Plant Conservation in the Flora of North America Region

George Yatskievych

Richard W. Spellenberg

SETTLERS from Europe who began the modern colonization of North America in the sixteenth century brought rapid changes to the landscape of the continent. The natural biological systems of the lands from which these colonists originated had already sustained massive alterations. By that time, many tracts of European forests had been lumbered for fuelwood or cleared for farming, a trend dating back to the Greek and Roman periods and earlier (J. Perlin 1989; A.S. Mather 1990). Food chains had been altered by overhunting of game species and extirpation of top predators. Large areas had suffered from overgrazing by domestic animals, and erosion was a widespread problem, especially in southern Europe. Various types of pollution were also affecting the environment around settled areas. As colonists from the Old World arrived in North America and moved westward, they naturally implemented the land ethics of their forefathers, resulting in the gradual degradation of many natural habitats and their constituent plants and animals.

It was not until the latter half of the nineteenth century that the American conservation movement gained momentum. The nature writings of Henry David Thoreau in the mid-1800s did much to sensitize readers to the wonders of the outdoors. His writings influenced the later works of John Muir and others, which had a more direct effect in stimulating conservation in the United States (S. Fox 1981). The first state plant protection law was passed in Connecticut, in 1869, to protect dwindling populations of Lygodium palmatum (Hartford fern, Schizaeaceae) from overcollection for horticultural purposes (W. D. Countryman 1977). Although no longer in effect, this law set a precedent for future rare plant legislation in North America. At about the same time, in 1872, the world's first national park was established at Yellowstone in the Rocky Mountains, now a part of an extensive system of parks throughout North America (fig. 10.1). Banff National Park, the first in the Canadian system, was established in 1885 (M. Finkelstein 1990).

Today, conservation is a familiar topic. North Americans are inundated with daily reminders to recycle waste materials and conserve resources. The news media are filled with reports on deforestation, pollution, global warming, endangered species, and other environmental issues. Review literature is beginning to summarize the issues (e.g., G. Lean et al. 1990). Conservation organizations are ever more active in soliciting membership and involvement from the public and in raising funds to address specific issues in nature. Much of the public's attention has been focused on critical concerns in the tropics, but the loss of biodiversity in the temperate zone is every bit as important and timely. In the continental United States alone, an estimated 90 species of vascular plants have become extinct during the past 200 years, and many additional species are in imminent danger of extinction (E. S. Ayensu and R. A. DeFilipps 1978).

Plant conservation in North America is best treated as a series of interrelated topics. These include a general rationale for preserving biodiversity, a discussion of problems in preserving individual species and their habitats, some definitions for terms describing species rarity, a summary of private and governmental contributions to plant conservation, and notes on present and future challenges. Some aspects of these topics are considered below.

The Importance of Conserving Biodiversity

Even with increasing attention given to environmental problems, the public in general is mostly unaware of the magnitude of the impact by humans on the environment, of the negative aspects of this often irreparable damage, and of its effects on the quality of life. A vivid general review of the multifaceted nature of the human assault on the natural world is presented in G.Lean et al. (1990). The value of biodiversity in economic terms remains questionable for most people when it is considered, for example, that the extinction of at least 90 plant species since 1800 in the United States seems to have had no negative effect (J. M. Moran et al. 1986).

A number of excellent reasons exist for preserving the organisms that share the planet with humankind. Most people actually involved with conservation of natural resources will cite moral and aesthetic criteria as principal reasons for preserving biodiversity (B. G. Norton 1986b). Other important arguments can be made to justify this need. The four main lines of reasoning in regard to preservation of biodiversity include: ethical and moral obligations, aesthetic and recreational potential, ecological impact, and economic impact (J. T. Miller 1985; Smithsonian Institution 1975). The last two topics, in particular, are inextricably related to one another.

Ethical and Moral Obligations

This argument is difficult to defend because of the widespread perception of a need to "develop" the natural world constantly for the immediate gain of humankind. It states that the extinction of any species diminishes the environment in both real and intangible ways and, from a moral standpoint, diminishes the human race, which is responsible for the welfare of every species. The concept that species have some sort of intrinsic value, and not only instrumental value, as discussed by J. B. Callicot (1986), has been rejected by many individuals, who retain a deep-seated belief that the natural world was created only to serve humankind. In contrast, others hold the view that humankind, as a species of thought and conscience, has a moral obligation for rational stewardship of nature. As Callicot discusses, doubts about the ethical-moral position very likely derive from the Judeo-Christian tradition, which gives humanity dominion over Creation and simultaneously believes that Adam was to "dress the garden and keep it."

Aesthetic and Recreational Potential

This line of reasoning is well understood by those who treasure time spent in the wild, but less so by individuals concerned more with economic interests. Diversity in nature and the presence of unspoiled places are crucial to humankind's general view of its place in the world and more specifically to the well-being of individuals. For many individuals, wild places provide a needed psychological refugium from the pressures of the civilized world.

Ecological Impact

This rationale is particularly associated with the economic argument and also not fully separable from the aesthetic-recreational rationale for the preservation of diversity. It is the least well understood by most nonbiologists. For this line of reasoning to be effective, the value of maintaining complexity in ecosystems must be defined as an economic and political issue. Local extinctions may be viewed as indicators of the declining health of natural communities and the reduced potential of these communities to provide free services to humankind.

Societies are generally unaware that most of the energy used by humans flows through giant, complex, little understood systems of natural communities, not through technology and agriculture (G.M. Woodwell 1977). Humans, as one species among millions globally, appropriate a disproportionately large amount (up to 40%) of the net primary productivity of terrestrial ecosystems (P.M. Vitousek et al. 1986). In these ecosystems, the loss of a single organism may affect the interactive controls on population levels of other organisms in the system, especially if the extirpated organism occupies a high place in the food chain or is a dominant member of the plant community (G.J. Vermeij 1986). At the local level, the simplification of a community may mean a reduction in productivity, a portion of which might be harvested directly by humankind, as in native grasslands or forests. Healthy, functioning ecosystems provide countless free services (P.R. Ehrlich 1980), which include climate regulation, waste disposal, and regulation of air and water quality.

