Botanical Gardens

M. Soderstrom , in Encyclopedia of Ecology, 2008

Gardens for Systematic Study

Botanic gardens are gardens where plants are gathered together for systematic study. Often they imitate a number of naturally occurring ecosystems: the San Francisco Botanical Garden has created a cloud forest section while the basement of the Palm House ( Figure 1 ) in the Royal Botanical Gardens at Kew ( Figure 2 ) features marine and intertidal habitats, for example. But in botanic gardens the term ecology means far more than imitation, and the gardens' ecological impact has changed as philosophies and world views have evolved.

Figure 1. The Palm House at Kew is one of its most distinctive features, and inspired many other glasshouses in other botanic gardens. Photograph by M. Soderstrom.

Figure 2. Bluebells growing under trees in the Conservation Area of The Royal Botanic Gardens at Kew. Photograph by M. Soderstrom.

Originally, interest was directed toward collecting and studying plants themselves, with little care taken in recording details of the plants' habitats or in safeguarding the ecosystems. Later, during the period of what might be called the imperial botanic garden, Western countries used botanic gardens to transfer plants from one part of the world to another, with sometimes devastating consequences for the ecosystems receiving the foreign plants. Most recently, botanic gardens have begun to play a major role in conserving endangered plants and preserving threatened habitats. Nearly 2500 botanic gardens are listed with Botanic Gardens Conservation International. To search for gardens by country, refer to http://www.bgci.org.uk/. Table 1 lists a few selected gardens.

Table 1. Selected botanic gardens

Early botanical gardens
Orto Botanico at Pisa, Italy: founded c. 1545
Orto Botanico at Padua, Italy: founded c. 1545
Hortus Botanicus, Leiden, Netherlands: founded 1590
Le Jardin des plantes de la Université Montpellier, France: founded 1593
Oxford Physic Garden, Oxford University, UK: founded 1621
Le Jardin des plantes, Paris, France: founded 1626
Some other notable European gardens
Botanischer Garten und Botanisches Museum Berlin-Dahlem, Berlin, Germany
Linnaean Garden, Botaniska trädgården, Uppsala, Sweden
Jardín Botánico de Madrid, Spain
Jardim Botanico, University of Coimbra, Portugal
The Royal Botanic Gardens at Kew, London, UK
The Royal Botanic Garden, Edinburgh, Scotland
Eden Project, Cornwall UK
The National Botanic Garden of Wales, Llanarthne, Carmarthenshire, Wales, UK
Some gardens with colonial roots
Amani Nature Reserve, Tanzania
Bogor Botanical Gardens, Bogor, Indonesia
Indian Botanical Gardens, Shibpur, Kolkata, India
Pamplemousse Botanic Gardens, Mauritius
Rimba Ilmu Botanic Gardens, Kuala Lumpur, Malaysia
Royal Botanic Gardens, Trinidad
Singapore Botanic Gardens, Singapore
Some notable New World gardens
USA
  Boyce Thompson Arboretum. Superior, AZ
  Brooklyn Botanic Garden, New York
  Chicago Botanic Garden, Chicago, IL
  Fairchild Tropical Botanic Garden, Fairchild, FL
  Hawaii Tropical Botanical Garden, outside Hilo, Hawaii
  Missouri Botanical Garden, St. Louis, MO
  New York Botancial Gardens, New York
  San Francisco Botanical Garden at Strybing Arboretum, CA
Canada
  Jardin botanique, Montréal, QC
  Royal Botanical Gardens, Hamilton, OM
  UBC Botanical Garden and Centre for Plant Research, Vancouver, BC
Latin America
  Belize Botanic Garden, San Ignacio, Belize
  Jardin Botanico Francisco Javier Clavijero, Xalapa, Veracruz, Mexico
  The UNAM Botanical Garden, Mexico City, Mexico
  Jardim Botânico de São Paulo – São Paulo, Brazil
  Jardim Botânico do Rio de Janeiro – Rio de Janeiro, Brazil
Some Asian gardens
Maharashtra (Mahim) Nature Park in Mumbai, India
Narayana Gurukula Botanical Sanctuary, North Wayanad, Kerala, India
Beijing Botanical Garden, Beijing, China
Lijiang Botanic Garden & Research Station, Yunnan Province, China
Nanjing Botanical Garden, Nanjing, China
Koishikawa Botanical Gardens, Tokyo, Japan
Some Southern Hemisphere gardens
Kirstenbosch National Botanical Garden, Cape Town, South Africa
Royal Botanic Gardens – Melbourne, Victoria, Australia
Royal Botanic Gardens – Sydney, New South Wales, Australia
Alice Springs Desert Park and Olive Pink Botanic Garden, Northern Territory, Australia
Bafut Botanic Garden in northwest Cameroon

