Ex Situ Plant Conservation: Supporting Species Survival In The Wild

By Kayri Havens-Young, Michael Maunder, Peter H. Raven and Center for Plant Conservation

Faced with widespread and devastating loss of biodiversity in wild habitats, scientists have developed innovative strategies for studying and protecting
targeted plant and animal species in "off-site" facilities such as botanic gardens and zoos. Such ex situ work is an increasingly important component of conservation and restoration efforts.

Ex Situ Plant Conservation, edited by Edward O. Guerrant Jr., Kayri Havens, and Mike Maunder, is the first book to address integrated plant conservation strategies and to examine the scientific, technical, and strategic bases of the ex situ approach. The book examines where and how ex situ investment can best support in situ conservation. Ex Situ Plant Conservation outlines the role, value, and limits of ex situ conservation as well as updating best management practices for the field, and is an invaluable resource for plant conservation practitioners at botanic gardens, zoos, and other conservation organizations; students and faculty in conservation biology and related fields; managers of protected areas and other public and private lands; and policymakers and members of the international community concerned with species conservation.

• Language: English
• Publisher: Island Press
• Release date: Feb 22, 2013
• ISBN: 9781597267564

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together.

INTRODUCTION

Ghillean T. Prance

The late Stephen J. Gould had agreed to write this essay, but unfortunately this great zoologist, evolutionary biologist, and interpreter of science died before he had time to complete it. I am sorry not to have had the opportunity to read another essay by him. Although I cannot possibly emulate Gould’s wonderful style of writing, I find myself wondering what an evolutionary biologist and zoologist would have written about ex situ plant conservation. The greatest drawback to ex situ conservation is that in most cases it halts or distorts the natural process of evolution. Evolution was Stephen Gould’s particular specialty, and he wrote many articles about the detailed interactions between organisms to illustrate this process. The process of evolution is modified when we are forced to store plant species in seed banks or even grow them in botanic gardens away from their natural range and specific ecosystem. Perhaps we are causing a gap in the evolutionary process that will eventually be regarded as another period of dormancy to support the theory of punctuated equilibrium that Gould (2002) was so instrumental in developing. In any case, it is an honor to have the opportunity to remember here this great theoretical biologist and defender and interpreter of the natural world.

Most conservationists readily admit that in situ conservation, the conservation of habitats and ecosystems with their constituent populations of species, is the highest priority. This approach is certainly supported by the Convention on Biological Diversity (CBD), of which Article IX states that parties shall use ex situ techniques "as far as possible and as appropriate, and predominantly for the purpose of complementing in situ methods" (Glowka et al. 1994, p. 52). The emphasis of the convention is definitely to recommend in situ rather than ex situ conservation wherever possible. If this is the case, why do we need a book about the science of ex situ conservation? The sad truth is that ex situ conservation is becoming ever more important as a tool to help maintain biodiversity.

Human-caused habitat loss and degradation and invasive species are accelerating the loss of species (Tilman and Lehman 2001). In addition, many habitats are vulnerable to alteration through human-caused climate change, and these changes are occurring at a pace that is beyond the dispersal ability of many plant species (Crumpacker et al. 2001). Therefore, a book that helps to develop ex situ conservation as a practical science is of vital importance to conservation.

