feature
Going, Plant Species
Extinction in the 21st Century Prospects for halting it or even slowing its rate are bleak, but perhaps not hopeless. JULIAN
JOSEPHSON
1 3 0 A • MARCH 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
think that essentially all of the plants native to my islands, whose habitats are I along or near the coastline, are threatI ened," Arnoldo Santos-Guerra of the H Jardin de Aclimatacion de La Orotava (Tenerife, Canary Islands, Spain), observed. "Higher up, above La Palma [Canary Islands], I found one last specimen of a native plant species. I was able to get ripe seeds and reproduce it at the Botanical Garden. This only specimen was totally destroyed [in the wild] a few weeks later by animals introduced into the Caldera de Taburiente National Park in 1972.1 do n o t know how m a n y species [known a n d u n known] we could not save," he told a press conference at the XVI International Botanical Congress (IBC), which took place in St. Louis, Mo., in August. Santos-Guerra attributed this loss of plant species diversity largely to heavy land development; the Canary Islands are a popular tourist resort, especially in winter. Mindful of the species depletion reported from the Canary Islands and desiring to pre•
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Gone?
Pleurophyllum, a unique subantarctic island plant species.
serve native species on the Azores, the cognizant Portuguese authorities are instituting controls on coastal and upland development (i). Greg Anderson of the University of Connecticut and colleagues from Ohio, Argentina, Austria, and Chile warn that rates of species decline and extinction on islands indicate in microcosm what could be happening, and indeed is happening, on a macrocosmic scale. They have been studying and cataloging native plant and animal ecosystems on islands of the remote Juan Fernandez and Robinson Crusoe archipelagoes. (Administered by Chile, those relatively isolated islands are in the vast southeastern Pacific Ocean.) An example of near-extinction: On Robinson Crusoe Island, one of Anderson's colleagues found a botanical relative of the sunflower, which was appropriately named Robinsonia. This plant is dioecious (male and female flowers appear on separate plants, much like the sweet cherry). The scientist found the last surviving (male-flowering) specimen; by so doing, he may manage to keep the
individual alive, though without the corresponding female plant, the species will still likely go extinct. Thomas Givnish of the University of Wisconsin said that on Hawaii, he saw the last known individual of several species of Cyanea (a lobeliad, the largest plant genus endemic to Hawaii, which originally comprised more than 100 species). One of these died, and the species went extinct just a few months afterward. Anderson and colleagues noted that island plant ecosystems thrived and became highly specialized in remote environments such as the Juan Fernandez Archipelago—at least, before human settlement— because they had little or no competition. In one extreme case of specialization of a plant species he examined on Robinson Crusoe Island, "We saw no variation between the few individuals, even at the molecular level. Zero." Normally, same-species plants even in the same habitat show some molecular differences, even over small distances within the habitat. These could be brought about by variations in the mineral content of the soil and the amount of MARCH 1, 2000/ENVIRONMENTAL SCIENCE & TECHNOLOGY/NEWS " 1 3 1 A
sunlight and water received; these have become detectable, thanks to the sophisticated techniques of modern analytical molecular biology (see box on next page).
Lessons from the microcosm What lessons might be applied from observations of the attenuation and extinction of plant (and animal) species on islands—the microcosm—to living populations on the large land masses (the macrocosm)? Anderson observes that increasingly on continents, ecological "islands" are being formed through habitat destruction and fragmentation of larger ecosystems when these ecosystems are not eliminated entirely. Anderson gives as an example the American prairie lands on which very few native grassland ecosystems are left, because the bulk of these lands have been converted to extensive cultivation of grains and soybeans. The small, highly fragmented native prairie ecosystems that remain have become, in effect, "islands" that are far separated from each other in a "sea" of cultivated land and agricultural crops, and between which there is essentially no biological "communication", such as pollination from plants of the same species restricted to other such "islands". Having few or no opportunities for genetic renewal, plant species contained therein become genetically depleted, inbred, and weakened, and go into decline, and this decline eventually affects animal populations adversely. Analogous situations are occurring widely in forests, especially in the tropics, as more land is converted to agriculture and to industrial, residential, and resort development; and trees are being harvested unsustainably for lumber. Another factor in the decline of species diversity on islands and continents has been invasion of habitats by "exotic" or "foreign" species, a major problem.
