It's Too Late
Plants Extinctions of plants and trees can have a direct impact on human society. A sap found in 1997 by Dr. John Burley, research director of Harvard University's Arnold Arboretum, was tested by the National Cancer Institute and determined to be 100 percent effective in preventing cell replication of the AIDS virus (Stocker 1996). The plant sample came from an ancient swamp forest tree in Sarawak, a Malaysian state on the island of Borneo. When Dr. Burley returned to the spot a year later for another specimen from the tree, only a stump remained, and no other trees of the same species could be found (Stocker 1996). The substance is being reproduced synthetically, but it is not known whether it will be as effective as the original compound (Stocker 1996).
Sarawak's forests grew undisturbed for 180 million years, but they are now rapidly disappearing along with the rest of Borneo's ancient forests. Commercial loggers have felled tens of thousands of these old growth, towering trees in Indonesia and other tropical rainforests for the manufacture of disposable packing crates and chopsticks for Japanese and Chinese markets. Borneo's forests are also being consumed by fires set by wealthy landowners to clear land for palm plantations, or by settlers for farmland, eliminating an untold number of plants. Some tropical tree species have wide distributions over thousands of square miles, but many occupy extremely small areas. This was dramatically illustrated in the disappearance of this tree. Thousands of compounds that could cure diseases or be of great economic and ecological importance may be lost on a daily basis as the world's forests are destroyed at this unprecedented rate.
Plant extinctions have accelerated in the past few centuries. An estimated 5,050 taxa of plants, including species, varieties and other taxonomic groups, have become extinct worldwide since 1700, according to Ghillean T. Prance of the Royal Botanical Gardens Kew (Prance 1990). This implies at least 17 plants have been lost per year since 1700. Yet however high this rate appears to be, it is probably a low estimate. A 1998 study by botanists Kerry S. Walter and Harriet J. Gillett for the International Union for the Conservation of Nature (IUCN) found that 380 species, a number that does not include varieties and other taxa, have recently become extinct. These authors admit their extinction total may be low as a result of lack of data, and they did not define the time period covered.
· The data lacks exact numbers of plant extinctions. Plants rarely leave signs of their existence as vertebrates do, since bones are the basis of much data on animal extinctions. Non-woody plants, which make up the majority of plants, leave little trace when they die, and are soon consumed by microbes. This is especially true in tropical areas, where plant matter is consumed very quickly. We know of ancient plants by chance events, such as the preservation of pollen grains or other plant parts in peat, mud, amber or fossilized stone. When numbers of plant extinctions are estimated, the diversity and status of habitat are important considerations. Moreover, only a small percentage of all plants have been scientifically described. What is known is a great many regions of the Earth that once had very diverse endemic plants have been destroyed within the past few centuries, and a majority was not thoroughly assessed.
Botanical wealth is often discovered and destroyed soon after. In Ecuador's mountain ridges, botanists Al Gentry and Calaway Dodson of the Missouri Botanical Garden in St. Louis discovered many unique plants in 1978 on a crest known as Centinela Ridge in a 20 square kilometer cloud forest in the foothills of the Andes. Among the plants were 38 endemic species, many of which were unusually dark‑leafed (Forsyth 1990). The two scientists found a total of 90 related plants growing under the forest canopy with epiphytic plants, such as bromeliads and orchids, on the trunks and branches of the trees (Wilson 1992). These cloud forests and paramos ‒ treeless, mossy areas in the northern Andes ‒ are centers for unique species. At the time they discovered the plants, Gentry and Dodson observed farmers from the valley below clearing the forests, as they have done on 96 percent of the Pacific ridges of the Andes (Wilson 1992). Gradually, the clearing moved up to Centinela Ridge. By 1986, the botanical oasis had disappeared; in its place were cacao and other crops (Wilson 1992). These lost species might have provided compounds to treat cancers, or been an ancestor of an agricultural plant, such as a perennial tomato, but they exist now only as pressed specimens taken by the botanists.