Many scientists hold the view that extreme simplification of inherently stable, complex systems results in growing ecological instability and a reduction in the ability of these systems to withstand extreme environmental conditions, whether physical or biological in nature. This has been called the "diversity-stability hypothesis" (B.G. Norton 1987). Not all environments contain equal biotic complexity, and some evidence exists that this line of reasoning is not always applicable (B.G. Norton 1987). There are strong correlations, however, among complexity of an ecosystem, species diversity in that system, and the number of taxa in the system that are likely to become imperiled from any environmental perturbations. Moreover, evidence indicates that once extirpated from a particular site, species tend to be replaced by different taxa, and the ecosystem tends to become permanently altered (G.M. Woodwell 1977; B.G. Norton 1987). Thus, whether or not one accepts the diversity-stability hypothesis, the simplification of complex environments is clearly a detrimental phenomenon.

In a concept titled the "environmental trigger," G.Lean et al. (1990, p. 109) point out that environmental degradation, such as deforestation or desertification, makes some environmental disasters worse, and may trigger others. Unquestionably, in direct economic terms a biologically simpler world will become ever more expensive to maintain. Humanity must make the choice in the next decade either to continue as usual or to work effectively to maintain complex ecosystems and biological diversity; that is, to face squarely the environmental question. This choice will result in either a continuingly rich or an increasingly impoverished existence (T.E. Lovejoy 1980, 1986; G.Lean et al. 1990). The loss of a single species may seem insignificant, but when threatened species are taken as a whole, they indicate a severely stressed environment (T.E. Lovejoy 1979) and portend ecological problems of increasing severity.

Economic Impact

This rationale has been most usefully applied when there has been resistance to using public revenues for the protection of plants and animals that seemingly have no direct material value. Wealthy, highly developed countries can more easily afford protection of biodiversity than can developing countries, where much of the populace lives at subsistence level. These less developed countries must first provide opportunities for their citizens that do not require immediate exploitation of easily utilized resources.

Central to the economic argument, according to M.L. Oldfield (1984), is that "genetic resources from wild species and primitive forms of domesticated plants and animals provide the biotic raw materials that underpin every major type of economic endeavor at its most fundamental level." Once lost, a species can no longer benefit humans. In addition to presently utilized resources, extensive biodiversity provides humankind with the opportunity to discover new foods, fibers, drugs, plants for horticultural use and land reclamation, and so on.

Wild relatives of crop plants are important for the improvement of domesticates through research programs by plant breeders. The maintenance of diverse gene pools in other wild plants is taking on new importance in pest management and for the development of new agricultural crops, as the ability to move genes between species becomes feasible by modern methods of genetic engineering. The study of plant species provides information of direct economic value or of indirect use in the solution of numerous biological problems. The preservation of species as data sources for future research may be one of the most important contributions that can be made by biologists today (T.E. Lovejoy 1979). It now borders on cliché, but to lose species before they are studied for their biochemistry, physiology, evolutionary relationships, and ecology is tantamount to tearing pages from a book before it is read.

A variety of North American plants provide examples where native species individually are, or may be at a later time, commercially exploitable. Uses of these plants range from horticultural to medicinal and include such categories as plantings for erosion control (several families) and waste water filtration (several families), alternative crops for human foods (e.g., Zizania species, wild-rice, Poaceae) or animal fodder (e.g., Cucurbita foetidissima, buffalo gourd, Cucurbitaceae), and plants cultivated for unusual chemical constituents, such as the liquid wax found in seeds of jojoba (Simmondsia chinensis, Simmondsiaceae).

The number of North American species used in outdoor plantings has grown in recent years, as garden clubs, native plant societies, and nurseries have sensitized the public to the aesthetic and economic advantages of well-adapted, low maintenance alternatives to traditional garden plants. Successful use of native plants has increased public awareness, reducing the perception of the "weediness" of native species in the garden setting and reinforcing their desirability. Widespread acceptance of many species by the nursery industry as a whole was at first fairly slow but is now increasing. The establishment of native wildflower nurseries in many states (National Wildflower Research Center 1992) has helped to create a viable market, thereby making the widespread cultivation of several species by larger business concerns economically attractive.

Some plant types, such as drought-resistant species, plants native to prairies, and species that attract wildlife, have become particularly popular in various regions. In the Southwest, for example, "Xeriscaping" (the use of drought-tolerant, native plants for landscaping) has been effective, for it requires little maintenance and depends on natural rainfall, thereby conserving the limited water supplies (C. Ellefson et al. 1992). This has not been without its problems, however, as some native plant populations, especially those of cacti and yuccas, have suffered severe declines following removal of plants by unscrupulous collectors for transplanting to yards. Presently, however, laws and conservation education are reducing horticultural predation on native plant populations, and an increasing number of commercial plant growers are investing the time and resources necessary to grow such plants from seeds or other propagules. In a few situations, regional endemics such as Washingtonia filifera (desert fan palm, Arecaceae) are actually more common in cultivation than in the wild.

A large number of plants also have potentially useful medicinal properties. Although plants have provided chemical compounds for use in numerous medicines, the majority of species have never been tested for potential medicinal, antifungal, or antibiotic properties. Even with several private and federal projects currently underway to test samples of large numbers of species, a long time will elapse before a significant percentage of the North American flora has been screened even cursorily by biochemists.

Success stories regarding the discovery of economically valuable, medicinal compounds among North American plants are not difficult to find. Taxus brevifolia(Pacific yew, Taxaceae), a small understory tree endemic to old-growth forests in the Pacific Northwest, provides an example of a species threatened by several factors, including its value for unusual chemicals. Although trees are too small for commercial lumber, they are damaged directly by logging operations that remove other commercially valuable conifers around them. The remaining yews become less vigorous after the shade-providing canopy of old growth is gone. In addition, yew wood is dense and red, making it desirable for fine wood crafts, and these slow-growing trees are often removed for this purpose. Recently, the National Cancer Institute's plant screening program discovered that an extract from the bark of this species yields the terpenoid taxol, which has been shown to be effective in the treatment of some kinds of cancer (D.Hinkley 1990).