Moreover, if ecosystems are getting smaller and being fragmented or essentially gutted, such portions of ecosystems that remain would be "unable to function," Raven explained. "You would lose many of the basic foods, animals, and other ingredients that keep the ecosystems going." Indeed, if human existence itself is not threatened by the wholesale loss of plant species, the quality of human life almost certainly will be sharply degraded. In addition, the loss of knowledge to science would be immense. Raven estimates that of 7 million to 10 million eukaryotic species on earth, about 300,000 species of plants plus 50,000 species of algae are photosynthetic, as are "a few hundred" species of (prokaryotic) bacteria. Of the estimated 300,000 species of plants worldwide, perhaps 250,000 species are known, which leaves about 50,000 yet to be discovered. More important, perhaps, of the total number of eukaryotes believed to be extant, science has cataloged only 1.6 million. This leaves a huge number of unknown species, most of which are in the tropics, according to Raven. If tropical rain forests are destroyed, he estimates that 19 of 20 species never will become known to science. One devastating effect could be the foreclosure of the future availability of many useful chemicals and medicaments.
Bleak, but not yet hopeless
Although prospects for the continuing loss of species are bleak, they are not yet hopeless, Raven believes. "In fact," he proposes, "the situation could be turned around in as little as three years if the political will [worldwide] is there. It should even be possible, in principle, to save all the species that are left in the world. This could be done," Raven suggests, "through the United Nations." He calls for organizing a comprehensive coordinating body that can look at n a t i o n a l a n d regional efforts Bleak outlook for 2100 throughout the world. The Internet Addressing the macrocosmic scale, would be used to track various spePeter Raven (see photo at right), dicies' abundance and status in narector of the Missouri Botanical Garture and find those most seriously dens and president of the IBC, keythreatened throughout the world. n o t e d the Congress with a bleak prognosis for the status of plant (and "For us to save the world's plant speconsequently, animal) biodiversity by cies," Raven adds, "we have to do an ex2100: "If no action is taken now, oneercise that is very difficult for us to do third of all plant species will be excomprehensively, which is to have the tinct or en route to extinction by the 20% of the world's people who have middle 2000s and two-thirds by 2100. about 85% of the world's money and This is about the proportion that bescientists pay for it 'a bit' and get tocame extinct 65 million years ago gether with the developing world to set (suddenly, at the close of the Meso- Raven: "Two-thirds of plant spe- up a system that will do [this task]. Bear cies could be gone by 2100." zoic Era]." in mind that developing countries have only about 15% of the world's money Raven continued, "Rates of extincand 15-20% of the world's scientists. Because of the imtion [currently] are hundreds of times what they had portance of plants, this initiative would be well worth been for the past 65 million years. We can chronicle that pushing very hard. In fact, it's difficult to see why no by noting the rates of disappearances of species of repone has gotten that rolling yet." Raven moved that the tiles, birds, and mammals over the last several hunIBC "pass a resolution calling for just such an initiadred years and comparing this rate with the fossil tive, and then we go on to a major coordinating conrecord. That rate is accelerating as ecosystems all over ference in which we say mat we're not going to stand the world are being fragmented and habitats are getfor it [continued gutting of ecosystems] any more." ting smaller." Raven quoted figures from a compreA concrete strategy will be formulated at a conferhensive analysis by Stuart Pimm of the University of ence to take place in Asheville, N.C., lune 25-30,2000. Tennessee (now at Columbia University) (2). 1 3 2 A • MARCH 1, 2000 / ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS
One factor that could aid plant species conservation is that "plants are a special situation", as Raven put it. When he analyzed figures compiled by Peter Wyse Jackson of the Botanic Gardens Conservation International (BGCI, Richmond, Surrey, United Kingdom), he found there could be 80,000 species in cultivation in botanical gardens. Perhaps 5000 more are in cultivation outside botanical gardens, for example, in parks and private gardens. "Because we can cultivate plants, we have a better chance of saving some of them than we do some other [organisms]," Raven explained, adding that such matters will be discussed at the forthcoming Asheville, N.C., conference, of which the BGCI is an organizer (www. rbgkew.org.uk/BGCI). Raven also noted the three principal factors that are accelerating the extinction of plant