Flora of Madagascar

Grandidier's baobab is one of Madagascar's six endemic baobab species, icons of the island.

The flora of Madagascar is part of the island's unique wildlife. Madagascar has more than 10,000 plant species, of which more than 90 percent are only found here. The endemics include five unique plant families and such emblematic species as baobab trees or the traveler's palm.

The island has very contrasting vegetation types, with a notable distinction between the west, centre, and east. While the centre is dominated by dry forests and grasslands, the east, receiving most rain from the Indian Ocean, harbours mainly tropical rainforest, and the driest part of the country in the southwest features unique spiny forests.

Human use has changed Madagascar's natural flora dramatically. Rice paddies are a common feature, and other tropical crops such as bananas, yams, cassava, and vanilla are cultivated. Deforestation is a serious problem and has led to the decline of many native vegetation types.

Its high diversity coupled with dramatic decrease of its natural vegetation makes Madagascar one of the world's biodiversity hotspots. A number of areas are protected as nature reserves.

Diversity and endemism

Vascular plants

Madagascar has been described as "one of the most floristically unique places in the world".^[1] According to the Catalogue of the Vascular Plants of Madagascar, 243 vascular plant families with roughly 11,000 species are known, of which 83 per cent are only found on the island. This includes five endemic families: Asteropeiaceae, Barbeuiaceae, Physenaceae, Sarcolaenaceae and Sphaerosepalaceae.^[2] As many as 96 per cent of Madagascan trees and shrubs were estimated to be endemic.^[3]

Ferns and lycophytes have 272 described species in Madagascar. About half of these are endemic; in the scaly tree fern family Cyatheaceae, native to the eastern humid forests, all but three of 47 species are endemic. Six conifers in genus Podocarpus—five endemic—and one cycad, Cycas thouarsii, are native to the island.^[2]

In the flowering plants, basal groups account for some 320 Madagascan species, around 94% of which are endemic. The families most rich in species are Annonaceae, Lauraceae, Monimiaceae, and Myristicaceae, containing mainly trees, shrubs, and lianas, and the predominantly herbaceous pepper family (Piperaceae).^[2]

Plants of the Madagascan humid forests
Madagascar periwinkle (Cataranthus roseus, Apocynaceae) is widely cultivated in tropical regions  Leptolaena multiflora, from the endemic family Sarcolaenaceae  Cyathea dregei is one of several tree ferns present  Nepenthes madagascariensis, one of two endemic pitcher plants

Monocots are highly diversified in Madagascar. The most species-rich plant family, orchids (Orchidaceae), fall in this lineage and have over 900 species, of which 85% are endemic. Palms (Arecaceae) have around 200 species in Madagascar (most in the large genus Dypsis), more than three times as many as in continental Africa; all but five are endemic. Other large monocot families include the Pandanaceae with 78 endemic pandan (Pandanus) species, mainly found in humid to wet habitats, and the Xanthorrhoeaceae with most species, over 130 endemics, in the dryland genus Aloe. Grasses (Poaceae, 541 species^[4]) and sedges (Cyperaceae, 314 species) are diverse, but have lower levels of endemism (40%^[4] and 37%, respectively). A national emblem and widely planted, the traveller's palm is the sole species in the genus Ravenala (Strelitziaceae), endemic to humid habitats in Madagascar.^[2]

The eudicots account for most of Madagascar's plant diversity. Their most species-rich families on the island are:^[2]

• Fabaceae (662 species/77% endemic), accounting for many trees in humid and dry forests, including rosewood.
• Rubiaceae (632/92%), with notably over 100 endemic Psychotria and 60 endemic coffee species.
• Asteraceae (533/81%), of which over 100 endemic species in Helichrysum.
• Acanthaceae (500/94%), with 90 endemic species in Hypoestes.
• Euphorbiaceae /460/94%), notably with the large genera Croton and Euphorbia.
• Malvaceae (485/87%), including the large genus Dombeya (177 species, 97% endemic) and seven out of eight baobabs (Adansonia), of which six are endemic.
• Apocynaceae (363/93%), including the Madagascar periwinkle (Catharanthus roseus).
• Melastomataceae (338/98%), mainly trees and shrubs.

