Introduction: challenges and opportunities

Botanic gardens face both challenges and opportunities in responding to global and, in particular, climate change (Tables 1 and 2). Firstly, they will have to reassess their accessions policies as the growing conditions in the predicted new climatic envelopes for some, if not many, of the plants currently cultivated will no longer be suitable for them. Secondly, the increased numbers of species put at risk as a result of the changing climatic conditions will force them to refocus and strengthen their conservation policies and increase their participation in recovery programmes for critically endangered species. Thirdly, botanic gardens will face an unprecedented opportunity to develop their role as introduction centres and play a major role in the assessment of new germplasm both of ornamentals as well as other economically important plants. These three challenges are interrelated to some extent but this paper focuses on the third one and outlines the issues involved in adopting or reinforcing the introduction and resource role of botanic gardens.

Table 1 Challenges faced by botanic gardens in response to climate change
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Table 2 Opportunities for botanic gardens in response to climate change
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The plant introduction process

Plant introduction has a long history, dating back thousands of years (Del Tredici 2000) and has been practised by various civilizations and cultures, ranging from the ancient Chinese, Egyptians, Greeks and Romans through major episodes such as the post-Columbian period and the five main waves of mainly ornamental plant introduction since the sixteenth century (Stuart 2002) to the present day. Most civilizations have engaged in a two-way traffic of introduction and export of plant (and to a lesser extent animal) resources. Exploration and the introduction of plants into cultivation has been a major underpinning of agriculture, horticulture, trade and socio-economic development over the centuries. As noted in the St Louis Declaration (2002) ‘Plant introduction and improvement are the foundation of modern agriculture, yielding diversity to our supply of plants used for food, forestry, landscapes and gardens, and other purposes’. As Thomas Jefferson famously said, ‘The greatest service which can be rendered to any country is to add a useful plant to its culture’. He also wrote in a letter to M. Giraud (1797) ‘I received the seeds of the bread tree… One service of this kind rendered to a nation, is worth more to them than all the victories of the most splendid pages of their history, and becomes a source of exalted pleasure to those who have been instrumental in it’. Plant introduction has been driven by commercial, scientific, medicinal and even personal goals (Ward 2004). The specific reasons for introducing plants are diverse and include scientific curiosity, biophilia, collections, medicinal potential, trade (such as in spices), agriculture, forestry, gardening, ornamental horticulture, and community benefit and social use (Heywood 2006).

The impacts of plant introduction have been far-reaching and have been a major driver in population growth and economic development in some cases. For example, the main impact of New World introductions in Europe and the Mediterranean was on the nutritional balance of the agricultural economy, with maize (Zea mays), potatoes (Solanum tuberosum) and beans (Phaseolus) producing many more calories per hectare than the traditional arable crops of pre-columbian agriculture such as wheat and barley. The introduction of crops with higher calorific value had a marked impact on demography, with the increased agricultural productivity allowing substantial population growth and consequent development (Malanima 2006).

The acquisition and introduction of new crops was almost a defining characteristic of the colonization process by the European powers as Calestous Juma notes in The Gene Hunters (1989): ‘…the acquisition of colonies was not enough unless linked with the availability of labour and plant genetic resources’. This involved the movement of stocks of economically useful plants from one part of the world to another on a massive scale in the furtherance of colonial agriculture. The combined networks of colonial botanic gardens served as a very effective mechanism for the transfer of germplasm around the world, long before the modern genetic resources movement was developed.

The initial focus of introductions was on plants that could add to the agricultural wealth of the country or those of medicinal value although ornamentals were also included and interest in these grew as gardening gradually became a leisure pursuit with the increase in wealth. The actual process of plant introduction is however poorly circumscribed and ranges from almost casual plant collecting to well organized and structured approaches (Ault 2000). The actors are likewise many and varied and have included travellers, explorers, field botanists, diplomats, surgeons, sea captains, civil servants, nursery owners, landowners, gardeners, and of course the celebrated professional plant collectors such as John Tradescant, John Bartram, Charles Curtis, David Fairchild, Francis Masson, Ernest Wilson, George Forest, David Douglas, Frank Meyer, Reginald Farrer, Robert Fortune, William and Thomas Lobb, Richard Spruce, John Gould Veitch who were responsible for bringing into cultivation many of our best known garden plants and trees (Gribben and Gribben 2008). An account of recent plant collectors is given by Ward (2004).