Near Centinela Ridge is Rio Palenque; once an extensive cloud forest, it is now diminished. It was among the most botanically diverse forests in the world — 600 species per square kilometer (Forsyth 1990). Ornithologists and birdwatchers came from all over to see the 336 bird species of Palenque's diverse habitats (Forsyth 1990). The endangered harpy eagle was one spectacular native bird that disappeared when the forest was cleared (Forsyth 1990).
Cloud forests are found in tropical Asia, Africa and Latin America. These ecosystems shelter such rarities as the iridescent green and red resplendent quetzal of Central America, but this ecosystem has nearly disappeared. An impressive variety of orchids, mosses and dwarf trees grow in these misty, cool environments. Should global warming continue, cloud forests will be among the first type of forest to disappear altogether, extinguishing thousands of unique life forms in the process.
Introduction of alien species of plants can overwhelm native species and cause their extinction (Prance 1990). In Indonesia, a type of non-native grass called imperata (Imperata cylindrica) grows aggressively in deforested areas, spreading into forests. Once established, imperata obstructs the regeneration of native plants and trees (Prance 1990), many of which exist nowhere else. Imperata has also displaced endemic plants in other parts of the world. In Australia, exotic plants are a major factor; they have eliminated at least 117 plant taxa and endangered another 1,931 (Prance 1990). Ironically, native Australian plants have caused extinctions after they became established in parts of South Africa and the Florida Everglades.
Plants have also disappeared as a result of pollution in the form of acid rain caused by power plant emissions, heavy metal (especially lead) accumulations and other toxins in the air (Prance 1990). Forests in North America and Eurasia have been susceptible to pollution, and in some areas, all forms of vegetation have died out.
Livestock overgrazing is responsible for the extinctions of countless plants, and endemic island species are among the most vulnerable. Such plants may occupy only a few acres. The South Atlantic island of St. Helena lost at least 10 kinds of endemic trees after the introduction of goats onto the island in 1513; the St. Helena redwood (Trochetia erythroxylon) became reduced to a single tree in the wild (Prance 1990). Fortunately, it was saved by propagation at the Royal Botanic Gardens Kew in London and cultivated specimens have been reintroduced (Prance 1990). The sandalo (Drypetes caustica), a fragrant type of sandalwood tree that once grew abundantly on the island of Juan Fernandez, the site of Robinson Crusoe, became extinct by 1916 after centuries of heavy logging and destruction of seedlings by goats (Prance 1990).
The Mascarene Islands, east of Madagascar in the southern Indian Ocean, have been the scene of many plant extinctions. One of the three main islands, Mauritius, was home to the famous dodo. Ebony once covered the plains and mountain slopes of this island, but during colonization of the islands from the early 17th century onward by Holland, France and Britain, extraction of a huge volume of timber denuded valleys and all accessible places (Parnell et al. 1986). As early as 1671, Mauritius had appointed a chief woodcutter to oversee the cutting of the island's forests. Unfortunately, this had little effect on forest clearance. Of the dense tropical evergreen forests that once covered the lowlands, only a few patches remain in inaccessible areas. Trees 20 meters or more in height grew in the uplands of the island, their branches heavy with thick growths of lianas and orchids. On the ground, ferns and mosses sprung up luxuriantly.
Today, only a single tract remains of this habitat, the Black River Gorges reserve (Sayer et al. 1992). By 1874, these islands, once described as verdant "earthly paradises," were dry and comparatively barren, with a vegetation composed mainly of weeds (Parnell et al. 1986). Only about 30 square kilometers of Mauritius forest survives since 93 percent was destroyed (Sayer et al. 1992). The mangrove forests that once lined Mauritius' shores have disappeared along the West Coast because they were cut for firewood. Rodrigues, a small island off the coast of Mauritius that was once a wildlife haven, lost virtually all its forests. Reunion, the third island, was also settled and heavily logged. About 61 percent of its forests, including virtually all its lowland forests, have been cleared; only 100 square kilometers remain (Sayer et al. 1992). A few remnants of montane forest have been protected by the French government, which controls the island.
