Location and General Description
This ecoregion covers the three main islands, Réunion, Mauritius, and Rodrigues, and a number of smaller islets of the Mascarene Islands. The largest islands are the French Dependent Territory of Réunion (2,500 km2), and the island of Mauritius (1,900 km2), which together with Rodrigues (110 km2) forms the single independent nation of Mauritius. The nearest landmass is Madagascar, 680 km northwest of Réunion.
Temperatures along the coast are warm and seasonal, in summer (December-April) averaging 30° C, while in winter (May-November) the average is closer to 25° C. At higher elevations and mountain peaks the temperature is cooler, averaging 18° C. Here, snow is not uncommon, though short-lived. The prevailing winds are the southeasterly trades, which blow throughout the year. In the lowlands of Mauritius, the rainfall varies from 890 mm on the leeward side of the island, to 1905 mm on the southeast coast. In the uplands, the rainfall varies from 2540 mm to 4445 mm per annum. The rainfall is sufficient to permit the development of tropical moist forest on the windward side of the island and tropical dry forest on the leeward side. Cyclones also occur, and have helped to shape both the topography and species assemblages on the island. On Mauritius, abundant and heavy rains from these storms have created pronounced erosion, while extremely high winds are thought to be responsible for the apparent lack of large-winged insects (Henkel and Schmidt 2000). Cyclones and accompanying torrential rain cause also significant destruction through landslides.
The islands of Réunion and Mauritius are strongly influenced by their volcanic nature and rugged topographical features, including ravines and cliffs, although Mauritius is significantly older than Réunion. Soils are predominantly laterites in various stages of formation depending on the age of the volcanic parent material. Some volcanic activity is recent, and soils are still forming from the numerous lava beds and fields. Piton de la Fournaise on Réunion (2,525 m) is active several times each year. Topography is steep and rugged on Réunion due to its recent volcanic activity with Piton des Neiges reaching to 3,069 m. In contrast, Mauritius is a very old island, with some geological formations dating back 700 million years. Here, the highest point is Piton de la Rivière, which has long since been extinct and reaches a height of only 828 m. Only the island of Rodrigues has lower relief, rising to 390 m over mainly gentle hills. Many smaller islands also occur in this area; of particular interest in Round Island, a small island off the northern tip of Mauritius with an unusual reptile fauna.
The vegetation of the islands was originally quite diverse, ranging from coastal wetlands and swamp forests, through lowland dry forest, rain forest, and palm savanna to montane deciduous forests and finally (on Réunion) to heathland vegetation types on the highest mountains. Most of the original vegetation is now destroyed. Moreover, almost all remaining native plant communities are badly degraded by introduced species (WWF and IUCN 1994). Major plant families include Sapotaceae, Ebenaceae, Rubiaceae, Myrtaceae, Clusiaceae, Lauraceae, Burseraceae, Euphorbiaceae, Sterculiaceae, Pittoscoraceae, and Celastracea. On Réunion much of the island has been reforested and now contains almost 40 percent forest cover (Henkel and Schmidt 2000).
The flora is diverse and contains many unique species. There are approximately 955 species of flowering plants on these islands in 108 different families and 323 genera. Thirty-eight of the plant genera are considered endemic, and there are approximately 695 endemic species (WWF and IUCN 1994). Most of the flora has affinities with Africa and Madagascar; however, a small percentage is more closely related to that of Asia. Of particular interest is the high diversity of palm species, including many endemic genera.
Of the 16 endemic birds found on these islands, seven are confined to Mauritius, four to Réunion, and two, the Rodgrigues warbler (Acrocephalus rodericanus, EN) and the Rodrigues fody (Foudia flavicans VU), to Rodrigues Island (Stattersfield et al. 1998). The bird species confined to Réunion are the Réunion cuckoo-shrike (Coracina newtoni, EN), Réunion stonechat (Saxicola tectes), Réunion olive white-eye (Zosterops olivaceus), and Réunion bulbul (Hypsipetes borbonicus). The birds confined to Mauritius are: Mauritius cuckoo-shrike (Coracina typical, VU), Mauritius kestrel (Falco punctatus, VU), Mauritius fody (Foudia rubra, CR), Mauritius bulbul (Hypsipetes olivaceus, VU), Mauritius parakeet (Psittacula eques, CR), Mauritius olive white-eye (Zosterops chloronothus), and pink pigeon (Columba mayeri, EN). Three Mascarene endemic birds occur on more than one island, the Mascarene paradise-flycatcher (Terpsiphone bourbonnensis), Mascarene grey white-eye (Zosterops borbonicus), and Mascarene swiftlet (Collocalia francica). Patterns of bird diversity and endemism here are similar to those on Pacific Islands, except that elevation is more important in explaining variations in endemism here than elsewhere (Sinclair and Langrand 1998, Adler 1994). The endemic species are principally confined to the remaining forest patches, although some have started to colonize plantations (Barre 1988, Louette 1988). There are also some rare seabirds breeding on these islands, some of which are believed to be endemic races. Fossil records indicate that before the arrival of early European explorers there were many other bird species present that have since gone extinct (Mourer-Chauviré et al. 1999). Among these are a night heron, an ibis, a teal, parrots, pigeons, and a falcon.
Among the extant mammals the only true endemic is the greater Mascarene flying fox (Pteropus niger, VU). This species is now severely endangered due to deforestation, hunting, introduced species, and cyclones. Another similar species of bat, the lesser Mascarene flying fox (Pteropus subniger, EX), is already extinct. Another rare mammal on these islands is the rare Rodrigues flying fox (Pteropus rodricensis, CR).