As I write this on the beautiful island of Kauai in Hawaii, sitting in the National Tropical Botanical Garden, I am surrounded by examples of the practical challenges of ex situ conservation. The majority of the threatened rare species in Hawaii exist only as a very small population of questionable viability. It is to be hoped that some of these, such as Cyanea pinnatifida (Cham.) F. Wimmer (Campanulaceae), which was reduced to a single individual, can be rescued. The success of ex situ conservation has already been demonstrated with the nene, or Hawaiian goose (Branta sandivicen-sis ). After captive management and reintroduction this bird has made a remarkable recovery from what many skeptics thought was an impossibly small population. Today I do not have to visit the Wildfowl and Wetlands Trust in England to see nene, but each time I visit Koke’e or Kilauea on Kauai I see these beautiful birds that have been rescued from the path of extinction. In the case of Cyanea pinnatifida (Campanulaceae) there is some hope because hundreds of individuals have been propagated from the single founder by the Lyon Arboretum in Honolulu. The case of Hibiscadelphus woodii (Malvaceae) Lorence & W. L. Wagner is less hopeful. Of the four wild individuals discovered, which were accessible only through the use of climbing ropes, only one remains alive, and no one has been able to propagate it. Similarly, Kanaloa kahoolawensis (Fabaceae) Lorence & K. R. Wood had a wild population of only two individuals when it was discovered in 1992, only one of which survives, but there are now two individuals in cultivation. Hawaii, like so many devastated oceanic islands, is the ultimate challenge to species conservationists, whether proponents of in situ or ex situ methods.

Growing near to me are some pots full of the attractive pachycaul member of the Campanulaceae, Brighamia insignis (Campanulaceae) A. Gray. The creamy yellow flowers have a long, narrow corolla tube typical of hawkmoth-pollinated flowers. Unfortunately, it is thought that the sphingid moth that pollinates this plant is extinct or near extinction. No other moth is able to pollinate this species. Artificial pollination can be done easily here in the botanic garden, but in the wild it often entails rappelling down cliff faces. Many of the threatened rare plants that we are trying to save have specialized pollination mechanisms that cannot work with generalist pollinators. Even if these pollinators are still extant, one cannot preserve insects or hummingbirds in cold storage, as one can with seeds. It is often easy enough to keep a plant species alive but much harder to maintain the interactions it needs for pollination, seed dispersal, and, indeed, other mutualistic relationships with animals. Without these processes, evolution is halted. Perhaps a much closer collaboration is needed between workers in ex situ conservation of animals and of plants.

All these examples from Hawaii emphasize the important role of botanic gardens in conservation. I have been on the staff of various botanic gardens for almost 40 years. During that time the environmental and political conditions for in situ conservation have deteriorated rapidly, and the number of species threatened with extinction has increased dramatically. Many botanic gardens have responded to this challenge and have established added conservation programs. We also have support from organizations such as the Center for Plant Conservation (CPC), the International Union for the Conservation of Nature (IUCN) Species Survival Commission (SSC), the International Plant Genetic Resources Institute (IPGRI), and Botanic Gardens Conservation International (BGCI). These entities are helping many botanic gardens and other ex situ practitioners improve their conservation programs, such as BGCI’s global agenda for botanic gardens (BGCI 2001). A botanic garden that does not emphasize plant conservation in its mission program, whether in education or in the ex situ conservation of species or habitats, is not adequately responding to the challenges of today’s world.

As components of both agricultural and wild landscapes, plants are fundamental to human well-being. Ex situ conservation cannot afford to be only a process of collection and storage; the release of material for repatriation and reintroduction provides the ultimate service to the clients of ex situ conservation, be they protected area managers, private landowners, or rural communities (Maunder 1992; Sperling 2001). The science of ex situ conservation preserves not only wild species but also the huge number of varieties of domesticated species that humans have developed over the past 10,000 years, since the beginnings of agriculture. The importance of conserving landraces of crop species has been demonstrated recently in Afghanistan, where many of the locally adapted cereal varieties have been destroyed by drought and warfare. On top of the recent conflict, 2001 was the third year in a row in which the rains failed. This caused the loss of the majority of the seeds on which the farmers depended. Although the weather improved, the farmers still lacked a basic agricultural need: seeds of their traditional crops. Worse still, the National Gene Bank of Afghanistan was destroyed in 1992. Over many years Afghani farmers had selected varieties of their crops of wheat, chickpeas, barley, lentils, and fava beans that were appropriate to local conditions and taste; these included strains of crops that would grow in some of the most unfavorable places for agriculture. Fortunately, in the 1970s Geoffrey Hawtin, who is now director-general of the IPGRI in Rome, traveled throughout Afghanistan to collect seed for use by crop breeders around the world. Hawtin’s visit was just before the Soviet occupation that would have stopped such a venture. Some of Hawtin’s seeds were deposited at freezing temperatures in the seed bank of the International Center for Agricultural Research in the Dry Areas (ICARDA). Many of these seeds are being returned to their country of origin to help rebuild agriculture there. Although some of ICARDA’s improved varieties of wheat are also helping Afghanistan, there are many places where specially selected local landraces and varieties will do better. The small quantities of seeds of these varieties will be crucial to restoring agriculture in Afghanistan.

