Madagascar and other Islands
The Biological Wealth of an Impoverished Country: Forests and Plants Madagascar has one of the richest floras in the world. Eighty percent of its plants are found nowhere else (McNeely et al. 1990, Preston-Mafham 1991). The diversity of plants that survived almost 2,000 years of forest destruction continues to astound biologists and conservationists. Tropical trees with fruit growing on their trunks (various species of the genus Tambourissa) are native, as is a cactus (Rhipsalis), related to American species, that lives in the rainforest. A tree, Symphonia, which has leathery leaves and red-and-white striped flowers that look like peppermint candies (Morell 1999), also survives. The Flame Tree (Delonix regia), which produces cascades of red flowers, is grown around the world for its beauty, but few realize that it originated in Madagascar (Preston-Mafham 1991). Miraculously, many endemic plants have survived the fires and tree cutting that have destroyed much of the island. One mountain chain has 150 endemic vascular plants, a very high number (Preston-Mafham 1991). They are among the 7,300 to 12,000 species of plants native to Madagascar (Preston-Mafham 1991). Its flowering plants make up 20 percent of all the plants in the African region (McNeely 1990). At least 191 botanical families, a very large number for a relatively small area, evolved from ancestor species (Preston-Mafham 1991).
Some 2,000 years ago, the eastern rainforest stretched in a band 100 miles wide from north to south, covering 27 million acres (Tyson 2000). Ninety percent of the plants were endemic, with a profusion of unusual ferns, some types growing on tree trunks; wild ginger, with delicate purple flowers; bamboos; and far more orchids than in an African rainforest (Preston-Mafham 1991). An early traveler described the woods as so dense that there was a “deep gloom: below the canopy at mid-day (Tyson 2000). Rainfall must have been greater and general climate more humid than at present as a result of these extensive rainforests. In the montane ridges, huge tree ferns, mosses and lichens cover the ground and hang from tree branches (Preston-Mafham 1991). Over the centuries, Malagasy burned many portions of the rainforest, especially in the south. Few tall trees remain in the rainforest today, although at one time there must have been many giants. During the 19th century, a palace was built for a woman ruler, centering on a 130-foot tree that had been carried by 5,000 laborers from the eastern rainforest (Tyson 2000). The palace was destroyed by an uprising in the 1850s. About this time, Malagasy dragged a tombstone through the forest, cutting 25,000 trees just to make a path (Tyson 2000). Early decrees banned cutting of virgin forest, with severe penalties, in the 19th century, but these were largely ignored (Tyson 2000).
About half of the island's forests had been cut by the late 19th century, and intensive cutting continued in the 20th century (Tyson 2000). The prime lowland forests throughout the island and three-fourths of the rainforest were cleared by the French for growing coffee and other crops in the first three decades of the century (Tyson 2000). The rainforest was heavily logged between 1950 and 1985, with 275,000 acres cleared and burned each year (Tyson 2000). The northeast Masoala Peninsula still retains sizeable areas of unlogged rainforest, but the southern region has been reduced to fragments of the original unbroken expanses. The remnants tend to be on sharp ridges where soil is poor and access difficult. For example, Ranomafana, a recently declared national park, straddles such an escarpment. Even so, many of its trees had been removed prior to its protection (Tyson 2000). What was once a closed-canopy, humid rainforest is now far dryer and cooler, with many openings among the trees, and some illegal logging continues (Tyson 2000). Still, botanists from the Missouri Botanical Garden, who were conducting a census of the trees in this park, counted 37 families of trees with 105 species in a 1-hectare plot (Tyson 2000). Outside the park's boundaries, rainforest is still being cleared and burned by the Malagasy, many of whom believe that their wealth lies in the amount of land they clear (Morell 1999).
The western dry, deciduous forest lies in the shadow of eastern mountains, which block moist ocean air currents (Preston-Mafham 1991). Trees do not attain heights of more than 80 feet, but many types of plants have adapted to this environment. Liana vines grow among the trees, and dead leaves carpet the forest floor. Large tamarind trees grow along rivers, and baobabs grow in plateaus (Preston-Mafham 1991). Beautiful orange bell flowers of the Ipomoea carnea plant burst into bloom during the short rainy season. As with the eastern rainforests, the once continuous stretches of deciduous forests have been largely destroyed, replaced by grasses able to survive in the eroded or bare soil.