The use of Taxus brevifolia in medicine, however, is not without problems. Biochemists have been unable to synthesize taxol successfully, so availability of the compound still depends on the extraction of plant materials from Pacific yew and some other Taxus species known to possess lower concentrations of taxol in their tissues. The harvest of bark from the plants, resulting in death for the plants and a relatively low yield of taxol, coupled with the need for large quantities of the compound for clinical trials, has alarmed some conservationists. During 1987--1990, as many as 62,000 mature specimens of Pacific yew were harvested for the National Cancer Institute (D.Hinkley 1990). This process yielded taxol in quantities sufficient only for short-term clinical tests. The remaining natural populations of this slow-growing species clearly could never sustain the level of collection necessary if taxol gains federal approval as a cancer treatment, and the future of this compound in medicine may ultimately depend on large-scale cultivation efforts.

Preserving Species and Habitats

Extinction is theoretically the ultimate fate for all species and, in that respect, it is a natural part of ecological and evolutionary processes. The world is now in peril, however, of entering into an extinction event of great magnitude (P.R. Ehrlich 1986; D.Simberloff 1986; N.Myers 1987; P.H. Raven 1987; E.O. Wilson 1988b). Extinction rates are estimated today to be 40 to 400 times greater than those that occurred in the past. By the year 2000, at least two-thirds of the tropical forests may be gone, and up to one million of the species that presently inhabit the earth may have perished (T.E. Lovejoy 1980, 1986), most of them totally unknown to science.

P.H. Raven (1987) has estimated that plant extinctions may be occurring presently at the rate of one or two species per day, and that during the next two to three decades global extinction rates for plants may average about 2000 species annually. Massive extinction events mark the ends of the Ordovician, Permian, Triassic, and Cretaceous periods, but at these geologically abrupt transitions, groups that underwent extinction were replaced by other newly evolving organisms. Now, with human-induced degradation of the environment, the same magnitude of change that accompanied these earlier extinction events is occurring again, but in a matter of a few centuries, rather than over many thousands of years. New groups of species are not able to evolve quickly enough to replace the old, and an unprecedented loss of biodiversity is permanently altering the course of evolution.

Although levels of plant extinction are of lesser magnitude in temperate regions than in tropical forests, which contain 50% (N.Myers 1980; E.O. Wilson 1988b) to 90% (T.L. Erwin 1983, 1988) of all species of organisms, the threats to species of North American flora are still a topic of great concern. As is illustrated by appendix 10.1, many different kinds of plants are affected by human impact on the environment. No particular class of life form seems to merit exemption. Understandably, regional endemics are most sensitive to environmental impacts, particularly when they occur in and near areas of urban development, as along the eastern seaboard and the West Coast.

Estimates by T.S. Elias (1977) and G.W. Argus (1977), among others, indicate that approximately 10% of the floras of the United States and Canada are endangered and rare, respectively. Elias further suggested that extinction rates in the United States increased during the period of 1800--1950. As noted earlier, about 90 plant species became extinct in North America during that time. A more recent survey suggests that as many as 475 additional continental United States taxa may become extinct by the year 1998 (L.Roberts 1988; Center for Plant Conservation, pers. comm.). As compared with the 1800--1950 period, that would be five times as many extinctions in one-third the length of time.

There are many reasons why species become imperiled in nature, aside from natural causes. All too often, complete and irreversible obliteration of habitat results from activities with direct economic purpose, such as inundation because of large dams, loss of habitat by urban expansion, and so forth. Reductions in diversity and in the health of habitats also commonly occur with more diffuse economic activities, such as ranching and logging, which often create a disturbance that allows other nonnative or "weedy" species to become established and spread. Highly focused (genus- or species-specific) activities imperil the existence of many species, as with excessive commercial and personal collecting for horticultural purposes, most notably among cacti and other succulents, orchids, and carnivorous plants (N.T. Marshall 1993). Some nursery catalogs continue to include offers of field-collected plants, although some of these species are protected by state law where they are collected. Ironically, many customers report high mortality rates among field-collected plants in their gardens and homes.

A related problem involves the overcollection of various native plants for the herbal trade. A number of unrelated species, such as Hydrastis canadensis (golden-seal, Ranunculaceae) and Echinacea species (coneflowers, Asteraceae), are collected in large quantities, usually by local "diggers," who sell their plants to regional dealers for processing and subsequent resale domestically or abroad. Although few of the most desirable taxa are uncommon enough to warrant federal listing (see below), the insatiable demand for herbal remedies, both in the Flora of North America region and around the world, has resulted in regional declines in population size and number for several species.

The best-studied example of this phenomenon is Panax quinquefolius (American ginseng, Araliaceae), which is presently a candidate for federal protection in the United States as an endangered or threatened species, and which has been treated as threatened in Canada in a Committee on the Status of Endangered Wildlife in Canada (COSEWIC) status report (D.J. White 1987). International trade in this species is regulated by virtue of its inclusion in appendix II of the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES; see below). The genus Panax has a long history of use in herbal remedies, particularly in Asia. By the early eighteenth century, P. quinquefolius was already being harvested for export to China by colonists and American Indians in both southern Canada and the northeastern United States (A.W. Carlson 1986). The high demand for wild-collected plants has not diminished since that time.

Efforts at commercial cultivation of the plant date to the mid-nineteenth century, but so far they have not kept pace with demand. According to Carlson, over 340,900 kg (750,000 lb) of wild ginseng were exported from the United States in 1822, which amounts to an estimated 18--22 million plants harvested from natural populations during that year alone. The total number of ginseng specimens removed from natural populations during the past 250 years staggers the imagination, and regional decline or extirpation has been reported in many parts of the range of the species (W.K. Smith 1988). Current laws mandate monitoring of harvest and sales by the individual states, but no comprehensive and detailed studies have been undertaken to correlate relative degrees of impact on the species as a whole with local levels of exploitation. Available biological evidence would suggests that further exploitation of wild ginseng should be halted in at least some portions of its range, but economic pressures have delayed actions to conserve this species properly.