species: habitat destruction (the most significant factor); ecosystem fragmentation; and invasion of remaining ecosystems by nonnative species. With respect to habitat, "Obviously, the best way to save plants is to save real estate. If a rain forest is destroyed, 19 of 20 species there will remain unknown to science." If whole ecological communities are being wiped out, a "second-best" approach to species preservation "would be to reintroduce them in nature. But that is meaningless unless you can reconstitute [ecological] communities in which the species can function." As a "third-best" strategy, if communities cannot be reconstituted, "we would rather have germ plasm [from those species that remain] than not have the species at all." Raven added, "Because of the special nature of plants, we can still preserve many and still have them in existence [even if they are extinct in nature]." Plant tissue might be preserved much like animal tissue is in the frozen zoo part of the San Diego Zoological Society's Center for Research on Endangered Species (CRES), where several hundred animal species are in tissue culture, and from which embryos can be reconstituted. "The [major] problem, however, will be to keep enough genetic variability around to reconstitute ecosystems." For this and many other reasons, Raven sees biodiversity preservation as "a major industry of the 21st century, [which] will be restoration ecology. It would involve rebuilding ecosystems around the world and learning how that can be done. For this, we need lots of biodiversity. Merely keeping species around [in repositories, haphazardly] is not enough, and it would be very hard to reconstitute a rain forest." For instance, trying to reconstitute a rain forest in northern Argentina versus one in the hotter climates of Brazil would require markedly different methods of choosing the species to reintroduce and then reconstructing their habitats and ecosystems.
"Cannot afford another decade . . ." A global strategy to arrest or at least reduce sharply the alarming rate of plant species extinction is part of the mission of the Species Survival Commission (SSC), a unit of the International Union for the Conservation of Nature (www.iucn.org). In existence for 50 years, the commission is made up of a network of 7000 volun-
Why extinction is so common on islands Species extinction is thought to be common on islands because plant and animal populations already constrained by the island's area were initially so small, because humans can directly destroy so great a range of the natural habitats, because so many island species have evolved in situ and are found nowhere else on earth; and because their evolution in isolation has made them particularly sensitive to introduced competitors, herbivores, and predators. Thousands of bird species evolved flightlessness on islands, filling ecological roles equivalent to those played by poorly dispersing mammals on continents; almost all of these were driven extinct when human hunters and their associated rats, cats, dogs, and livestock arrived on islands throughout the Pacific and Indian Oceans. Hundreds of plant species have become endangered or extinct in the Hawaiian Islands alone after pigs, goats, deer, pronghorn, and cattle were introduced, where plants had evolved without having to defend themselves against mammalian herbivores. Exotic plants have greatly changed the fire regime, or soil chemistry, or intensity of shading in many island habitats, endangering many other plants and the animals that depend on them. Cyanea alone had numerous animal species dependent on it: fruit flies that mated or laid their eggs on individual species, tree snails that grazed on its leaves, nitidulid beetles that lived in its flowers, and native birds that pollinated its flowers or dispersed its fruits. Islands are microcosms that show how outright habitat destruction, habitat fragmentation, and invasion by exotic species can lead to high rates of extinction. We have already seen how much damage has occurred on tropical oceanic islands, and this observation provides an important basis for predicting how habitat destruction, fragmentation, and exotic species will cause loss of biodiversity on continents as well. To try to save some critically endangered plant species, the U.S. National Tropical Botanical Garden has taken the lead in gathering seeds from the few remaining individuals of several critically endangered species and putting them into cultivation. Some scientists have scaled cliffs and extremely steep slopes across the islands, seeking the few individuals that have escaped the depredations of pigs, goats, cattle, and axis deer—and in the process, rediscovering a number of species thought to be extinct. Researchers at the Lyon Arboretum outside Honolulu have been able to propagate several exceedingly rare species using tissue culture, an essential approach in instances in which only one individual remains in the wild and may not be able to self-pollinate and set fruit.