Many of the most useful plants to humanity are the ones that are most threatened with extinction because of overuse. This is particularly true of medicinal plants. More than 80 percent of the developing world still relies on traditional medicines, mainly from plants, for their primary healthcare (Farnsworth and Soejarto 1991). Even in the developed world, the use of plant-based medicinal systems such as Chinese and Ayurvedic medicine is increasing. As a result, some of these important healing plant species are overcollected. The Royal Botanic Gardens, Kew, and Guy’s Hospital in London have set up an authentication center for Chinese medicines to combat the increasing trend of substitution of fake compounds because where the true medicinal plants are becoming scarce, other plants are often used. The ex situ cultivation of some of these plants can reduce the pressure on wild populations and improve the quality of life for many communities.

A program that does this is Living Pharmacies (Farmácia Viva) of Brazil. It began in the city of Fortaleza, in northeastern Brazil, where a chemist, Professor J. Mattos, and a medical doctor, Dr. Adalberto, began growing plants and preparing medicines from them to treat people in one of the large slums of the city. They employ formerly abandoned street children to cultivate the plants in return for an education and food. The medicinal plant gardens that have been set up in several places in Brazil are reducing pressure on the species in the wild and performing a major social function by providing affordable medicines to local people. I have also seen medicinal plant gardens in India that are producing the ingredients of Ayurvedic medicines while reducing the need to collect wild-sourced material. We need to have a broad concept of ex situ conservation and to include projects such as these in our thinking about how to protect threatened species and resources, especially when we are dealing with species of economic use in poor areas.

In recent years ex situ conservation has become a much more precise science with a wonderful array of tools. Foremost among these are molecular techniques that enable us to assess and monitor the genetic variation within populations. This is absolutely critical when we are dealing with small populations, whether in situ or ex situ. When only a few individuals exist, it is vital to make genetically appropriate crossings to obtain healthy progeny and to capture what little genetic diversity is left. Molecular methods are also useful in monitoring the purity of a species and ensuring that hybridization has not taken place. Hybridization is a risk when plants are grown in botanic gardens, and often not enough care is taken to avoid it. Tissue culture, which we have used for some years, is an invaluable tool for propagating rare species and obtaining disease-free lines. Seed storage methods have greatly improved in the last few decades, and there has been much research on dormancy breaking and recalcitrance.

Wherever possible, ex situ conservation should be regarded as a temporary method, and practitioners should always be looking for ways to restore species to their natural habitats. In order for this to happen it is essential that the science of ex situ conservation not be isolated from that of in situ conservation and that an integrated approach be adopted (sensu Falk 1987). Many botanic gardens today have areas of natural vegetation within their boundaries or in adjunct campuses. This is ideal because it involves them in the practice of in situ conservation, and as a result their ex situ work usually benefits as well. The prime example of this is seen in the South African network of botanic gardens, which has a garden with large natural areas situated in each major ecosystem.