Ultimately, however, the fate of most species in nature is tied to the health of the habitats in which they live. Most conservationists feel strongly that preservation of endangered species can only be brought about through effective conservation of ecosystems (G.T. Prance 1977; B.G. Norton 1986b, 1987). G.M. Woodwell (1977) noted that many earlier studies indicated a predictable pattern of shifting species arrays following disturbance in ecosystems. Disturbance-sensitive species, usually habitat specialists with high fidelity to a particular undisturbed community type, are extirpated or reduced in abundance, followed by rapid invasion of "weedy" taxa. Once established, the newcomers may be difficult or impossible to displace, and the original habitat often is, at best, difficult to reconstruct. Thus, preservation of natural ecosystems is essential to the conservation of overall biodiversity, as well as to the long-term survival of many individual species. Preservation of entire sites can be more efficient and cost-effective than attempting to deal with individual species on a one-by-one basis.

Habitats that are not unique or especially scenic, however, may be very difficult to preserve. In this respect, protection of individual species of plants has been valuable, for to preserve a species requires habitat preservation. Often several other species that may be in decline, but that are not yet threatened with extinction, are also given protection in this way. Thus, many of the governmental and private organizations engaged in conservation issues have focused on this approach, preserving habitat for a suite of species, for both economic and biological reasons (see below).

In the long term, however, the maintenance of species diversity must be achieved by the preservation of sufficiently diverse habitats of adequate size to ensure the persistence of complex, interacting communities. Toward this end, botanical gardens have developed an increasingly important role in educating the public on the importance of habitat preservation, and in studying the causes that contribute to rareness, endemism, and population decline. Among these important contributions is the feasibility of preserving plant species in gardens and seed banks in the face of unavoidable habitat loss. Such programs of preservation, however, should be viewed as short-term measures. When species are brought into gardens or seed banks for preservation, attempts must be made to retain samples containing sufficient genetic diversity to permit the eventual reestablishment of vigorous populations with long-term viability, when suitable habitat is again available in the wild (D. A. Falk and K. E. Holsinger 1991). These programs form a crucially important bridge between habitat destruction, potential extinction, and eventual species recovery.

In most of North America, a large proportion of the environment has been compromised by urbanization, extraction of commercial timber species from forests, plowing of prairies, grazing of rangelands, draining of wetlands, pollution, and related causes. J.M. Klopatek et al. (1979) examined the natural vegetation potentially remaining in the conterminous United States at the level of individual counties (fig. 10.2). Their analysis stressed how little natural vegetation remains in much of the eastern half of the country, particularly in the central states.

In states such as Iowa, Illinois, and Indiana, over half of the counties surveyed had less than 20% remaining potential natural vegetation. The situation is somewhat better in Canada (except in the prairie region), which has fewer people and a greater proportion of relatively intact vegetation, but areas of the country adjacent to its border with the United States have sustained large amounts of habitat destruction, particularly around the Great Lakes (G.W. Argus and K.M. Pryer 1990). Much of Greenland lacks vegetation because of permanent ice, but in those areas supporting plants, significant portions of the original vegetation remain intact, and human population density is generally low.

Very little is known about the life history, phenology, or autoecology of most plants, and our perceptions of species interrelationships in an ecosystem often result from hindsight after some taxa are diminished in abundance. The effects of various levels of disturbance of different kinds, including such seemingly innocuous aspects as the introduction of foreign pollinators, are usually not predictable based on currently available understanding. For example, the decline of the American bison in the nineteenth century and the general depletion of large game mammals in the eastern half of the United States by the early twentieth century are well-known facts, but the correlation between mammalian depletions and the concurrent decline of a native plant species, Trifolium stoloniferum (running buffalo clover, Fabaceae), has only recently been appreciated (R.E. Brooks 1983). This clover, which once grew from Kansas to West Virginia, apparently was dependent on large mammals both for seed dispersal and for the creation of lightly disturbed microhabitats necessary for its establishment and survival (J.J.N. Campbell et al. 1988). Although populations of such herbivores as deer have recovered dramatically, Trifolium stoloniferum has only recently been rediscovered at a handful of widely scattered populations in its former range.

Invasive foreign taxa can also pose serious threats to the integrity of some habitats and their constituent species. Introduced species are a large component of the floristic diversity in most of North America. For instance, T.S. Elias (1977) estimated that 22% of the species found in the northeastern United States are exotics. Examples of the often rapid spread of "weedy" invaders, such as Salsola species (Russian-thistle, Chenopodiaceae), Alliaria petiolata (garlic mustard, Brassicaceae), and Tamarix (saltcedar, Tamaricaceae), are common. Once established in a community, exotic taxa can permanently alter it. They also may exert a selective influence on nearby communities as their seeds repeatedly and persistently compete for establishment there.

One of the best studied and most detrimental cases of habitat alteration by an exotic is that of Lythrum salicaria (purple loosestrife, Lythraceae). This Eurasian wetland species was introduced in the eastern United States in the early nineteenth century, probably as an ornamental and also by way of seeds from ship ballast (D.Q. Thompson et al. 1987). It rapidly spread westward in the United States and Canada, reaching the West Coast by the 1930s. Particularly since 1940, the species has become abundant in North American wetlands (D.Q. Thompson et al. 1987), forming dense stands to the exclusion of native species, including such widespread dominant and tenacious plants as Typha (cattail, Typhaceae).

This destructive species can invade relatively undisturbed sites, displacing all other plants but providing little in the way of resources for wildlife that live in, or migrate through, these wetlands. It undoubtedly also has contributed to the decline of many less common aquatic plant species, although no quantitative study has been published on this topic. In recent years, Lythrum salicaria has been declared a noxious weed in several states, with laws banning its importation and cultivation, and providing measures for its control.