According to Botanic Garden Conservation International, at the beginning of the twenty-first century some 2000 botanic gardens in 148 countries harbored representatives of more than 80   000 plant species, or about one-third of the vascular plant species in the world. The gardens range from large ones like Kew and the New York Botanical Garden, where gorgeous plant displays are coupled with scientific research, to much smaller ones like Nezahat Gokyigit Memorial Park, near Istanbul, Turkey and Bafut Botanic Garden in northwest Cameroon which concentrate on safeguarding and studying local biosystems.

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In Situ, Ex Situ Conservation

Nigel Maxted , in Encyclopedia of Biodiversity (Second Edition), 2013

Botanical/Zoological Garden Conservation

Historically, botanical or zoological gardens were often associated with physic or medicinal gardens or displays of single specimens of zoological curiosities, and as such they did not attempt to reflect the genetic diversity of the species. These gardens now hold living collections of species that were collected in a particular location and moved to the garden to be conserved. The advantage of this method is that gardens do not have the same constraints as many other conservation agencies; they have the freedom to focus on wild species that may otherwise not be given sufficient priority for conservation. Yet there are two disadvantages to this technique. The first is that the number of species that can be genetically conserved in a botanical or zoological garden will always be limited because of the available space. The majority of these gardens are located in urban areas in temperate countries, and at their present sites most expansion would be prohibitively expensive. The majority of botanical and animal diversity is located in tropical climates, yet because most botanical and zoological gardens are in temperate countries, the collections must be kept in expensive greenhouses or other facilities, which also limits the space available. The second disadvantage is related to the first, namely very few individuals of each species can be held, and this severely restricts the range of genetic diversity found in the wild that is protected. However, if the target species is very near extinction and only one or two specimens remain extant, this objection of course does not hold.

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THE CONSERVATION OF AQUATIC RESOURCES THROUGH MANAGEMENT OF GENETIC RISKS

In Conservation of Fish and Shellfish Resources, 1995

Living Collections

The best known example of living collections are zoological and botanical gardens, fish hatcheries, and aquaria. Many living collections have been developed for research, education, or display purposes. Living collections can also be a useful way to preserve genetic material, including maintaining breeding stocks of populations threatened in the wild.

Living collections require intensive breeding management. With judicious breeding management, collections can limit the amount of inbreeding and random genetic drift relative to that which would occur in small, unmanaged populations. For this reason living collections are an attractive alternative for preserving extremely scarce genetic resources.

Living collections can maintain genetic materials that cannot be stored in gene banks. Currently, technologies for long-term storage of ova or embryos do not exist for many species of aquatic organisms. Consequently the maintenance of living collections is the only controllable alternative for the genetic conservation of some aquatic species, especially viviparous and ovoviviparous species.

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Museums and Institutions, Role of

Michael J. Novacek , Suzann L. Goldberg , in Encyclopedia of Biodiversity (Second Edition), 2013

Eliciting Public Understanding and Engagement

Beyond advanced academic training and school programs, museums, botanical gardens, and related institutions have a unique connection with a vast public audience. Even in more economically and technologically advanced countries, there are limited opportunities for the lay public to stay abreast of the rapid rate of scientific discovery ( Falk et al., 2007). Outside popular science books, periodicals, films, television specials, and web offerings, the responsibility for providing a lifelong exposure to science falls to museums, botanical gardens, zoos, aquaria, science centers, and similar venues devoted to the public education of science.