teer scientists and conservation professionals worldwide. SSC Chair David Brackett, who also is the directorgeneral of the Canadian Wildlife Service, emphatically agrees with Raven that "We live in one of the most expensive decades of the most expensive century in history, when measured in terms of the loss of the unique diversity of life on this planet. It is at least 1000 times the background extinction rate. Decreasing the rate of loss of species is the mission statement of the SSC. We cannot afford another decade, let alone another century of loss." The commission listed a number of concrete steps that it plans to take to help reduce the rate of species extinction (3, 4) (see box on next page). Among 250 priority "hot spots" ("places of particular concentrations of species richness," as the SSC defines MARCH 1, 2000/ENVIRONMENTAL SCIENCE & TECHNOLOGY/ NEWS • 1 3 3 A
Some conservation steps proposed by the SSC As part of the new initiative, experts within the Species Survival Commission Plant Program have set forth conditions that must be met to ensure the survival of threatened, endangered, and economically or otherwise important plant species. • Sound scientific information must underpin decisions and policies affecting plant diversity. • Activities should immediately focus on biological "hot spots", particularly those that are under pressure from human influences. • Rigorous criteria for identifying, classifying, and prioritizing sites of high plant diversity must be developed, shared, and used to determine where best to place resources. • Information-gathering programs must be created and coordinated in those regions rich in plants with economic or social values. • Effects of invasive plants and animals, major sources of species depletion, must be reduced. • Sustainable use of plant species must be promoted, taking the needs of resource users into account and working within the spirit and the letter of the Convention on Biological Diversity. • "Best practice" manuals, focusing on conservation management in key biodiversity areas, must be developed, and local people (those who actually do conservation) encouraged to practice integrated conservation action. • Solutions must be long-term and include international- and nationallevel plant conservation training programs, particularly for nations with few scientific and financial resources. These proposals are very ambitious, but necessary. "We've set high goals for ourselves and for our partners," said Dr. Given. "But they are high out of necessity. The fate of plant species, and ultimately the health of the planet, rests in our abilities to achieve these goals. We can do so only if we can build on the concerns and actions of individuals and institutions around the world."
Given added, "There is never enough money, of course. A rough estimate is that $10 million-$12 million a year could at least alleviate some of the problems." Quoting from New Zealand newspaper accounts, Given alluded to a work of art that sold for $12 million. "We could have bought a 12 millionyear-old wetland in New Zealand with unique species for this sum; that's a dollar a year. One dollar a year for the plants' evolution, yet someone pays $12 million for one work of art! In a biological sense, the wetland is an equivalent unique work of art."
Species versus hotels
them) are the islands of Madagascar and New Caledonia, the dry lands of Somalia, forests of northern Borneo (i.e., Sarawak and Sabah), and the Edwards Plateau in West Texas. "We cannot afford to compromise these types of places," said David Given of the International Centre for Nature Conservation at Lincoln University (Christchurch, New Zealand), chair of the SSC's Plant Program. Additional efforts would include the expansion of national parks, botanic gardens, seed and gene banks, and international conservation biology research and education. Perhaps one of the most important initiatives would be the preservation of wild species that are relatives of major crops.