Comments on Terminology

The vocabulary that relates to plant species that are in decline or faced with the prospect of extinction usually includes such terms as "threatened," "vulnerable," and "endangered." These categories and others relating to imperiled species have been used in different contexts by various governmental agencies, conservation organizations, and nature writers. The official International Union for Conservation of Nature and Natural Resources (IUCN) Red Data Categories (G.Ll. Lucas and H.Synge 1978; S.D. Davis et al. 1986) are the most widely used terms worldwide. In this classification, "endangered" taxa are those in danger of extinction and whose survival is unlikely if the causal factors continue operating, and "vulnerable" taxa are those believed likely to move into the "endangered" category in the near future if the causal factors continue operating. Taxa at risk and that have small world populations, but which are not yet sufficiently imperiled to be classified as "endangered" or "vulnerable," are placed into the category of "rare." Other categories accommodate taxa that are extinct, that were formerly imperiled but are now out of danger, or that are insufficiently known but suspected of being at risk.

In the United States, a somewhat different system is used to provide legal designations for officially listed taxa under the Federal Endangered Species Act (J.A. Bartel 1987). In this classification, an "endangered" taxon is in danger of extinction throughout all or a significant portion of its distributional range. Taxa are considered "threatened" if they are considered likely to become "endangered" within the foreseeable future. According to Bartel, because these terms denote a legal status for plants that have completed the listing process, they cannot be applied in the same sense to candidates for listing, or to those candidates for which a proposed regulation has been published.

Apart from these two widespread and official systems of rare plant classification, descriptive terms such as "endangered" and "threatened" have been used qualitatively and relatively interchangeably in various contexts (J.L. Reveal 1981; J.A. Bartel 1987; H.Koopowitz and H.Kaye 1990), so that their meanings have converged on a common definition in the minds of many members of the public. In addition, definitions have occasionally been modified for specific reasons, such as by administrative agencies concerned with the protection of species that barely enter the geographic areas under their jurisdiction. Classifications of conservation status may or may not imply legal status, depending on the situation at hand. In addition, classification as "endangered" for any one species may change in a few decades if recovery efforts are effective.

Other terms, such as "critically imperiled," "imperiled because of rarity," "rare," and "uncommon," are also used. The Nature Conservancy has established a numerical system of global and state-level element rankings with category definitions that are based on taxon range, populational numbers and sizes, and vulnerability, and that include these terms (G.W. Argus and K.M. Pryer 1990). "Sensitive" is commonly used by land managers in the western United States for plants that are being monitored but that may or may not be protected by state or federal law. "Rare" and "uncommon," used in a number of situations, are also variably defined. All of these terms have many different meanings and are not consistently applied in North America with regard to legal status or conservation needs. Therefore, the authors of taxonomic treatments in the Flora of North America have described individual situations for taxa that are of concern to conservationists, rather than attempting to use any "standard" terms without explanation.

Contributions to Plant Conservation Efforts

An analysis of the full spectrum of efforts to preserve North American flora at local, state/provincial, national, and continental levels is beyond the scope of the present chapter. Some aspects of this broad and complex topic were reviewed by various contributors in H.Synge (1981) and were summarized briefly by S.D. Davis et al. (1986). As noted above, the efforts of some private and governmental groups are actually aimed at preservation of habitats, rather than individual species, but the boundary between the two approaches is often indistinct.

International Contributions

As developed nations with well-established, diverse conservation programs, the North American countries are in a better position to assist the activities of international organizations in other less-developed countries than to require such assistance themselves. Nevertheless, several organizations with an international focus are engaged in plant conservation projects dealing with North American plants.

The activities of the Nature Conservancy and of the United Nations Man and the Biosphere Program are described below. The International Union for the Conservation of Nature and Natural Resources (IUCN), a private international group, has published several summaries on various aspects of world conservation that have included data on North America, such as its "red data" book on selected plant species (G.Ll. Lucas and H.Synge 1978) and its summary of national parks and protected areas (I.U.C.N. 1985). This organization, together with the World Wildlife Fund and several other organizations, has also formalized a strategy for plant conservation at botanical gardens (V.H. Heywood 1989). The Species Survival Commission of IUCN maintains a North American Plant Specialist Group to address regional issues involving plant conservation. The World Wildlife Fund, which originated as an offshoot of the IUCN, has become increasingly active in plant-related conservation efforts, including the publication of a summary of available information on all federally listed taxa of the United States (D.W. Lowe et al. 1990).

The countries of the Flora of North America region are all party to CITES. This trade agreement, which controls the international trade of rare plants and animals, was originally enforced in 1975 by 10 countries and now has nearly 100 signatory nations. Three appendices to CITES separate taxa into groups (categories I, II, and III), based on degree of rarity and threat from international trade. Often whole genera or families are listed, rather than individual species. Plants native to North America that are listed by CITES include some or all members of the Agavaceae, Araliaceae, Cactaceae, Crassulaceae, Ericaceae, Orchidaceae, Portulaceae, Sarraceniaceae, and Zamiaceae, which are among those families in the region most prone to overcollection for horticultural or medicinal purposes and for international trade (D.S. Favre 1989).

Efforts in Greenland

Within the Flora of North America region, the protection provided to plants and habitats varies. Greenland, officially Kalâtdlit-Nunât, has an arctic flora of about 500 species, of which 15 are endemic. It has no national legislation specifically designed to protect plants (S.D. Davis et al. 1986). The country, however, contains the largest national park in the world (S.D. Davis et al. 1986; fig. 10.1), the North East Greenland National Park, which covers more than 700,000 km², and by its size alone protects significant portions of the botanical diversity of the country. The Melville Bay Nature Reserve (10,500 km²) also preserves a large area of native landscape. The distribution and ecology of the relatively few endemic taxa have been well studied, but further research is necessary to assess the conservation status of most of these species.

Efforts in Canada

In Canada, with approximately 3500 native species of vascular plants, the situation is more complex. Lists of rare and endangered plants are available for all the territories and provinces through the Rare and Endangered Plants Project at the Canadian Museum of Nature, in Ottawa (G.W. Argus 1977). A recent, more comprehensive volume (G.W. Argus and K.M. Pryer 1990) summarizes the status of 1010 rare species on a countrywide basis. The assessment of the "endangered" or "threatened" status and the compilation of detailed status reports on approximately 440 high-priority taxa in the Canadian flora is also underway (for an example, see D.J. White 1987). These reports are being prepared under the auspices of the Subcommittee on Plants of COSEWIC, a consortium of provincial and territorial governmental agencies, the National Museum of Natural Sciences, the Fisheries and Oceans Department, the World Wildlife Fund Canada, the Canadian Nature Federation, and the Canadian Wildlife Federation that was formed in 1977 (F.R. Cook and D.Muir 1984).

