurel forests gradually disappeared, replaced by plant communities of more drought tolerant sclerophyllous flora. Most of the last remaining temperate evergreen forests around the Mediterranean are believed to have disappeared about 10,000 years ago at the end of the Pleistocene, when the Mediterranean basin became warmer and drier, although some remnants of the laurel forest flora still persist in the southern mountains in Spain, north-central Portugal and northern Morocco, and three constituent species, Laurus nobilis, Ilex aquifolium, and Hedera helix, are still widespread. A remarkable adaptation is the asparagus, which in the Canary Islands is preserved in the original form, a leafy vine, while in the rest of the Mediterranean has evolved into a thorny species. The location of the Macaronesian Islands in the North Atlantic Ocean moderated these climatic fluctuations, and maintained the relatively humid and mild climate that has allowed these cloud forests to persist until today.
Many of the then existing species became extinct because they could not cross the barriers posed by the Alpine Mountains and the Mediterranean, but others found refuge as a species relict in coastal enclaves and in the Macaronesian archipelagos, sufficiently far from the ice while protected by the oceanic influence of drying that caused the Sahara. In other parts of the world, including China, Africa or South America, the arrangement of ridges and mountain ranges extending in the direction from north to south, rather than serve as a barrier, permitted the plants' migration to more suitable areas, where they are survive to this day.
With the general warming of the atmosphere and the consequent withdrawal of the ice, flora tertiary survivors could not regain their range in southern Europe, as the new post-glacial climate was drier than that of the Tertiary, and to these new environmental requirements, the primitive tropical European flora evolved and gave rise to the present flora of the Mediterranean sclerophyll. Thus, the Mediterranean flora and fauna have a common origin.
At the same time, isolated from the mainland, the tertiary Macaronesian flora evolved independently, which has led to numerous endemic species. In fact, it should be noted that 50-55% of vascular plant species present in the Canary Islands are unique, and this proportion increases in more distant islands like Cape Verde, Azores and Madeira. Macaronesian laurel forest consists of about 25 tree species, 35 if the species that survive in nearby areas of Eurasia are added, while in the "laurisilva misionera" there are in total over 100 tree species; it is likely that the Atlantic laurel rainforest from the Tertiary had roughly this same number of species of "laurisilva misionera".
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