A less species-rich, but very characteristic eudicot family is Didiereaceae with eleven species, only found in the spiny forests of the southwest.^[2]

Plants of dry habitats in Madagascar
Aloe divaricata (Xanthorrhoeaceae), one of the more widespread Aloe species  Didierea trollii (Didiereaceae), an endemic from the dry southwest  Euphorbia iharanae (Euphorbiaceae), an endangered succulent from the north  Pachypodium rosulatum (Apocynaceae) from the central plateaus, Isalo National Park

Mosses, liverworts, and hornworts

An checklist from 2012 record 751 moss species and infraspecific taxa, 390 liverworts, and three hornworts for Madagascar. About 34% of the mosses and 19% of the liverworts are endemic. It is unknown how many of those may have gone extinct since their discovery, and a number of species likely remain to be described.^[5]

Fungi

If fungi are included in the flora, it is assumed that many species remain to be described in Madagascar. An overview of edible mushrooms listed a number of species consumed in the country, especially from the genera Auricularia, the chanterelles (Cantharellus), and the brittlegills (Russula). Most of the ectomycorrhizal species are found in plantations of introduced eucalyptus and pine, but also in native tapia woodlands.^[6]

The pathogen Batrachochytrium dendrobatidis, responsible for chytridiomycosis which threatens amphibian populations worldwide, was long considered absent from Madagascar. It was however first recorded in 2010 and confirmed since for various areas and different frog families in the country, alerting scientists about the potential threat to Madagascar's already endangered frog fauna.^[7]

Vegetation types

Left: Land cover; note the dark green belt of humid forest along the east coast. Right: Topography.

Land cover of vegetation types in Madagascar^[8]

  Plateau grassland–wooded grassland mosaic (41.67%)

  Wooded grassland–bushland mosaic (22.93%)

  Humid forest (8.06%)

  Degraded humid forest (9.81%)

  Western dry forest (5.4%)

  South western dry spiny forest-thicket (3.1%)

  Cultivation (likely underestimated) (3.97%)

  Other (5.06%)

Madagascar features very contrasting and some unique vegetation types, determined mainly by topography, climate, and geology. A mountain range on the east, rising up to 2,876 m (9,436 ft) in some massifs, captures most rainfall brought in by trade winds from the Indian Ocean. Consequently, the eastern belt harbours most of the humid forests, while precipitation decreases to the west. The rain shadow region in the southwest has a sub-arid climate. Temperatures are highest on the west coast, with annual means of up to 30 °C (86 °F), while the high massifs have a cool climate, with a 5 °C (41 °F) annual mean locally. Geology features mainly igneous and metamorphic basement rocks, with some lava and quartzite in the central and eastern plateaus, while the western part has belts of sandstone, limestone (including the tsingy formations), and unconsolidated sand.^[8]

Authors of the 20th century noted the east–central–west distinction of the Madagascan flora and proposed several similar classifications.^[1] The "Atlas of the Vegetation of Madagascar" (2007) distinguishes 15 vegetation types based on satellite imagery and ground surveys; these are defined by their physiognomy and can have different species composition in different parts of the island.^[8] They partly correspond to the terrestrial ecoregions identified by the World Wildlife Fund (WWF) in Madagascar.^[9]

Humid forest

This tropical rainforest covers around 8 percent of the island, but used to encompass more than twice as much. It ranges from sea level to 2,750 m (9,020 ft) elevation and is mainly found on the eastern plateaus, on basement rocks with lateritic soils. Annual rainfall is 1,500–2,400 mm (59–94 in); the dry season short or absent. The mainly evergreen forest, up to 35 m high (115 ft), is composed of diverse tree and understory species from various families such as Burseraceae, Ebenaceae, Fabaceae, and Myristaceae; bamboos and lianas are frequent.^[8] The WWF classifies the eastern belt, below 800 m (2,600 ft) elevation, in the Madagascar lowland forests and the montane forests of the central highlands in the Madagascar subhumid forests.^[9]

Degraded humid forest

This altered, secondary form of humid forest—savoka in Malagasy—covers ca. 10 percent of the island's area. It spans various states of degradation and is composed of forest remnants and planted or otherwise introduced species. It is primarily the result of slash-and-burn cultivation in primary forest. Some forest fragments still harbour a considerable amount of biodiversity.^[8]

Littoral forest

Found in several isolated areas along the eastern coast, this forest type covers less than 1 percent of the land area, on mainly sandy sediments. Climate is humid, with 1,300–3,200 mm (4.3–10.5 ft) annual rainfall. Littoral forest covers sandy soil forest, marsh forest, and grasslands. Its flora includes various tree families, lianas, and epiphytic orchids and ferns; in the marsh forests, pandans (Pandanus) and the traveler's palm (Ravenala madagascariensis) are common.^[8]