Brackett and Given were asked: "What happens when 'interventionists' [such as the SSC] come up against large companies that seek to construct large hotel or time-share building developments, such as those seen at resorts on the Canary Islands and other climatefavored parts of the world? Maybe the value of the conserved plants ultimately is high, but that could be commercialized 20-30 years in the future at best; a bottom line-oriented businessman would regard this potential value as 'pie in the sky' and a lot of guesswork. A developer might say, 'We can get a hotel complex up in three years and get our money out fast, maybe in three years.' How does one argue with that commercial viewpoint? The notion that a company can take the profit in three years, but, as Mr. Brackett observed, can't replace the species that are gone forever likely will fail to impress most developers, agribusinesses, and logging companies." Brackett and Given said that in many cases, governments might have to intervene to slow down commercially driven ecosystem destruction. On the other hand, Given gave an example of how species conservation pays fast: During the 1960s, a potentially catastrophic epidemic of virus disease of rice broke out in Southeast Asia. A search of seed and gene banks found a single sample of an immune type of rice in the wild, near Bangalore, India. Only 12 seeds of this type of rice, with the right genetic material, were available anywhere in the world. This genetic material from those 12 seeds was then bred into all of the varieties of rice in Southeast Asia. "So how much were those 12 seeds worth monetarily if they stopped a killer crop epidemic?" Given asked. "It must be reckoned in many tens of millions of dollars! This is not a future value, but a big current value. Who knows how often this situation repeats itself?"
Cost estimates for conservation
Needed: A botanical "giant panda"
What level of funding would be needed for conservation efforts of the magnitude envisioned by the SSC? Brackett acknowledged, "We don't know for sure. Because much of our work is done by a volunteer network, we don't operate on a budget like governments do. I could answer for Canadian Wildlife Service, but I can't speak for SSC because how do you value the time of volunteers or host institution support? But I can estimate that the plant portion would have as many as 1000 people working around the world. We can be sure that the effort will represent a huge investment. An initial estimate of the total amount needed may be $20 million a year."
Brackett and Given agree that it is necessary to develop incentives to conserve plant species, such as opportunities for bioprospecting for chemicals and medicines. But such long-term projects will long outlast the public's attention span. "The public consciousness needs to be raised with a 'giant panda' of the plant world," suggested Bill Allen, a science writer for the St. Louis Post-Dispatch. "What plant is the equivalent of cute and cuddly like a panda?" Although it is difficult to conceive of plants as "cute and cuddly", Given offered two examples. One is Pleurophyllum, a tall, spectacular species of purpleflowered daisy that grows on subantarctic islands such
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as the Aucklands, the Snares, Macquarie, and Campbell in the "roaring forties and furious fifties" of south latitude (see photo on pages 124A-125A). The plant sometimes attains a height of 1 m, despite the harsh climate. Given has become an advocate for such plants through the "ecotours" that he leads to those islands. Another is the bizarre Rafflesia blossom, which often is 1 m in diameter, and is the world's largest flower. When it matures, it gives off an odor redolent of spoiled meat. Its habitat is in rain forests in Southeast Asia, especially Sarawak, a state in Malaysia. Malaysian authorities put out "Rafflesia notices" to advise tourists when it is possible to see them in bloom.