Mauritius, Rodrigues and Reunion have lost many native plant species. Of 1,296 native plants, 53 species are extinct and 393 of the surviving species are threatened, according to the 1997 IUCN Red List of Threatened Plants (Walter and Gillett 1998). Little remains of its ebony forests, and eight ebony tree species are virtually extinct (Simon 1995). The islands have lost six of their beautiful orchid species, and 13 more are threatened (Walter and Gillett 1998). Mauritius and Rodrigues have been described as the "Islands of the Living Dead" by authors Beverly and Stephen Stearns because at least 30 plant species have ceased reproducing in the wild, living on the edge of extinction (Stearns and Stearns 1999). One, Ramosmania heterophylla, described in 1874, was not seen again until 1982 when botanist Wendy Strahm found the last specimen growing by a roadside. She fenced it off to protect it, only to learn this made local people consider it a "magic plant" that cured all diseases and maladies (Stearns and Stearns 1999). They cut off small pieces — despite its fencing — and have nearly obliterated it. Luckily Strahm took cuttings and sent one to Kew Gardens in England for propagation; it now grows there, but does not seed because the plant is defective (Stearns and Stearns 1999). A critically endangered tree, Elaeocarpus bojeri, native to Mauritius, has delicate, bell-like flowers with a scalloped fringe. Strahm's photograph illustrating these flowers appears on the cover of the 1997 IUCN Red List of Threatened Plants (Walter and Gillett 1998). It epitomizes the status of many Mascarene plants in need of dramatic rescue programs, as well as the need to prevent extinctions, such as that of a rare Rodrigues tree hibiscus (Hibiscus liliflorus); the species became extinct in 1982 after it was reduced to a single plant growing on the top of a mountain (Stearns and Stearns 1999).
Two endangered native wild coffee plants of Mauritius (Coffea macrocarpa and Coffea myrtifolia) might invigorate domestic species stricken with disease if they are protected from extinction, illustrating another reason to preserve native plants. The wild ancestors of domestic grains and crops retain many characteristics lost in cultivated varieties, such as resistance to drought, insects and disease. An outbreak of cornleaf blight in the United States in 1970 cost farmers almost $1 billion, and the disease was not halted until a wild corn species was interbred with the domestic strain (Fenyvesi 1995). A perennial variety of maize (wild corn) found in a Mexican forest could be hybridized with domestic corn to save farmers from replanting each year. Other crops saved by crossbreeding with tropical forest wild stock include sugarcane, coffee, cocoa and banana (Schreiber et al. 1989). Yet with the accelerating rate of plant extinctions and destruction of native plant ecosystems, many such ancestor species may be lost.
All ecosystems are plant-based. Plants produce oxygen, making life on Earth possible, and perform a vital task for other life forms by absorbing vast amounts of toxins and carbon dioxide. They are the source of thousands of important medicines, and discoveries of new medicinal uses of plants are being made on a regular basis. Disappearance of individual species of plants can impoverish or even collapse entire ecosystems when they are key to the survival of many species of animals or form an intrinsic link in an ecosystem.
Not only do many plants fade to extinction undocumented by botanists, but only a small percentage of living plants have been scientifically described. Botanists have identified more than 250 thousand types of living plants other than algae, fungi and bacteria, but most scientists agree these represent perhaps a tenth of all living plants. Almost 10 percent of surviving species are considered threatened with extinction. Some 34 thousand plant species are listed in the 1997 IUCN Red List (Walter and Gillett 1998). Many of these plants have not been seen for years and may be declared extinct in the near future, or are clinging to life with only a few individuals left. Preservation of the planet's great diversity of plants to prevent further extinctions should be a priority of the first order.