Wooded grassland–bushland mosaic

This diverse mixture of different vegetation types covers roughly 23 percent of the surface. It ranges from sea level to 2,700 m (8,900 ft) elevation and is mainly found on the western and central plateaus and their escarpments, but also in areas of cleared vegetation in the south and east. Substrates are basement rock, sandstone, and lava, and climate ranges from sub-humid to sub-arid. The flora has been strongly modified through human-induced fires and grazing, and includes exotic species such as plantations of pine, eucalypt, and cypress. At higher altitudes on thin soil, there is an indigenous, sclerophyllous vegetation that includes Asteraceae, Ericaceae, Lauraceae, and Podocarpaceae shrubs, among others.^[8] These forests and thickets on the high massifs are singled out by the WWF as Madagascar ericoid thickets.^[9]

Plateau grassland–wooded grassland mosaic

This most widespread type covers about 42 percent of the island in the west and the central plateaus, ranging from sea level to 2,700 m (8,900 ft). Geological substrate is variable but mainly igneous and metamorphic in the central highlands. Climate is equally variable, ranging from sub-humid to sub-arid, with rainfall between 300 millimetres and 3,300 millimetres (12 in and 10.8 ft) per year. It is supposed to be of human origin in most parts, created and maintained through fire and grazing. Grasses, mainly Loudetia simplex and the endemic Aristida rufescens, are dominating the grassland parts, while wooded parts include native and introduced trees.^[8]

Tapia forest

This evergreen forest type is found on the western and central plateaus, at altitudes of 500–1,800 m (1,600–5,900 ft). It covers less than one percent of the surface. The broad regional climate is sub-humid to sub-arid, but tapia forest is mainly found in drier microclimates. Trees include Uapaca bojeri, Asteropeiaceae, Sarcolaenaceae, and others, with a herbaceous understory. Tapia forest is subject to human pressure, but relatively well adapted to fire.^[8] The WWF includes tapia forests in Madagascar subhumid forests.^[9]

Western humid forest

Confined to a very small plateau region in the south west, on the eastern slope of the Analavelona massif, on lavas and sand, at 700–1,300 m (2,300–4,300 ft) elevation. This isolated humid forest is maintained through condensating moisture from ascending air. The forest is unprotected but the local population considers it sacred.^[8] The WWF includes it in Madagascar subhumid forests.^[9]

Western dry forest

Accounting for roughly 5 percent of the surface, Western dry forest is found in the west, from the northern tip of the island to the Mangoky river in the south. It ranges from sea level to 1,600 m (5,200 ft) in elevation. Climate is sub-humid to dry, with 600–1,500 mm (24–59 in) annual rainfall and a dry season of around six months. Geology is varied and can include limestone forming the eroded tsingy outcrops. Vegetation is diverse; it ranges from forest to bushland and includes trees of the Burseraceae, Fabaceae, Euphorbiaceae, and baobab species.^[8] The WWF classifies the northern part of vegetation as Madagascar dry deciduous forest and the southern part, including the northernmost range of Didiereaceae, as Madagascar succulent woodlands.^[9]

Western sub-humid forest

This forest occurs inland in the south west and covers less than 1 percent surface, mainly on sandstone, at 70–100 m (230–330 ft) elevation. Climate is sub-humid to sub-arid, with 600–1,200 mm (24–47 in) annual rainfall. The vegetation, up to 20 m tall (66 ft) with a closed canopy, includes diverse trees with many endemics such as baobabs (Adansonia), Givotia madagascariensis, or the palm Ravenea madagascariensis. Cutting, clearing and invasive species such as opuntias and agaves threaten this vegetation type.^[8] It is part of the WWF's Madagascar subhumid forests.^[9]

Examples of native vegetation in Madagascar
Humid forest, Masoala National Park  Plateau wooded grassland with the endemic Bismarck palm (Bismarckia nobilis), Isalo National Park  Tsingy limestone formations and Western dry forest, Ankarana Reserve  Spiny forest, with baobabs (Adansonia sp.) and Madagascar ocotillo (Allaudia procera), near Ifaty

South western dry spiny forest-thicket

This vegetation type unique to Madagascar covers ca. 3 percent of its area. It is confined to the sub-arid region in the southwest, at an elevation of up to 300 m (980 ft), on limestone and sandstone bedrocks. Mean annual rainfall is about 540 mm (21 in), and the rain season very short. It is a dense thicket composed of plants adapted to dry conditions, notably through succulent stems or leaves transformed into spines. The characteristic plants are the endemic Didiereaceae family, baobabs, and Euphorbia species.^[8] The WWF classifies it as Madagascar spiny thickets.^[9]