There are 13 strictly endemic reptiles on these isl;ands, with large number from the day-gecko genus, Phelsuma (Henkel and Schmidt 2000). Round Island, a small island off the northern tip of Mauritius, is classified as a nature reserve because of the number of rare reptiles that are endemic to the island. These include the Round Island keel-scaled boa (Casarea dussumieri), Round Island skink (Leiolopisma telfairii), Round Island day gecko (Phelsuma guentheri), and the recently extinct Round Island burrowing boa (Bolyeria multocarinata). Other notable reptiles include the radiated tortoise (G. radiata), and the Serpent Island gecko (Nactus serpensinsula). Critically endangered hawksbill turtles (Eretmochelys imbricata) nest on these islands (Hilton-Taylor 2000). There are no endemic amphibians. Although the invertebrates remain poorly known, there are known to be numerous endemic species. As examples, there is an endemic nemertine worm (Geonenertes rodericana) in the damp woods of Rodrigues, and a swallowtail butterfly (Pailio manlius) is endemic to the Black River Gorge on Mauritius. There are also many endemic landsnails on Mauritius, 30 percent of which have gone extinct and another 30 percent which are severely endangered due to the introduction of the competitive and invasive carnivorous snail (Euglandina rosea).
While the Mascarenes still support many endemic species, they are as well known for the large number of species that have become extinct since 1600. These extinctions include the dodo (Raphus cucullatus) of Mauritius, Rodrigues solitaire (Pezophaps solitaria), Rodgrigues parakeet (Psittacula excul), Mascarene parrot (Mascarinus mascarinus), Réunion starling (Fregilupus varius), and the Mauritius blue-pigeon (Alectroenas nitidissima) (Stattersfield et al. 1998). There have also been a number of extinctions of endemic plants, possibly totaling as many as 100 species (WWF and IUCN 1994). The remaining 500-600 endemic plant species are threatened from the considerable loss of habitat and invasion by more vigorous introduced species. Some of these are reduced to handfuls of individuals, or even a single remaining plant. Examples of plant species on the verge of extinction include: Drypetes caustica, Tetrataxis salicifolia, and Xanthophyllum paniculatun.
Mauritius has one of the highest human population densities in the world, 634 persons/km2 (CIA 2000). On all of the Mascarene Islands, there has been a vast loss of the original forest habitat (Stuart et al. 1990). On Réunion, it is estimated that less than 40 percent of the island is covered with natural vegetation; on Mauritius, only about 5 percent of the natural vegetation survives; and on Rodrigues, the natural vegetation covers around 1 percent of the total land area. Different agents have caused this loss of habitat. On Réunion, forest and other habitat is cleared for agriculture and degraded through the introduction of alien plants. On Mauritius, sugar cane, tea, and conifer plantations have replaced the natural vegetation. On Rodrigues, the effects of feral animals and shifting cultivation have changed the forest habitats to a savanna with scattered trees, and introduced plants have then taken over the remaining habitats.
The natural habitats of these islands are heavily fragmented due to the anthropogenic activities that have continued since the 17th century. On Réunion, most of the remaining larger habitat blocks are found at higher elevations. In the lowlands, forest habitat is largely restricted to the steep banks of rivers. On Mauritius, most of the remaining habitats are found in the southwest, around the Black River Gorge (WCMC 1993). Even here the habitats are under great threat. On Rodrigues, the remaining habitat is restricted to small patches on the tops of hills, and in steep riversides. There are some reserves, which also provide places for native habitat and species, but introduced species are a major problem. Rodrigues probably has some of the most fragmented habitats and species distributions of anywhere in the world.
The habitats of the ecoregion are greatly under-protected, even though little habitat remains. There are several protected areas on Réunion, but only three are greater than 10 km2, Mazerin, Bébour and Fôrét des Hauts de St Phillipe State Biological Reserves. On Mauritius, there are several protected areas. The largest is the Black River National Park (66 km2), which is under the process of enlargement. Some offshore islets are also reserved for conservation. There are a number of fishing reserves, but these have not been considered here. On Rodrigues there are only three protected areas (comprising only 0.58 km2), which include the only surviving remnants of natural vegetation. Two of these are small islands and one is located on the mainland. Some other areas have also been fenced to allow regeneration of the natural habitat.
Types and Severity of Threats
The habitats and species endemic to the Mascarene Islands are all under some level of threat. The threats to native vegetation and plant species on these islands are numerous and have been summarized in WWF and IUCN (1994). Some species are critically endangered (e.g. a few plant species are reduced to one individual). Introduced animals are especially problematic. Introduced grazers and herbivores, such as deer, pigs, crab-eating macaques (Macaca fascicularis) (the last is not on Réunion), and even giant snails (Achantina spp.) lead to the destruction of habitat and endemic plant species. Introduced rats, cats, and mongooses (although the last is not on Réunion) prey on adult and young endemic animals, and introduced birds prey on endemic birds.
In addition to the threats from introduced animals, lowland habitats and endemic plant species are destroyed for agricultural conversion, and alien plants invade native habitats. Fruit bats and sea turtles are hunted and directly exploited. Finally, the small populations of many endemic species make them vulnerable to cyclones and other catastrophic events.
Justification of Ecoregion Delineation
The Mascarene Islands are composed of three main islands: Réunion, Mauritius, and Rodrigues, and some islets. Although each island contains distinct flora and fauna, they were included in a single ecoregion due to their possession of some shared endemic species, their similar volcanic history and geophysical characteristics, and their wide separation by sea from other land masses.
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Prepared by: Jan Schipper
Reviewed by: In progress