These institutions are thus critically important in educating people on biodiversity issues and other environmental problems. However, in doing so they confront some major challenges. A consistent result in surveys of public attitudes, such as the Biodiversity Roadmap Report of 1998, is that the basic message – that the biodiversity enormously important to the sustainability of the environment and the quality of our own lives is at serious risk – is not getting across to many of the target audiences. The most penetrating messages are those that clearly relate scientific insights concerning biodiversity and biodiversity loss to more general environmental problems and in turn to problems rooted in common experience – poor water quality, depletion of fisheries, zebra mussels and other invasive species, forest clearing, open pit mining, urban sprawl, and many others. Basic biodiversity science of course provides the important database for all these arguments. But the public recognition of the importance of this work is elusive without the themes that address more familiar issues (Novacek, 2008).

One bridge that must be crossed in connecting biodiversity science with a diverse public is in inspiring a closer interest in and affinity with nature. The fact that museums and like institutions can offer an encounter with nature that is both vivid and authentic defines their cultural impact (Novacek, 2001). Many people, especially in urban areas, will rarely, if ever, see a relatively unspoiled tract of woodland in their region, let alone a tropical rainforest. For these individuals, an encounter with nature means a visit to a museum or the like. The enthusiastic response of visitors to this opportunity can be appreciated in terms of the huge audiences such institutions attract. Attendance figures for 2010 provided on the websites of just 18 museums, botanical gardens, zoos, and aquaria, including some of those shown in Figures 1 and 2, numbered more than 44 million visitors. Another survey claimed that more than 865 million people visited museums, gardens, zoos, nature centers, science centers, and related venues in 1999 in the USA alone (Lake and Perry and Associates, 2001). An additional attribute of museums and institutions as venues for communicating science is the feeling of trust they invoke in the public. Surveys show that natural history and science museums have extremely high credibility ratings (Lake and Perry and Associates, 2001).

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Biodiversity

S. Volis , in Encyclopedia of the Anthropocene, 2018

Role of Ex Situ Conservation: Living Collections in Botanical Gardens

The major depositories for living plants representing threatened species traditionally are botanical gardens and arboreta. These collections' aim is to serve a germplasm backup in a case of in situ conservation failure, preserve the species genetic diversity, and help propagating germplasm for in situ actions ( Prance, 1997; Maunder et al., 2001; IPGRI, 2004; Guerrant et al., 2004). However, role of botanical gardens and arboreta in conservation should not be overestimated due to numerous limitations in their utility for maintaining sufficiently large and genetically diverse living collections. Some of the problems are associated with poor genetic or demographic management, for example, mislabeling, representation of species by only a few individuals, and lack of information on accession sampling locality. When the number of stored accessions per species is low or they are inadequately documented or mixed, these collections are extremely vulnerable to the processes of genetic erosion, artificial selection, and infestation by pathogens. Physical proximity of plants having different origin can lead to spontaneous hybridization with produced offspring lacking genetic integrity and having maladaptive gene combinations. To prevent or at least reduce these effects, sampled individuals must be maintained separately or through controlled breeding and pedigree design. This introduces two major weaknesses of botanic garden and arboreta ex situ collections—their low capacity and high cost of maintenance. As a result, in overwhelming majority of the cases, the garden living collections are far from what is needed to represent the species genetic diversity (e.g., 10–50 individual plants from five natural populations). The above problems and weaknesses of living collections in gardens and arboreta call for reevaluation of their specific tasks. The goals of serving a germplasm depository properly preserving the species genetic diversity and providing material for in situ actions appear to be too ambitious for these collections given their limited space and financial resources. Instead, their role should be limited largely to botanical research, development of seed germination, cutting and tissue culture propagation techniques, and education. The above conservation goals can be achieved only by a strategy that is specifically designed to integrate ex situ and in situ conservation components and is less space limited and much cheaper.