I am pleased to be working with the Eden Project in Cornwall, England, because it is performing an important function for ex situ conservation: transmitting information to the public. Eden exists to promote the importance of plants to people and the sustainable use of all plants. This successful project, which received more than 2 million visitors in its first year of operation, is bringing a strong message of conservation to its visitors. To promote such a message, it is also necessary to practice conservation and sustainable management techniques. In the 5-acre rainforest biome you will find such threatened plants as Trochetiopsis ebenus (R. Brown ex Aiton f.) W. Marais (Sterculiaceae), the Saint Helena ebony, which was reduced to only two individuals in the wild, and Impatiens gordonii Horne (Balsaminaceae) from the Seychelles, of which only a few individuals remained. The Eden Project has developed partnership agreements with institutions in those island territories and in various other places from which it is exhibiting plants. In addition to multiplying material for reintroduction to the wild, we hope to bring the Impatiens species to the horticultural market to benefit conservation in the Seychelles. Visitors to Eden learn about the threats to these and other threatened rare plants and about what is being done to rescue them from extinction. Eden is both practicing and exhibiting ex situ conservation. There is still not enough of the latter in botanic gardens and reserves, and conservation would benefit greatly if more understanding could be instilled into the general public through the display and interpretation of the rare plants they grow.

This book recognizes the limitations of ex situ conservation while urging us not to undervalue it. That ex situ conservation is vitally important and has prevented the extinction of many species of plants and animals is undeniable. Starting with Franklinia altamata Marshall, last seen in the wild in 1803, gardens have enabled the survival of many species that have become extinct in the wild. A recent example is the beautiful crocus-like Tecophilaea cyanocrocus Leyb. from Chile, a species that is quite common in horticulture but extinct in the wild (Maunder et al. 2001). There is an important niche for ex situ conservation, and I hope that this volume, the third CPC book on plant conservation, will promote it as a tool to support both species and habitat conservation.

REFERENCES

BGCI (Botanic Gardens Conservation International). 2001. International Agenda for Botanic Gardens in Conservation. Kew, UK: Botanic Gardens Conservation International.

Crumpacker, D. W., E. O. Box, and E. D. Hardin. 2001. Implications of climatic warming for conservation of native trees and shrubs in Florida. Conservation Biology 15(4):1008–1020.

Falk, D. A. 1987. Integrated conservation strategies for endangered plants. Natural Areas Journal 7:118–123.

Farnsworth, N. T., and D. D. Soejarto. 1991. Global importance of medicinal plants. Pages 25–51 in O. Akerele, V. H. Heywood, and H. Synge (eds.), The Conservation of Medicinal Plants. Cambridge, UK: Cambridge University Press.

Glowka L., F. Burhenne-Guilman, H. Synge, J. A. McNeely, and L. Gündling. 1994. A Guide to the Convention on Biological Diversity. Environment Policy and Law Paper no. 30. Gland, Switzerland: IUCN.

Gould, S. J. 2002. Punctuated equilibrium’s threefold history. Pages 1006–1021 in S. J. Gould, The Structure of Evolutionary Theory. Cambridge, MA: Harvard University Press.

Maunder, M. 1992. Plant reintroduction: an overview. Biodiversity and Conservation 1:21–62.

Maunder, M., R. S. Cowan, P. Stranc, and M. F. Fay. 2001. The genetic status and conservation management of two cultivated bulb species extinct in the wild: Tecophilaea cyanocrocus (Chile) and Tulipa sprengeri (Turkey). Conservation Genetics 2:193–201.

Sperling, L. 2001. The effect of the civil war on Rwanda’s bean seed systems and the unusual bean diversity. Biodiversity and Conservation 10:989–1009.

Tilman, D., and C. L. Lehman. 2001. Human caused environmental change: impacts on plant diversity and evolution. Proceedings of the National Academy of Sciences of the United States of America 98(10):5433–5440.

PART ONE

The Scope and Potential of Ex Situ Plant Conservation

Early perceptions of ex situ (off-site) plant conservation as a largely irrelevant novelty or possibly even a well-meaning but counterproductive distraction are giving way to a growing awareness that properly managed off-site collections can make the critical difference between extinction and survival. The diverse tools of ex situ plant conservation are a means to an end—survival in the wild—and a vital part of larger integrated conservation efforts.