Throughout the island, most deforested areas fail to regenerate into second-growth forests, even when left fallow, because Madagascar lacks vigorous colonizing trees that can quickly protect cleared ground and prevent further erosion (Preston-Mafham 2000). Cleared hillsides become covered in non-native grasses and exotic South American trees (Psidium cattleyanum and Psidium guajava) or plantations of eucalyptus, which inhibit the establishment of native seedlings (Preston-Mafham 1991; Sayer et al. 1992). Only if soils are rich and remnants of original forest are nearby will native forests regenerate. Unfortunately, the original forests and their native wildlife are lost permanently, and even regeneration cannot take place without a cessation of the slash-and-burn cycle, known as “tavy” by the Malagasy (Preston-Mafham 1991). Moreover, foreign logging companies have obtained logging concessions on most of the unprotected remnants of native forest. Tree cutting consumes some 7.8 million cubic meters of wood per year, of which 7 million cubic meters is for fuel and charcoal (Sayer et al. 1992). Valuable timber trees have been logged to extinction in most of Madagascar. The two native species of ebony trees of the genus Diospyros have been heavily logged for centuries, and few large trees are left (Sayer et al. 1992). The understory plants, such as tree ferns, are also exploited, dug up to sell as potted plants (Sayer et al. 1992).
The net result of this logging and burning, especially in the barren central highlands, is the loss of "a priceless reservoir of plant and animal species, replaced by one of the most impoverished forms of vegetation on the planet" (Preston-Mafham 1991). Many species of trees and other plants are highly endangered. Madagascar is one of the world's 12 "hot spot" areas of tropical forests, having a high percentage of endemic species which are under great threat (McNeely et al. 1990). Since an estimated 94 percent of Madagascar's trees are endemic, and many occupy very restricted ranges, they are highly vulnerable to extinction. Further research will likely reveal even more threatened species. Some authorities believe that even this rich plant diversity must represent only a fraction of the "vast original flora," since 80 percent of the vegetation and forests is gone (Ayensu et al. 1984). The 1997 IUCN Red List of Threatened Plants includes 19 species of plants that may have recently become extinct, and an additional 287 species that are threatened with extinction (Walter and Gillett 1998).
Resident since the days of the dinosaurs, trees of a family of primitive pines, Podocarpaceae, grow on the island. The family is represented by species in other parts of the world that were part of Gondwana, from South America west to Southeast Asia. Madagascar has a number of native Podocarps, of which four endemic species or varieties are listed by the IUCN Red List as either Vulnerable or Rare (Walter and Gillett 1998). At least 26 genera of plants are native to Madagascar and South America, but not to Africa, and are believed to be remnants from Gondwana (Preston-Mafham 1991). Another one of these, Madagascar's national tree, the Traveller's Tree (Ravenala madagascariensis), is a palm-like species of the banana family (Musaceae). Its closest relative of the same genus grows in Brazil and Guiana, but not in Africa (Preston-Mafham 1991). This tree has leathery petals covering its pollen and nectar and is a key food source for both bats and lemurs. In return, it depends on lemurs for pollination. Lemurs feed on the nectar, getting their noses covered with pollen in the process. They are so fond of the nectar that they travel miles to find another Traveller's Tree, still carrying the nectar on their noses and, unknowingly, pollinate the next tree they feed on (Attenborough 1995).
A plant of the Winteraceae family that has been growing on the island for 30 million years was recently seen again after a period of 90 years (Hsu 1997). This tree, Takhtajania perrieri, has many primitive features, such as a lack of vessels to move water and minerals; like many of Madagascar's relict species, it once grew on much of continental Africa, but long ago disappeared there (Hsu 1997).
Madagascar has more palms (Palmae family) than all of Africa (Preston-Mafham 1991). Many are in danger, however. The IUCN Red List of Threatened Plants lists 148 native species in various categories (Walter and Gillett 1998). The Big-leaf Palm (Marojeya darianii) was chosen by the Species Survival Committee of the IUCN to be one of 12 critically endangered species highlighted at its 1988 General Assembly in Costa Rica. This species was only discovered in 1982 and is confined to a single swamp in the northeast (Prance 1990). An agricultural program to raise rice cleared half its habitat, and then failed. This huge-leafed palm has been over-harvested as a source of heart-of-palm, a commercially valuable product (Prance 1990). Huge palms are felled for their inner pith to supply this gourmet market. The majority of palms grow in the eastern rainforests in a great diversity of size. Two threatened palms, Dypsis hildebrandtii and Dypsis louvelii, are miniature delicate-fronded palms only 3 feet high (Preston-Mafham 1991). Others, like the threatened Ravenea glauca, are majestic giants with long, straight trunks rising 50 feet or more to a luxuriant crown. Palms do not often survive the fires set by the Malagasy to clear land, disappearing from one area after another (Preston-Mafham 1991).