Pangaea all over again! A major threat to biodiversity is the incursion into ecosystems by invasive species, which may be nearly as destructive as h u m a n activity. In fact, most of these incursions have come about as a result of human activity, mainly through expanded sea and air transportation and settlement. In some cases, "foreign" species migrated to new habitats through accident or human carelessness, but often, such migration was brought about deliberately, often for commercial purposes. An early example of destructive effects is the decimation of the extensive stands of the prized American chestnut {Castanea dentata), by a blight fungus accidentally imported in 1904 via Asian chestnut trees shipped to the United States as cultivars (4). Currently, almost no mature American chestnut trees exist. In years and centuries past, biogeographical boundaries, mainly in the form of broad expanses of ocean and high, massive mountain ranges, inhibited these invasions. "International commerce by sea and air has been the principal factor in breaking these boundaries down; it's Pangaea all over again," remarked Harold Mooney of Stanford University at a technical session of the IBC. Mooney was referring to a time during earth's geological history, perhaps 240 million years ago (4), when, supposedly, there was one massive continent and the rest of the planet was ocean. "In Hawaii today, for instance, there are as many invasive species as natives," Mooney observed. "The same will soon be true in the Galapagos Islands. Many of the invasives there are doing great damage. Cinchona (quinine) plants that have escaped cultivation are taking over native forests." On Santa Cruz Island, blackberries, imported for their fruits, are now crowding out endemic Scalesia ("tree daisy") and other native species. Ecuadorian authorities have started a project to uproot the blackberries in the hope that the native species can recover (5). Invasive species not only fragment plant and animal habitats. They also alter the water, nutrient, and fire cycles, Mooney pointed out. They even affect atmospheric composition and nitrogen deposition. Moreover, they do economic damage. David Pimentel of Cornell University estimates that in the United States alone, their current cost—this is not a misprint—is $138 billion a year (6).
Conventional wisdom has it that invasives do well in a new habitat because they leave their natural enemies behind. Perhaps, but do they thrive also because they find "friends"? For example, honeybees help pollinate invasive and native plants. In California, John Randall of The Nature Conservancy, with other scientists, tried tying small bags over flowers of the yellowstar thistle, an invader from Europe. Honeybees could not pollinate the flowers, and seed production decreased by about 50% (7). Could steps such as these and other measures that interfere with the life cycles of invasive species (along with introduction of natural enemies and efforts for outright eradication) help curb their spread? Serious attempts to control invasive species are being made in the United States, Australia, and, especially, South Africa, where eradication teams are being sent out into the field. Mooney remains pessimistic about the outcome: "The rate of invasion is now high, and chances of total reversibility are slim."
The role of taxonomy The science of plant taxonomy could boost conservation efforts, said Brent Mishler of the University of California-Berkeley's Jepson Herbaria. This discipline has evolved substantially during the past 15 years and could add much to botanists' knowledge of just what is being conserved and what needs to be conserved. The main contributor to advances in taxonomy has been the increasing sophistication of genetic mapping, molecular biology, and analytical chemistry. One prime example of how advanced taxonomy encourages conservation is the discovery of Amborella on the island of New Caledonia; it was "hiding out" there, as Mishler put it. Through DNA and molecular biology studies, Amborella has come to be regarded as closely related to the common ancestor of all flowering plants. Another striking finding is that the protozoan Plasmodium, which causes malaria, has vestigial plastids, which bespeaks plant ancestry (8). Improved knowledge of taxonomy, Mishler suggested, could be a key to preserving DNA with a view to restoring moribund and extinct species in the future. He acknowledged that restoring extinct organisms with saved DNA is an extremely remote possibility, but, as he speculated, "Who knows what future know-how and knowledge might make possible?"
References (1) Indice acores. www.indice-acores.com (accessed Nov. 1999). (2) Pimm, S. L. Science 1995, 269 (5222), 347-350. (3) Bracket!, D.; Given, D. R. Presented at the XVI International Botanical Congress, St. Louis, Mo., Aug. 1999. (4) Bright, C. LifeoutofBounds;W.W. Norton: New York, 1998. (5) News items from Galapagos Conservation Trust, www. gct.org/news.html (accessed Nov. 1999). (6) Pimentel, D., BioScience, in press. (7) Duris, B. Nature Conservancy 1999, 49 (7), 7. (8) Mishler, B. Presented at the XVI International Botanical congress, St. Louis, Mo., Aug. 1999.
Julian Josephson is a freelance science writer and former associate editor of ES&T, residing in Bethesda, Md. MARCH 1,2000/ENVIRONMENTAL SCIENCE & TECHNOLOGY / NEWS • 1 3 5 A