No national legislation has been enacted to protect endangered plant species, for such protection is the jurisdiction of the provinces (A.L. Maurer 1985). All provinces have ecological reserve acts, and four have endangered species acts. Some sentiment exists, however, that the numerous regional laws and levels of administration are insufficient to preserve the nation's imperiled flora (G.W. Argus 1977). As explained by G.W. Argus and K.M. Pryer (1990), the greatest concentrations of rare plants in Canada occur in the topographically diverse mountain provinces of the west, and in the Great Lakes region of Ontario. Many of the plants of conservation concern to the country are confined to floristic provinces whose northern extremes barely enter Canada, and the main geographic distributions of such species are further south, in the United States. In Canada, the distribution of rare endemic plant species is shown on a province by province basis in figure 10.3, which implies the importance of the western provinces with regard to plant diversity.

In addition to a large number of local, provincial, and territorial reserves and parks, Canada contains large areas of federal reserves. Thirty-four national parks and national park reserves (fig. 10.1), some of them adjoining similar parks in the United States, protect nearly 2% of the 10 million km² total area of Canada (M.Finkelstein 1990). A comprehensive development plan for national parks in each of the 39 Canadian National Park Natural Regions has been completed (M.Finkelstein 1990) and projects an expansion of the national park system to protect the diversity of environments found in the country. Potentially, about 2.8% of Canadian lands will be protected in the national park system, if the plan is completed.

Efforts in the United States

Of the countries in the Flora of North America area, the United States has the best developed national legislation for plant protection. The federal Endangered Species Act was passed in 1973, and it has since been renewed and amended regularly. It is administered by the United States Fish and Wildlife Service. The Smithsonian Institution (1975) was charged with preparing an initial list of sensitive species, which was revised and made available to a broader audience (E.S. Ayensu and R.A. DeFilipps 1978). These initial lists contained 2099 and 2140 imperiled taxa, respectively, from the continental United States (3200 total taxa listed when Hawaii and Puerto Rico are included). These plants subsequently became candidates for potential listing as endangered or threatened under the Endangered Species Act (fig. 10.3). The list of federally protected and candidate species is periodically reviewed and published in the Federal Register (Fish and Wildlife Service 1990, 1992).

The federal Endangered Species Act is a powerful law in the sense that species in critical endangerment of extinction are evaluated for inclusion on a scientific basis, without regard for extrinsic factors. The act provides legal protection for listed taxa on federal lands, in cases of other land use involving federal funding, and particularly for horticulturally desirable taxa in interstate commerce. Other provisions of the act include the definition of "critical habitat" for taxa during the listing process, thereby guiding agencies in the selection of sites needed to protect each species, and also a mandate for formulation of a "recovery plan" for endangered and threatened taxa, aiming to restore eventually the numbers of individuals and populations of each listed plant so they are no longer in danger of extinction.

A well-known example of the power of the Endangered Species Act involves Pedicularis furbishiae (Furbish's lousewort, Scrophulariaceae), which was initially thought to be extinct but was rediscovered in 1976 growing near the type locality in Maine. (The plant is also known to grow in adjacent New Brunswick, Canada). It was listed as federally endangered in 1978. The discovery of several populations of this species along the St. John River in an area that was to be flooded as part of a federally funded dam project was instrumental in the denial of a federal permit for that project (D.W. Lowe et al. 1990).

The evaluation and listing process for individual species is lengthy and complicated, requiring extensive consideration and documentation before a species becomes officially protected. Where the need arises, a means exists to provide "emergency listing" for plants in danger of immediate extinction. Most often, however, the protection process moves slowly. Of the more than 2000 taxa initially accepted as candidates in 1975, only 58 had actually been listed as endangered or threatened by 1981 (J.F. Fay 1981); the most recent summary of officially listed taxa (Fish and Wildlife Service 1989) has only 169 taxa from the continental United States. Additional species have also been nominated and added to the original list of candidates (Fish and Wildlife Service 1990), and some of the original candidates have been deemed unworthy of listing after careful study.

Presently, after consideration at the regional level (fig. 10.2), a species may be entered onto the list of candidate plants for federal protection as "category 2." Here taxa may remain for variable periods of time as more information is gathered. If found not to be in need of listing because of persuasive evidence of extinction, taxonomic reevaluation, or reassessment of abundance, a taxon is moved to category 3 and is dropped from active consideration. If evidence accumulates for potential imminent extinction of the taxon, it is moved to category 1, preparatory to final listing as "threatened" or "endangered."

Prior to final listing, a proposal for each taxon must be published in the Federal Register, and governmental agencies, scientists, and the public are given a period of time for comments prior to a final ruling. Taxa for which a proposal package has been published receive a limited form of protection, which is focused on notification of potential threats on federal lands or federally funded projects and nonmandatory recommendations concerning protection (J.A. Bartel 1987). Proposed taxa and those in categories 1 and 2, however, often receive considerable protection, for state and federal land managers often incorporate consideration of these plants into local management programs.

Not all states in the United States have laws protecting sensitive plant species. Those that do, however, contribute to a bewildering variety of laws, ranging from legislation designed to protect particular species or families to more general laws against picking or injuring native plants on public property (P. Olwell et al. 1992). In some states, federally listed species are also given protection on state lands. Although written with good intention, many state plant protection laws in effect are generally considered inadequate or unenforceable (W.D. Countryman 1977; J.W. Hardin 1977) and are undergoing revision.

The United States has large areas of public lands, on which natural plant communities receive varying levels of protection. Each state has many state and local parks and preserves, the latter often coordinated through some form of natural areas system. About one-third of the country's 9,363,000 km² is owned by the federal government (S.D. Davis et al. 1986). R.E. Jenkins (1975) estimated that approximately two-thirds of the federally endangered plants occur on federal lands. Areas receiving the greatest degree of protection include the national parks (fig. 10.1), monuments, lakeshores, seashores, scenic rivers, and wildlife refuges, which total nearly 650,000 km² (I.U.C.N. 1985).