Part I reflects the remarkable advances that ex situ plant conservation has made. Beginning with application to a small number of unusually threatened species and practiced as a standalone approach, and serving by default as a management cul-de-sac (see Chapter 1, this volume), ex situ plant conservation is increasingly being used to support the integrated conservation of regional plant diversity (Chapters 3 and 4, this volume). Over the almost 500-year history of the modern botanic garden, the classic venue for ex situ plant conservation, curatorial principles and professional codes evolved slowly until the last 40 years, when we have seen a dramatic revolution in both professional ethics and the application of conservation science (Chapter 1). As outlined in Chapters 1 and 3–5, this revolution has been driven in part by an internal recognition that ex situ conservation is a duty for botanic gardens and an external expectation by both the public and conservation agencies.

Set against the backdrop of an increasing appreciation of the sheer magnitude and increasing rate of species loss, the Endangered Species Act (ESA) in the United States and the ratification of the international Convention on Biological Diversity (CBD) can be viewed as two of the greatest external stimuli for ex situ plant conservation. The legal requirement of the ESA to recover threatened species in the United States provided impetus to try new approaches. More recently, and through the CBD’s national biodiversity strategies, has come explicit recognition that ex situ conservation is a legitimate and sometimes essential tool for species conservation and a valuable support to in situ conservation efforts. In turn, both of these extraordinary instruments are derived from decades of concern about the environment and from the intellectual and scientific frameworks developed by international agencies such as the World Conservation Union (IUCN), the International Plant Genetic Resources Institute (IPGRI), and Botanic Gardens Conservation International (BGCI). Whereas the international conferences of the 1970s by IUCN and others spurred the development of ex situ conservation in recent decades, the work of Vavilov and others in the early 1900s laid the strategic and scientific framework for ex situ plant conservation. It is on these foundations that national networks such as the Center for Plant Conservation (CPC; Chapter 4, this volume) and regional government agencies such as the State of Western Australia (Chapter 3, this volume) have advanced the field. The experience of both the CPC and Western Australia illustrates a growing mode of professional practice, an essentially collaborative ethic based on delivering services to conservation agencies with the objective of securing wild populations and holding viable insurance collections as a backup to wild stocks.

The ethical context of ex situ conservation, reviewed by Rolston in Chapter 2, is a dynamic and sometimes troubling view, but one that provides the intellectual and moral framework for much of plant conservation. Rolston explores the philosophical underpinnings of the commonsense recognition that biodiversity loss is to be avoided and that wild populations are inherently more valuable, and informative, than cultivated representations. Based on lessons learned in the zoo community, in Chapter 5 Stanley Price and colleagues advance the ethical debate beyond the immediate concerns about species conservation and show how ex situ efforts and institutions can be used to leverage support for habitat and ecosystem conservation, both locally and globally. These and other advances help to move us beyond the put a plant in a pot and the species is saved stereotype toward a realization that ex situ activities are critical to integrated plant conservation. Success ultimately will be measured not just by the number of taxa stored safely but, more importantly, by how well ex situ efforts contribute to the overall effort to maintain biodiversity in the wild.

Chapter 1

Ex Situ Methods: A Vital but Underused Set of Conservation Resources

MIKE MAUNDER, KAYRI HAVENS, EDWARD O. GUERRANT JR., AND DONALD A. FALK

Botanic gardens and other ex situ facilities such as seed banks are among the most extensive yet underused plant conservation resources in the world. For them to make a truly meaningful difference in how much plant diversity survives into the next century, ex situ plant conservation providers need to not only use the most effective and efficient means possible, but also increase their institutional capacity. In a sobering global review of the threats to biological diversity, Myers et al. (2000: 853) found that the number of species threatened with extinction far outstrips available conservation resources, and the situation looks set to become rapidly worse. This statement summarizes the challenge facing ex situ conservation at a time when the absolute need for in situ conservation has never been greater and the threats facing species diversity are increasing in type, severity, and scale.

The world’s botanic gardens and other ex situ facilities, such as seed banks, are among the most concentrated sites of species richness on the planet, in effect artificial centers of species diversity. The world’s 1,800 botanic gardens hold an estimated 2.5 million accessions of growing plants representing about 80,000 species (Wyse Jackson 2001). These vast collections have been accumulated over many decades and represent a huge investment in human resources and infrastructure. This book reviews the effective role of ex situ collections and assesses the values and limitations of ex situ plant conservation techniques.