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ROSE COLLECTIONS AND TRIALS | Rose Collections and Herbaria

T. Cairns , in Encyclopedia of Rose Science, 2003

Czech Republic

Rosarium, Exhibition Grounds FLORA Olomouc

Olomouc, Wolkerova

Founded in 1972 with the assistance of the Rosa Club, a botanical garden setting with about 300 cultivars (plus a strong representation of roses from Czech breeders) on 3.4  ha. Best viewed in the middle of June.

Rosarium, Institute of Botany, Czech Academy of Science

Pruhonice, near Prague

A 250-ha natural park dating back to 1885 with a rose garden begun in 1964 by Prof. Svoboda. Managed by the Institute of Botany, it has approx. 600 modern roses and 210 historical roses, co-located with the Research Institute of Decorative Horticulture. A showcase setting for roses from Czech hybridizers.

Rosarium, International Contest of Rose Novelties

Hradec Králové-Kukleny Pardubicka

Established in 1974, it is home to an outstanding Annual International Rose Trials with an attractive rose garden featuring about 100 varieties. Best viewed in the middle of June.

Rosarium and Rose Garden of Prague

Hill Petrin, Prague

Founded in 1932, both these gardens are situated on the remains of the medieval fortifications of Prague. There are approx. 2000 rose bushes. Best viewed in the middle of June.

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Education and Biodiversity

Shirley M. Malcom , in Encyclopedia of Biodiversity, 2001

IV.B. Zoos and Other "Places of Science"

Animal parks were established by and for rulers. Maier and Page, in their volume Zoo: The Modern Ark (1990), describe how animals were kept by royalty for entertainment and as a show of wealth. The third dynasty ruler of the Sumerian city of Ur had a park that dated around 2300 B.C. A millennium later as civilization spread in the Near East and Asia, rulers and pharaohs exchanged "exotic" animals for their zoos. Emperor Wu Wang of the Chou dynasty laid out a zoological garden called the Park of Intelligence. Animal collections were found around the globe in early civilizations such as in Egypt some 3500 years ago.

Alexander the Great, perhaps influenced by Aristotle's private menagerie, installed what was perhaps the first public zoo in Alexandria, Egypt.

With the coming of the "Dark Ages" of Europe, monasteries became the keepers of menageries and game parks. When Cortes arrived in the Aztec capital of Tenochtitlan, he found a large zoo behind Emperor Montezuma's palace. Zoos in India were established by Akbar toward the end of the 16th/ century. He, like the Aztecs, employed people specially trained to care for and medically tend to animals.

The zoo at Vienna was reinvigorated by Maria Theresa and her husband as the Imperial Menagerie at Schönbrun for the convenience and entertainment of the nobility. The zoo remains today as likely the oldest in continuous operation, dating from the 1750s.

Democratization of Europe and establishment of urban centers that accompanied industrialization led to the "modern zoo" as a repository of exotic specimens of life that were to be studied as a way of understanding "flora and fauna" of the world. Public monies (rather than private patrons or royal largesse) were available to begin systematic scholarly study. Maier and Page date the modern zoo to 1826 when the Zoological Society of London founded the zoological gardens at Regent's Park for the purpose of understanding the natural history of the animals inhabiting the reaches of the British Empire.

Since zoos as public institutions had to raise funds and attract money (independent of their research and conservation goals), they had to become popular attractions. Zoo organizers also had to learn to manage space and figure out and meet animals' requirements, such as for social interaction. Zoos' role in conservation became educational as they raised visitor awareness about endangered species and loss of habitat. Where larger zoos also developed significant breeding herds, they established breeding farms. In San Diego, for example, this "wild animal park" has become an additional attraction.

The National Zoological Park (National Zoo), associated with the Smithsonian Institution, established a "biopark," Amazonia, to emphasize the relationships among soil, plant, invertebrate, and other animal forms and the need to preserve the habitats of the world. Zoos, aquariums, and game parks are being seen as tools to affect public attitudes regarding the variety of life on earth.