Most other federal lands, such as those in national forests or those controlled by the Bureau of Land Management, are managed under a policy of "multiple use management." Permission for grazing, lumbering, mining, and other practices that by their nature result in environmental modification are evaluated on a per parcel basis. It is on these lands that many plant species gain protection. An increasing number of "research natural areas" and "wilderness areas" are being designated on these and other federal lands, to set aside the least disturbed parcels for stricter preservation of their natural landscapes (E.S. Ayensu 1981). With regard to plants, most administrative units of land-managing federal agencies now also have staff botanists whose responsibility is monitoring sensitive species and preparing management plants for their conservation.

Natural Heritage Programs

In the United States and Canada, all states and provinces have agencies designed to deal with management of natural resources. Conservation programs for nongame species or species of little commercial importance often comprise minor elements in agencies whose principal missions concern management of timber resources or fish and game animals. An increasingly important contribution of these state agencies to plant conservation is the assessment and monitoring of regionally and globally imperiled taxa through the efforts of a network of Natural Heritage Programs (L.E. Morse 1981; P. Olwell et al. 1992).

These programs were first developed in 1974 in the United States, in 23 states, by the Nature Conservancy (see below), and now exist in every state. They are also being implemented in Canada, where they are called Conservation Data Centres. The first such centre was established in Quebec, in 1988, and two others, in British Columbia and Ontario, followed in 1990 (P.Hoose and S.Crispin 1990). Saskatchewan added a centre in 1992. We hope similar programs will be implemented in the remaining provinces and territories in the near future.

Most of the Natural Heritage Programs and Conservation Data Centres were initiated in cooperation with the relevant state or provincial department in charge of fish and game, conservation, or natural resources, and then turned over to these governmental agencies for administration after about two years of operation. Their mission involves completion of relatively detailed inventories of various natural features, including rare plants, with specific site information on each element stored in a database and on topographic maps.

This information is then made available to land managers, scientists, and project planners, for use in environmental impact assessments and other conservation-related activities. The data thus generated have facilitated compilation of more accurate lists of regionally and globally endangered species occurring in each state. Many of these lists have been published (E.S. Ayensu 1981). They have also helped to identify the regions most critically in need of further exploration. Even in well-developed countries such as Canada and the United States, knowledge of the biota is very uneven, for there are areas that are relatively inaccessible and biologically poorly known. Considerable botanical survey work remains to be completed in such areas as northern British Columbia, much of the eastern portion of the Northwest Territories, parts of Labrador and Newfoundland, and remote areas of the southwestern United States.

Contributions by Private Organizations

In addition to local, state, and national governmental efforts for plant conservation, numerous private organizations with similar goals are active in each country. The activities of such organizations range from stimulating public awareness and education to legislative lobbying and even the preparation and filing of lawsuits. Some also purchase properties for preservation or collect germplasm of imperiled species for storage or cultivation.

The largest and best known of such organizations is the Nature Conservancy, which was started in 1950 by a group of concerned scientists and environmentalists (L.E. Morse 1981). The group began in the United States, where there are now state chapters throughout the country. It is increasingly active internationally, particularly in Canada, Central America, and South America. The Nature Conservancy practices habitat and endangered species conservation primarily through the purchase of outstanding parcels of land, which are then either retained or sold or donated to various public agencies charged with environmental protection. Unfettered by extensive governmental procedures and conflicting public pressures, the Conservancy's ability to respond quickly to opportunities has resulted in the preservation of many parcels of land that might otherwise have been altered permanently by human activity.

The Nature Conservancy has also been active in several other ways. The organization has been a leading force in research on various types of active versus passive management for preservation of natural landscapes and endangered elements on its lands (L.E. Morse 1981). It has established land registry programs in most states, in which private landowners receive assistance and recognition for important habitats on lands that they own and agree to manage for preservation of natural features. The state Natural Heritage Programs initiated by the Conservancy have been instrumental in the accumulation of detailed site information on special elements occurring in each state. Because each state program uses consistent nomenclature, identical databases, and the same definitions for ranking global and regional endangerment (as reviewed in G.W. Argus and K.M. Pryer 1990), the Conservancy has been able to pool regional data into a national database, the most complete and informative of its kind. This national information system, known as the Heritage Data Center Network, has become an extremely important tool for summarizing needs and priorities in both species and habitat conservation.

Several groups have focused on the study of endangered species through the preservation of germplasm in storage and cultivation, including the Center for Plant Conservation, the Canadian Plant Conservation Programme, the National Wildflower Research Center, and various individual botanical gardens and arboreta. The best known of these is the Center for Plant Conservation (CPC), which was organized in 1985, and coordinates the efforts of more than 25 regional member institutions to maintain in cultivation critically imperiled taxa for conservation purposes (L.R. McMahan 1991).

Germplasm from more than 300 taxa is stored in a seed bank (in coordination with the United States Department of Agriculture's National Seed Storage Laboratory), and cultivated samples at each botanical garden and arboretum are grown for research and educational purposes. One objective of the CPC's program is the reintroduction of subject taxa into the wild, and several such projects are already underway (L.R. McMahan 1991). The group has promoted research on various sensitive taxa as well. The CPC also has developed a comprehensive database on rare plants to complement its other work.

Present and Future Challenges

Certainly North America is not unique in regard to the degradation of the natural environment and the loss of biological diversity. Human impact on the environment is relentless throughout the world, and loss of natural habitat in the tropics may ultimately have a greater effect on stability of global ecosystems than will modifications of the environment in the temperate regions. The developed nations of North America, however, bear a responsibility to take lead positions in responsible conservation within their countries and worldwide.