The vast majority of ex situ samples, even those intended for conservation, have been collected on an ad hoc basis because they may be needed in the future for some unspecified purpose by an unspecified client. In addition, these collections are heavily skewed toward the cultivation of small and non–genetically representative samples of horticulturally amenable taxa and often suffer from poor documentation (Maunder et al. 2001b, 2001c). The majority of threatened species held in botanic garden collections are not specifically managed for conservation purposes and are characterized by a number of shared genetic and demographic characteristics (Box 1.1). However, the composition, status, and management of collections are rapidly improving as more facilities adopt conservation responsibilities. The recurring theme of this book is clearly outlined by Stanley Price et al. in Chapter 5: Where and how can ex situ investment make the most difference to in situ conservation?

Plant conservation facilities operate under the premise that they contribute conservation services to a variety of different clients. The primary role, retaining samples of wild plant diversity under artificial and accessible conditions, has been ratified in a number of professional guidelines (BGCI 2001) and international policy documents (IUCN/UNEP/WWF 1980, 1991; Glowka et al. 1994). However, these services are provided by a range of institutions and facilities of diverse historical heritage that share few common standards or protocols for the management, documentation, and display of threatened plant material. The majority of ex situ facilities were developed and still serve as facilities for growing and displaying token or at least genetically nonrepresentative samples of taxonomic diversity. The challenge is to use the most effective tools and processes and to serve these agreed roles of maintaining offsite collections and making them available for restoration and other conservation purposes.

The number of ex situ conservation facilities has increased dramatically in recent years (Wyse Jackson 2001), and they have become increasingly integrated under national and regional conservation initiatives. Nevertheless, many authorities hesitate to use them as a fundamental and effective component of plant conservation. This reluctance may originate from a number of perceptions. First, that ex situ conservation may undermine the integrity of, and need for, in situ conservation by devaluing wild populations and habitats. Second, it may reflect a lack of professional confidence in the technical ability of ex situ facilities to hold genetically diverse samples of threatened plant germplasm over extended periods of time. Much of the concern probably is based on a lack of understanding of what ex situ options exist and what their strengths and limitations are. For instance, storing seed is very different, in terms of both financial costs and biological risks, from maintaining a cultivated collection. Third, ex situ collections can be viewed as potential conservation liabilities, a source of new invasives and pathogens that can affect wild populations and habitats (Reichard and White 2001).

BOX 1.1

Characteristics of Threatened Plant Populations in Botanic Gardens

Populations are small and often derived from a small number of closely related founder individuals.

The cultivated stocks are subject to fluctuating population size as a result of changing horticultural fashions and episodic mortality events.

Often little or no associated ecological or biological information is available to guide ex situ managers in cultivating and managing the stocks.

There is little information on the history of the taxa in cultivation and often no satisfactory horticultural protocols.

Individuals are scattered through a number of collections with varying horticultural and curatorial capacity and hence differing patterns of regeneration and mortality.

Individuals are susceptible to artificial selection, genetic drift, inbreeding, and hybridization with congenerics.

Persistence in collections is highest for horticulturally amenable taxa and particularly for taxa with display or commercial value.

Based on Maunder and Culham (1997).

Ex situ conservation at its crudest may temporarily hold token samples of wild plant diversity. At best it can play a critical role as one component of an integrated conservation response supporting a primary objective: the retention and restoration of wild plant diversity. However, to achieve this objective, improved working practices and facilities are needed. We contend that it is because ex situ tools are not widely understood that they are undervalued and therefore underused. Understanding and effectively communicating the relative conservation roles, values, opportunities, and challenges faced by seed storage and growing collections may be among the biggest challenges practitioners face. A major purpose of this volume is to explore the value, limits, and range of available ex situ tools.