As these "places of science" intentionally blend education and entertainment they are increasingly adding materials from museum collections and incorporating interactive exhibits from science—technology centers to reinforce conservation messages, concern about loss of species numbers, and diversity and loss of habitat.

IV.B.1. Botanical Gardens

In 1989 the World Resources Institute estimated that 150 million persons visited some 1500 botanical gardens around the world. In addition to visits and guided tours, gardens offered continuing education for adults, workshops and hands-on experiences for children and families, and professional education courses and seminars for K–12 teachers. The New York Botanical Garden and Missouri Botanical Garden are examples of two of 21 member gardens of the American Association of Botanical Gardens and Arboreta offering graduate studies programs, usually in collaboration with universities in their area.

IV.B.2. Museums

Through collections, education programs, exhibitions, and graduate-level research, museums have been very active in promoting biodiversity in both the formal and informal sectors. The American Museum of Natural History in New York (AMNH) provides an interesting example of an institution with current involvement in all these areas:

•

Exhibition. The 11,000-square-foot Hall of Biodiversity is the newest permanent exhibit of AMNH and uses collections, interactive technologies, and an immersive environmental replica of a portion of the rain forest of the Central African Republic—complete with sound, smell, movement, and running water—to provide a unique visitor experience.

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Graduate and continuing education. The Center for Biodiversity and Conservation collaborates within and outside the museum in the development of courses and programs. AMNH is home to the oldest and largest doctoral and postdoctoral training program of any scientific museum in the world, collaborating with Yale, Columbia, Cornell, and City University of New York.

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Education. The National Center for Science Literacy, Education and Technology supported by the National Aeronautics and Space Administration (NASA) has developed a number of projects related to the theme of biodiversity, including Biodiversity Counts: A Student Inventory Project, a program for middle school students across the United States to inventory plant and animal life in their communities and to share their findings through publications and on-line field journals.

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Plant Invasions

David M. Richardson , Petr Pyšek , in Encyclopedia of Biodiversity (Second Edition), 2013

Dispersal to a New Area

Important reasons for the intentional widespread translocation of plants include agriculture, forestry and agroforestry, botanical gardens, horticulture (including the commercial trade in seeds, bulbs, and cuttings, and urban gardeners using seed exchanges), and soil stabilization. Many plants have been moved around the world inadvertently, notably in ship ballast, with military transport, and as contaminants in fertilizers, hay and straw, grains, wool, and cotton. For the 622 woody invasive plants listed in a recent global review, those introduced for horticulture were most numerous (62% of species: 196 trees, 187 shrubs), followed by species introduced for forestry (13%), food (10%), and agroforestry (7%) ( Richardson and Rejmánek, 2011). In Europe, 62.8% of all currently naturalized aliens were intentionally introduced. Ornamentals and escapees from horticulture account for the highest number of species (52.2%). Among accidental introductions, contaminants of seed, mineral materials and other commodities are responsible for 1091 alien species introductions to Europe (76.6% of all species introduced unintentionally) and 363 species are assumed to have arrived as stowaways (directly associated with human transport but arriving independently of commodity) (Lambdon et al., 2008).

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Plant Invasions

David M. Richardson , in Encyclopedia of Biodiversity, 2001

IV. Invasion Processes

Plant invasions in natural and seminatural ecosystems involve the following fundamental phases: introduction to the region by humans, establishment, population growth (sometimes accompanied by genetic adjustment), spread to new areas within the region (and often also outside the region via further dispersal by humans; see Fig. 2), interaction with the local biota and disturbance regime, and displacement of native elements. There are many ways of conceptualizing the various processes involved in invasion and interactions with biotic and abiotic features of the new environment. One may depict the various potentially limiting factors as a series of "barriers." The simplest representation of such a model shows (a) a geographic barrier, which must be overcome by dispersal; (b) a habitat barrier, which requires preadaptation or genetic adjustment to the conditions of the new environment; and (c) a biotic barrier, which integrates the forces of predation, herbivory, competition, and interference that must be overcome in the new habitat, or the new mutualistic relationships that must develop. Additional complexity can be added by, for example, splitting the geographic barrier into two components (to account for factors limiting introduction to the region and dispersal within the region, respectively), by adding a reproductive barrier (to account specifically for factors that potentially limit seed set), or by splitting the biotic barrier into components (e.g., to isolate the role of mutualisms) (Fig. 3).