In spite of the programs outlined above, much remains to be done on the short term to preserve biotic diversity in North America's shrinking natural landscape. Many of the approaches that have been identified as priorities have already been given some attention, but they require further expansion and completion. One extremely important project that has long been cited as necessary to plant conservation efforts is the completion of a single floristic treatment that summarizes and correlates baseline data on taxonomy, biogeography, and ecology of plants for a major portion of the continent in a way that no regional account can. The completion of a flora of North America will result in a comprehensive account of the plants of the region that will help public land managers, private citizens, biologists in academic and research institutions, and legislators to arrive at sound decisions regarding matters of important environmental concern (N.R. Morin et al. 1989).

In addition to this great synthesis, considerable primary research is still necessary on individual plant species of concern. For many endangered taxa, detailed studies of population genetics, taxonomy, ecology, biogeography, and life history factors are still necessary to supplement existing observations that these taxa are uncommon in nature (E.S. Ayensu 1981). Such information is necessary to assess why a species is restricted in range, what the causes of endangerment are, how much genetic variation is left in the remaining populations, and what the success of certain recovery efforts might be. Research programs at various universities and colleges in North America, as well as the efforts of botanical gardens and arboreta, already are making important contributions to our knowledge of some critical species, often in coordination with governmental agencies (L.R. McMahan 1991).

In Canada, the World Wildlife Fund Canada, and the Canadian Fish and Wildlife Service have supported the development of the COSEWIC status reports, which were initiated in 1977. Some of these funds have supported needed basic research. In the United States several federal agencies, among them the United States Forest Service, the Bureau of Land Management, and particularly the United States Fish and Wildlife Service, have allotted public funds for status reports and the development of information regarding plant species on the federal candidate list. The Endangered Species Act also mandates research on various means to effect recovery of federally endangered and threatened taxa to the point where they are no longer at risk. The Center for Plant Conservation has been instrumental in the promotion of research on various critically endangered species under cultivation at botanical gardens and arboreta.

The question of species recovery also requires much further research. The assessment and monitoring of endangered species in nature does not ensure the perpetuation of these taxa. In many cases, cessation of habitat degradation may be sufficient to ensure continued existence of a declining species. In other situations, active management of a habitat, such as controlled burning, may be necessary to effect increases in population size or to alter existing habitats to render them more favorable to colonization by a particular species. For some species, measures to reintroduce populations into nature from cultivated sources may be necessary to ensure that adequate numbers of individuals are present for successful reproduction or simply to prevent extinction in the wild.

The process of plant reintroduction first requires collection and maintenance of samples from existing populations, for which botanical gardens and arboreta are best suited. The concept of plant reintroductions is not without controversy. Questions arise about the effectiveness of introducing germplasm from one portion of the range of a species, where genetic differentiation in response to ecological factors may have occurred, into a geographically distant area, where selection factors may differ sufficiently to thwart long-term success. The potential effects of such foreign germplasm on the fitness of remaining, nearby, natural populations of the same taxon also remain controversial.

No matter how much information about endangered species is generated by scientists, the fate of preservation efforts ultimately depends on the ability of conservation organizations and agencies to convince private industry, governments, and the general public of the critical need to set aside sufficiently large and numerous areas of suitable habitat and to support philosophically and financially the work required to achieve conservation goals. Although initially costly, in the long run humanity will benefit. Education programs designed to inform the public and sensitize people to critical problems in the environment on which they depend require continual expansion and innovative revision to remain effective. Botanical gardens and arboreta have unique opportunities to focus public attention on plant conservation by bringing visitors and members into personal contact with the individual species, in helping them to understand the problems through the use of interpretive and educational materials, and even by getting the public involved in volunteer programs aimed at plant and habitat conservation.

An informed public has political power. Through the democratic process, voters are now beginning to insist that land owners and managers alter land-use practices toward more environmentally sustainable harvests of natural resources, toward minimization of impacts of erosion and nutrient loss in soils, and toward reductions in other destabilizing forces that accompany extensive development without ecological consideration.

The role of biosphere reserves is especially worthy of note in this regard. These reserves are part of the Man and the Biosphere Program, begun in 1971 by the United Nations Educational, Scientific, and Cultural Organization (UNESCO). Unlike other nature preserves, the biosphere reserves are generally under multiple ownership. They have core areas (usually portions of some existing national park or wilderness lands) managed strictly for preservation of natural ecosystems, a surrounding buffer zone whose management objectives may include research, recreation, tourism, etc., and a transition zone in which the land management is intended to facilitate harmonious integration of the reserve into the existing land-use practices of the surrounding region (J.R. Vernhes 1989).

The often complex tapestry of adjacent areas ascribed to different zones theoretically should make biosphere reserves useful for research on both pristine and disturbed ecosystems, as well as for public education on land management. Obviously, the selection of areas whose natural landscapes and land-use histories are adequate for this sort of program is a key factor. At present, in the Flora of North America region, four Canadian areas and about 40 areas in the continental United States, mostly in conjunction with existing national parks, have been designated as biosphere reserves. Several potential reserves are presently under evaluation.

Public perceptions also need to be balanced between short-term goals for preservation of presently endangered species and the need for a long-term perspective, to allow treatment of both the individual symptoms of each species and the more devastating general loss of natural habitats and biodiversity. Although the various programs outlined above present evidence of widespread interest and actions for plant conservation in North America, a feeling among many conservationists suggests that much more needs to be done, quickly, to address biodiversity issues in the region properly.

Often, the sense of impending doom expressed by some environmentalists stems from dissatisfaction with seeming priorities of society, particularly the continuous destruction of natural resources through exploitation for commercial purposes. For industrially developed countries, the demands on big business to remain competitive in national and international markets often result in the elevation of economic priorities in direct conflict with needs required to maintain environmental health. In underdeveloped countries the situation is often much worse, for the survival of a large percentage of the inhabitants often depends on the progressive destruction of pristine and complex ecosystems. Ultimately, North American countries and those elsewhere in the world are shackled by a series of constraints involving growing populations, fluctuating economies, and the complexities of politics. Sometimes, short-term goals for various kinds of environmental conservation are deemphasized in the fight for economic and personal survival. This short-sighted approach to problem solving cannot, however, continue indefinitely without virtually the complete loss of biological diversity.