Degraded south western dry spiny forest

Degraded spiny forest accounts for ca. one percent of the surface in the southwest. It results from cutting, clearing, and encroachment. Introduced species associated to disturbed areas, such as Agave and Opuntia, are found in addition to remnants of the native flora.^[8]

South western coastal bushland

Located in the same larger southwest region as the spiny forest, this formation is only found along the coast, at an elevation of 0–50 m (160 ft). Climate is sub-arid, with only 370–380 mm (15–15 in) of rainfall per year, concentrated in one month or less. The substrate is mainly unconsolidated sediment. This vegetation type is an open bushland without closed canopy. It is dominated by several tree and shrubs, including Euphorbia species.^[8]

Wetlands

Wetlands cover roughly one percent of the island, not counting running water. Marshes, swamp forests and lakes are found in all regions, along with rivers and streams. Typical species of wet habitats are several endemic Cyperus sedges, ferns, pandans (Pandanus), and the traveller's palm (Ravenala madagascariensis). Two species of water lilies, Nymphaea lotus and Nymphaea stellata, are found in the west and east, respectively. Lagoons are mainly found on the east coast, but also occur in the west. Salty and brackish habitats have a specialised flora, including Chara zeylanica, Salicornia pachygastra, and some grasses. Peat bogs are restricted to highlands above 2,000 m (6,600 ft) elevation; their distinct vegetation includes, among others, Sphagnum moss and sundew species (Drosera). Many wetlands have been converted into rice paddies and are otherwise threatened by destruction and pollution.^[8]

Mangroves

Mangrove forests occur on the eastern, Mozambique channel coast, from the very north to just south of the Mangoky river delta. Eleven mangrove tree species are known from Madagascar. The most frequent belong to the families Acanthaceae, Lecythidaceae, Lythraceae, Combretaceae, and Rhizophoraceae. Mangrove forests are threatened by encroachment and cutting.^[8] The WWF lists them as Madagascar mangroves ecoregion.^[9]

Cultivation

Cultivation accounts for at least 3.9 percent of the surface, but its real extent is difficult to estimate. It includes especially rice fields, and there are plantations of sisal as well as pine and eucalyptus. Other important crops are cassava, sweet potatoes, sugar cane, coffee, and vanilla.^[8]

Rice paddies near Ambalandingana, central plateau

Origins and evolution

The prehistoric breakup of the supercontinent Gondwana separated the Madagascar-Antarctica-India landmass from the Africa-South America landmass around 135 million years ago. Madagascar later split from India about 88 million years ago, allowing plants and animals on the island to evolve in relative isolation.^[10]

Its distinctive ecology has led some ecologists to refer to Madagascar as the "eighth continent".^[11]

Human use

Humans have made use of Madagascar's flora ever since the island has been colonised, and heavily impacted its landscape through turning natural vegetation into farmed land. Rice paddies mark the landscape over much of the island, as rice is the staple food of the population.

Many native plant species are used as herbal remedies for a variety of afflictions. The drugs vinblastine and vincristine, used to treat Hodgkin's disease, leukemia and other cancers, were derived from the Madagascar periwinkle.^[12]

Threats and conservation

Habitat destruction threatens many of Madagascar's endemic species and has driven others to extinction. In 2003 Ravalomanana announced the Durban Vision, an initiative to more than triple the island's protected natural areas to over 60,000 km² (23,000 sq mi) or 10 percent of Madagascar's land surface. As of 2011, areas protected by the state included five Strict Nature Reserves (Réserves Naturelles Intégrales), 21 Wildlife Reserves (Réserves Spéciales) and 21 National Parks (Parcs Nationaux).^[13] In 2007 six of the national parks were declared a joint World Heritage Site under the name Rainforests of the Atsinanana. These parks are Marojejy, Masoala, Ranomafana, Zahamena, Andohahela and Andringitra.^[14] Local timber merchants are harvesting scarce species of rosewood trees from protected rainforests within Marojejy National Park and exporting the wood to China for the production of luxury furniture and musical instruments.^[15] To raise public awareness of Madagascar's environmental challenges, the Wildlife Conservation Society opened an exhibit entitled "Madagascar!" in June 2008 at the Bronx Zoo in New York.^[16]

The island has been classified by Conservation International as a biodiversity hotspot.^[17]