Figure 3. A schematic representation of major barriers limiting the invasion of introduced plants. The barriers are (A) geographic barrier I: Intercontinental or international and/or infracontinental; (B) reproductive barrier; (C) physical and chemical environmental barrier(s); (D) geographic barrier II (within the new region); (E) biotic barrier(s) I (general composition of fauna and flora); (F) biotic barriers(s) II (successionally mature, undisturbed plant communities). In many cases, alien plants establish mutualisms with other organisms to enable them to overcome barriers. For example, pollination (barrier B) and seed dispersal (D) by animals are often essential for invasion. Ants bury the seeds of some introduced plants, thus protecting them against predation and fire (barriers E and F). Many introduced plants fail in the absence of mycorrhizal fungi or nitrogen-fixing bacteria (barriers C, E, and F).

IV.A. Stages of Invasion

IV.A.1. Dispersal to a New Area

Important reasons for the intentional widespread translocation of plants include agriculture and forestry and agroforestry, botanical gardens, horticulture (including the commercial trade in seeds, bulbs, and cuttings and urban gardeners using seed exchanges), and soil stabilization. Many plants have been moved around the world inadvertently, notably in ship ballast, with military transport, and as contaminants in fertilizers, hay and straw, grains, wool, and cotton.

IV.A.2. Establishment and Naturalization

Empirical evidence shows that the chance of becoming established, naturalized, and later invasive increases markedly with an increase in the number of propagules introduced, and with multiple introductions (including introductions at different times and from different source populations). More propagules reduce the likelihood of extinction and increase the chance of longdistance dispersal. Multiple introductions allow the incipient invader to sample a greater range of sites over space and time in the new environment and (since different introductions often originate from different source populations) improve the likelihood of introducing a genotype closely suited to local conditions. Also, multiple introductions increase the likelihood of forming novel genotypes that facilitate invasion. Successful establishment entails dealing with numerous physical, chemical, and biotic barriers (Fig. 3). Many introduced plants are initially grown in small populations that are inherently susceptible to extinction due to chance events. To establish and persist, a population must exhibit dN/dt > 0 when N is small (the "invasion criterion"). If an introduced plant can deal with various reproductive barriers, it becomes naturalized.

IV.A.3. Spread

Invasion involves dispersal within the new area and population growth. Invasive alien floras show a wide range of adaptations for dispersal. Many species are dispersed by "passive" agents such as water or wind. A large proportion of the world's most widespread and damaging invaders are dispersed by birds and mammals (both native and introduced). The rapidity with which these mutualistic seed-dispersal interactions establish suggests that vertebrate-dispersed plants have converged into generalized dispersal syndromes regardless of phylogenetic and geographical origins. Epizoochorous dispersal, mainly by cattle and sheep, facilitates the spread of many (mainly herbaceous) invaders. Vegetative reproduction is also important.

The dynamics of range expansion and population growth of an invasive alien plant typically follow the pattern shown in Fig. 4. There is frequently a time lag between the arrival of an alien plant in a new habitat and the start of widespread invasion. Examples include Thlaspi caerulescens (Brassicaceae), which was cultivated at Oslo Botanical Garden in Norway since 1814, was first collected as an escapee in 1874, spread slowly until 1900, then expanded rapidly until it reached most of its present range in about 1945; Mimosa pigra (Fabaceae), which was virtually confined to small areas around Darwin in Australia for 80 years before exploding; and Melaleuca quinquenervia (Myrtaceae), which showed no invasive tendencies for its first 50 years in Florida (United States). A recent analysis of the history of woody species introduced to Brandenburg in Germany revealed an average time lag between introduction and invasive spread of 147 years (170 years for trees; 131 for shrubs)! Such lags, frequently alluded to but very seldom adequately explained in the invasion literature, are probably usually due to one or more of the following factors: (a) the founder population may maintain a stable, small population until genetic adjustment occurs or essential mutualists (seed dispersers, pollinators, mycorrhizal fungi) arrive (the extent of genetic alteration preceding or accompanying invasion has been studied for a few widespread invaders, e.g. Ailanthus altissima in the United States); (b) some lags are probably explained by an initial shortage of "safe sites," which have become more abundant as human-induced disruption of ecosystems has increased (increasing time also improves the chance of a potential invader encountering a "safe site" formed by a rare event such as a flood); (c) populations spread slowly at their periphery but only show accelerated growth rates when there are many foci of growth.