On the entire continent of Africa, only one species of baobab tree is native, while seven species are found in Madagascar (Preston-Mafham 1991). These strange-looking trees have wide trunks that taper to a narrow crown, looking like upside-down trees. Some baobabs grow to immense size. One famous specimen measures 46 feet around the base of the trunk (Preston-Mafham 1991). Another species, Alluaudia ascendens, grows in the southern desert. Although it can reach a maximum height of 16 feet, it is usually far smaller (Preston-Mafham 1991). Each of the seven species has a slightly different shape and size, but all have gray bark that resembles unwrinkled elephant skin. Baobabs are extremely important to both wildlife and humans. The Malagasy cut holes in their massive trunks and hollow out the spongy pith where water accumulates. In the dry south, these trees become wells, and villagers set ladders against the trunks, climb to the hole cut from the trunk, and lower buckets into the pool of water. Natural holes in baobob trunks and branches provide important nesting holes for birds and lemurs. These trees are fire-resistant, and fortunately, they are worthless as timber because of their soft, pulpy cores. For this reason some stands of thousands of huge, very old baobabs remain in parts of the island. Because of the heavy livestock grazing, few young baobab seedlings can survive, however, and botanists believe that the spectacular vistas of these behemoths will gradually disappear (Preston-Mafham 1991).
One very strange group of Madagascan plants native to dry areas has nine species in the same genus, Pachypodium. These succulent plants lose their leaves at the onset of the dry season and have evolved into a variety of forms, all with gray, smooth bark. Eight of the nine species are threatened with extinction, according to the IUCN Red List of Threatened Plants (Walter and Gillett 1998). One of these, the endangered Pachypodium decaryi, is native to Antananarivo, the "tsingy" limestone crags of the northwest. Its smooth, silvery trunk resembles a large inverted turnip, fat at the base and tapering upward, topped by a messy mop of thin, straggly branches (Preston-Mafham 1991). It bears large, white flowers during the dry season. Its main population occurs in the Ankarana Special Reserve, which bans burning (Preston-Mafham 1991), but has recently been invaded by hordes of miners who are clearing vegetation to search for sapphires (Morell 1999). Other Pachypodiums have equally bizarre shapes, such as the bulbous Pachypodium rosulatum, which resembles a huge gourd sprouting long, thin shafts from which its bright yellow flower bloom. The rare Pachypodium densiflorum, with the appearance of a domestic jade plant run amok, has a mass of short, gray branches sprouting from a squat gray base. All these plants are highly susceptible to fire. Ken Preston-Mafham, in Madagascar: A Natural History, describes the threat of "incessant brush fires which ravage the length and breadth of central Madagascar during the dry season. Within hours, hillsides which had been decorated with colorful rock gardens of rare succulents are converted into graveyards of charred embers." These brush fires have been intentionally set by Malagasy to improve grazing land for their cattle or clear land. Another threat to Pachypodia is collectors who tear specimens, especially bizarre forms, from mountain slopes (Preston-Mafham 1991). Few species are protected in reserves. Without strong conservation programs, these fascinating plants could easily disappear.
Other strange trees of the southern spiny desert include the Octopus Tree (Didierea madagascariensis), a member of an endemic family of 11 cactus-like species, Didiereaceae. This tree has no trunk, but a bouquet-like grouping of stems covered in long, needle-sharp spines that branch out in odd, twisted shapes. Although resembling cacti, this family has no close relatives anywhere in the world (Preston-Mafham 1991). Another member of the family, Alluaudia procera, has a thick trunk with very long spines that grow in curving rows upward, and small, rounded leaves along its branches. In spite of this, several lemur species are able to leap onto these plants without hurting themselves (Preston-Mafham 1991). Three species in this family, all of the Alluaudia genus, are Rare, according to the IUCN (Walter and Gillett 1998). One of these, Alluaudia montagnacii, has tall, solitary tapering stems ending in a tuft of flowers.
The discovery of the medicinal effects of the endemic Rosy Periwinkle (Catharanthus roseus) has saved thousands of human lives. Two potent alkaloid compounds found in this plant have proven effective in the treatment of Hodgkin’s' Disease, producing a 99 percent remission in patients with acute lymphocytic leukemia (Myers 1983). It also contains 75 different alkaloids, which could produce commercial substances (Preston-Mafham 1991). Fortunately, the Rosy Periwinkle is easy to propagate, grown in greenhouses around the world. Ongoing research is uncovering other Madagascan plants of medicinal value. Samples of plants are being tested in laboratories, and elderly Malagasy healers are being consulted. More than 50 species of wild coffee (Coffea spp.) grow in the island's eastern rainforests, providing an important genetic base for hybridizing with other strains because of their insect-resistance and low level of caffeine (Preston-Mafham 1991). These plants are symbolic of the great botanical wealth at risk.