The Plant Diversity Crisis

The old World Conservation Union (IUCN) survey of plant species conservation status indicates that about 33,400 plant species are threatened with extinction (Walter and Gillett 1998), or about 10 percent of the world’s known 250,000–300,000 plant species. This IUCN survey records 380 plant extinctions (Walter and Gillett 1998), less than 1 percent of the recorded species of vascular plants. The plant extinctions recorded by the IUCN and World Conservation Monitoring Center (WCMC) reflect, in part, the geographic distribution of botanical knowledge and monitoring rather than actual rates of species loss. For the largest part of the planet there is no clear consensus on the rate of species and population loss, but this is improving as more IUCN Red Lists are undertaken. For example, in a review of recorded extinctions, rates of habitat conversion, and distribution of restricted endemic plant species for tropical Latin America, Koopowitz et al. (1994) produced estimates of recent extinctions that far exceed those the WCMC and IUCN record. This discrepancy is particularly notable for Brazil, where WCMC and IUCN recorded only five extinctions, whereas Koopowitz et al. estimate a loss since 1950 of about 2,200 species.

There is an acute need to act decisively, creatively, and effectively. Extinction rates for both species and populations are increasing as a result of human changes to habitats (Hannah et al. 1994; Hughes et al. 1997). This trend is accelerating as surviving wild areas become increasingly degraded through isolation, fragmentation, competition from invasive species, and climate change (Sala et al. 2000). The expected result, particularly in the endemic-rich hotspots (sensu Myers et al. 2000), will be many more plant extinctions.

The dearth of field survey work and the rapidity of habitat loss, particularly in the tropics, mean that many plant extinctions are likely to be identified only in retrospect, if at all. This raises the question, How should facilities, especially those in the high-diversity regions, most effectively allocate their limited resources? Should they focus a large proportion of their limited resources on managing a small number of threatened plant species, perhaps selected through an imperfect understanding of local conservation priorities? Or should they also use available resources for promoting and supporting the conservation of important habitat areas, such as recognized centers of plant diversity (Maunder et al. 2002; Chapter 5, this volume)? In addition to measuring yield from ex situ investment through increased taxonomic representation in cultivation or seed banks (e.g., scoring collections against national red lists), facilities could also score against quantitative assessments of genetic representation, contributions to implemented recovery plans, and the conservation of important plant habitats.

The Evolution of Ex Situ Plant Conservation

Botanic gardens, as scientifically organized plant collections, were originally initiated as repositories serving academic study, predominantly medical and theological (Prest 1981). In a time still dominated by an essentialist worldview dating back to Plato, curation was driven by the desire to accumulate typological specimens. They subsequently developed as resources for both colonial agriculture and taxonomic science (Osborne 1995; McCracken 1997). Only in the last 50 years of a 500-year post-Renaissance history have these collections and facilities been used to counter a human-mediated decline in species diversity. A specific ex situ conservation role could arguably develop only after the concept and reality of extinction, and in particular the role of humans in accelerating extinction rates, were first recognized and then accepted by the scientific community. Another foundational scientific advance that underlies current conservation thinking was the shift from an essentialistic, or typological, specimen-based approach to a populational view of the biological world (Mayr 1982). What it means to have a representative sample has profoundly changed. Rather than viewing individual differences as corrupt and imperfect manifestations of a Platonic ideal, biological variation has come to be appreciated as the raw material upon which natural selection acts and adaptive evolution depends. In other words, conservation of wild species as both a scientific and an ethical goal is a consequence of the revolution in late-eighteenth- and nineteenth-century scientific thought.

In the late nineteenth and early twentieth centuries two tree species were assumed to have become extinct in the wild and to have survived only in cultivation, namely Ginkgo biloba (Ginkgoaceae) from China (Wilson 1919) and Amherstia nobilis (Fabaceae) from Myanmar (Blatter and Millard 1993). These species, along with the U.S. endemic tree Franklinia alatamaha (Theaceae), appear to have been treated as isolated novelties and did not prompt a broad conservation response from the botanic garden community. The development of ex situ conservation reflected a cultural and scientific transition for plant collections from a focus on accumulating typological specimens as a curatorial goal to the adoption of population genetics as a working tool to conserve threatened