See also

• Wildlife of Madagascar

References

1. Gautier, L.; Goodman, S.M. (2003). "Introduction to the Flora of Madagascar". In Goodman, S.M.; Benstead, J.P. The Natural History of Madagascar. Chicago, London: The University of Chicago Press. pp. 229–250.
2. "Catalogue of the Vascular Plants of Madagascar". Saint Louis, Antananarivo: Missouri Botanical Garden. 2009–2016. Retrieved 28 March 2016.
3. Schatz, G.E. (2000). "Endemism in the Malagasy tree flora". In Lourenço, W.R.; Goodman, S.M. Diversité et endémisme à Madagascar/Diversity and endemism in Madagascar. Biogéographie de Madagascar 2. Bondy: ORSTOM Editions. pp. 1–9. ISBN 2-903700-04-4. (English/French)
4. Vorontsova, M.S.; Besnard, G.; Forest, F.; Malakasi, P.; Moat, J.; Clayton, W.D.; Ficinski, P.; Savva, G.M.; Nanjarisoa, O.P.; Razanatsoa, J.; Randriatsara, F.O.; Kimeu, J.M.; Luke, W.R.Q.; Kayombo, C.; Linder, H.P. (2016). "Madagascar's grasses and grasslands: anthropogenic or natural?". Proceedings of the Royal Society B: Biological Sciences 283 (1823): 20152262. doi:10.1098/rspb.2015.2262. ISSN 0962-8452.
5. Lovanomenjanahary, M.; Andriamiarisoa, R.L.; Bardat, J.; Chuah-Petiot, M.; Hedderson, T.A.J.; Reeb, C.; Strasberg, D.; Wilding, N.; Ah-Peng, C. (2012). "Checklist of the Bryophytes of Madagascar". Cryptogamie, Bryologie 33 (3): 199–255. doi:10.7872/cryb.v33.iss3.2012.199. ISSN 1290-0796.
6. Buyck, Bart (2008). "The Edible Mushrooms of Madagascar: An Evolving Enigma". Economic Botany 62 (3): 509–520. doi:10.1007/s12231-008-9029-4. ISSN 0013-0001.
7. Bletz, M.C.; Rosa, G.M.; Andreone, F.; Courtois, E.A.; Schmeller, D.S.; Rabibisoa, N.H.C.; Rabemananjara, F.C.E.; Raharivololoniaina, L.; Vences, M.; Weldon, C.; Edmonds, D.; Raxworthy, C.J.; Harris, R.N.; Fisher, M.C.; Crottini, A. (2015). "Widespread presence of the pathogenic fungus Batrachochytrium dendrobatidis in wild amphibian communities in Madagascar". Scientific Reports 5: 8633. doi:10.1038/srep08633. ISSN 2045-2322.
8. Moat, J.; Smith, P. (2007). Atlas of the Vegetation of Madagascar/Atlas de la Végétation de Madagascar. Richmond, Surrey: Royal Botanic Gardens, Kew. (English/French)
9. Burgess, N.; D'Amico Hales, J.; Underwood, E.; Dinerstein, E. (2004). Terrestrial Ecoregions of Africa and Madagascar: A Conservation Assessment. World Wildlife Fund Ecoregion Assessments (2nd ed.). Washington D.C.: Island Press. ISBN 978-1559633642.
10. University of Berkeley: Understanding Evolution (October 2009). "Where did all of Madagascar's species come from?". Archived from the original on 19 March 2011. Retrieved 19 March 2011.
11. Hillstrom & Collier Hillstrom (2003), p. 50
12. Foster, Steven (December 2010). "From Herbs to Medicines: The Madagascar Periwinkle's Impact on Childhood Leukemia: A Serendipitous Discovery for Treatment". Alternative and Complementary Therapies 16 (6): 347–350. doi:10.1089/act.2010.16609.
13. Madagascar National Parks (2011). "The Conservation". parcs-madagascar.com. Archived from the original on 25 August 2011. Retrieved 25 August 2011.
14. "Rainforests of the Atsinanana". UNESCO. Archived from the original on 25 August 2011. Retrieved 30 April 2011.
15. Bearak, Barry (24 May 2010). "Shaky Rule in Madagascar Threatens Trees". New York Times. Archived from the original on 20 March 2011. Retrieved 20 March 2011.
16. Luna, Kenny. "Madagascar! to Open at Bronx Zoo in Green, Refurbished Lion House". Treehugger. Archived from the original on 10 July 2011. Retrieved 11 June 2011.
17. Conservation International (2007). "Madagascar and the Indian Ocean Islands". Biodiversity Hotspots. Conservation International. Archived from the original on 24 August 2011. Retrieved 24 August 2011.

Bibliography

• Hillstrom, Kevin; Collier Hillstrom, Laurie (2003). Africa and the Middle East: a continental overview of environmental issues. Santa Barbara, CA: ABC-CLIO. ISBN 978-1-57607-688-0.