Figure 4. Model of the spread of an invasive alien plant over time. From Hobbs and Humphries (1995).

The lag phase is followed by a phase of sudden growth during which populations increase at an exponential rate (and generally become noticed as invaders). One reason for the increased growth rate (besides those mentioned earlier that may prevent its realization) is the typical two-phase pattern of spatial expansion. This involves the densest recruitment of offspring close to founder populations ("neighborhood diffusion") and the establishment of isolated colonists through longdistance dispersal. As satellite foci grow in size through diffusion, often coalescing with each other and the founder metapopulation, more propagules become available for additional jump dispersal. With increasing numbers of growth foci, population growth and range increase rapidly. The rate of spread is frequently augmented by intentional or accidental movement of plants within the invasion arena by humans, thus creating additional nascent foci. This process, termed "stratified diffusion," has been documented for many plant invasions involving disparate plant taxa and environments and is evident at scales ranging from global (Fig. 2), regional, to landscape (Fig. 5). The end of the exponential phase usually occurs when most optimum sites for invasion are occupied (or when successful control is instituted). Alien plant invasions may also follow linear trajectories (e.g., in the case of spread along rivers or coastal foredunes). Invasions in these habitats usually proceed as a wave front.

Figure 5. The simulated spread of alien pine trees in South African fynbos over 100 years in an area of 1.5   km × 1.5   km to illustrate the process of stratified diffusion. All simulations start with 75 plants; A shows spread from the edge of a plantation (at bottom left); B shows spread from a clump in the center; and C shows spread from plants randomly arranged across the invasion arena. White pixels show areas occupied by invading pines; black areas are free of pines. Details of the modeling procedure are described in Higgins and Richardson (1998).

Spread rates reported for invasive alien plants vary greatly. Some examples are 5000   m yr−1 for Bromus tectorum (Poaceae) in North America; 4000 to 13,000   m yr−1 for Heterotheca latifolia (Asteraceae) in the Georgia piedmont; 970   m   yr−1 for Fraxinus ornus (Oleaceae) along a river in France; 76   m   yr−1 for Mimosa pigra (Fabaceae) in wetlands in northern Australia; 21 to 31   m   yr−1 for Acacia cyclops (Fabaceae) and Pinus pinaster (Pinaceae) in South African fynbos; and 14   m yr−1 for Ammophila arenaria (marram grass; Poaceae) on coastal dunes in California.

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Biodiversity

J.A. McNeely , in Encyclopedia of the Anthropocene, 2018

Article 9: Ex Situ Conservation

Conservation of components of biodiversity in natural habitats can be complemented by some activities in zoos, botanical gardens, game ranches, laboratories, and other such settings (labeled ex situ conservation). This article calls for establishing and maintaining facilities for ex situ conservation, including research, on plants, animals, and micro-organisms (preferably in the country of origin of these genetic resources). Parties are also expected to adopt measures for the recovery and rehabilitation of threatened species, leading to the reintroduction of such species into their natural habitats when this is appropriate. The ranching in southern Africa of White Rhinoceros and Black Rhinoceros provides a good example of putting this measure into practice, though it is not always safe for the rhinos to do so; poaching still happens on private ranches. Where species are under serious threat, collecting for ex situ conservation purposes should be managed so that the wild populations are not further threatened, except when temporary measures are required to conserve them as a basis for subsequent re-introduction (as with the Giant Salamander in China and other amphibians in many parts of the world).

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