Responsibility for introductions gradually transferred to agricultural stations or Departments of Agriculture and some of the collectors were sponsored by official institutions, as in the United States where the renowned plant explorer David Fairchild had the splendid title of ‘Agricultural Explorer, in Charge of Foreign Explorations’.Footnote 1 Another important figure was Frank Meyer, regarded as the doyen of agricultural explorers, who was employed by the US Department of Agriculture and from 1905 to 1918 was responsible for thousands of introductions from China to other parts of eastern Asia (Cunningham 1984; Kaplan 1998).

The basic procedures of plant introduction have remained largely unchanged over the past 400 years and it often is difficult to discern any general coherent policy lines. In fact, despite its acknowledged importance, plant introduction, with a few exceptions, has been described as largely a random, poorly organized, insufficiently collaborative, badly publicized and inefficiently followed through process. Yet it could be argued that it has been remarkably successful in the sense that tens of thousands of species have been brought into cultivation. In Europe alone, about 17,000 taxa (12,000 species plus subspecies, varieties and hybrids) are grown in gardens (European Garden Flora Editorial Committee 1984–2000).

Botanic gardens as introduction centres

Historically, many botanic gardens, especially those located in the tropics, have acted as plant introduction centres and played a major role in the spread of germplasm of agricultural, industrial, forestry and ornamental plants around the world. Their actions in helping establish the agricultural economies in several parts of the tropics and subtropics through the introduction of plantation crops such as coffee, tea, oil palm and rubber have been well documented (Brockway 1979; Heywood 1985; Holttum 1970; Purseglove 1959). Such actions were not confined to gardens such as Bogor (Indonesia), Howrah (India), Peradeniya (Sri Lanka), Pamplemousses (Mauritius) and Singapore but involved many other botanic gardens in tropical Asia, such as the Lalbagh Botanical Garden, Bangalore (India) and, the Caribbean such as the St Vincent Botanic Garden (Windward Islands) and the Bath Botanical Garden (Jamaica).

Lalbagh Botanical Garden, Bangalore, although dating from 1760, for over 150 years has been the hub of the horticultural trade and industry in the state of Karnataka since it became the State Botanical Garden in 1856. The first botanic garden in the New World tropicsFootnote 2 was established in 1765 on St Vincent in the West Indies, promoted by the Royal Society of London. This garden which persists to the present day was instrumental in introducing breadfruit as cheap food for the slaves in much the same way as Pamplemousses did for cassava (Manihot esculenta). Other germplasm resources developed at St Vincent included nutmeg (Myristica sp.), arrowroot (Maranta arundinacea) and the celebrated sea island cotton (Gossypium barbadense) cultivars. The reputation of the St Vincent Botanic Garden as an acclimatization garden for the whole of the West Indies was influential in persuading the East India Company to go ahead and establish the garden at Calcutta. There the Indian (formerly Royal Botanic) Garden was originally envisaged by its founder Lt Col. Robert Kyd, the Military Secretary to the Government in India, as a trial garden to grow a range of useful crops such as Sago palm (Cycas revoluta) and Persian date palm (Phoenix dactylifera) as sources of nutritious food for the native population, and of teak (Tectona sp.), spices, tea (Camellia sinensis) and coffee (Coffea sp.) for trade.

The French involvement in tropical germplasm introduction followed a different pattern, the key central institution being the Muséum National d’Histoire Naturelle where the holder of the Chaire des Cultures, André Thouin, was responsible for introducing vanilla (Vanilla planifolia) from Mexico where it was grown by the pre-Hispanic cultures, to the Jardin de la Compagnie (the French East Indies Company) on the Island of Réunion from where it spread to other Indian Ocean islands. The Jardin des Plantes in Paris received seedlings of coffee from Amsterdam as part of the complex saga of the introduction of this crop to various parts of the world, in this case the neotropics.

These tropical botanic gardens were victims of their own success and led to the establishment of agricultural research stations and departments, thus leaving them without their main role which consequently led in many cases to their decline or closure. With the exception of ornamental plants, the involvement of botanic gardens in plant introduction largely disappeared following the creation of agricultural stations and centres in early twentieth century.

In the twentieth century, a number of gardens were opened in Italy for the introduction of plants from the colonies and in North Africa, the Jardin d’Essai, Rabat (Morocco) which opened officially in 1928 was an experimental garden that undertook trials on fruit trees and ornamental species. It fell into disrepair but plans for its major rehabilitation were announced in January 2009. An earlier foundation is the Jardin d’Essai du Hamma of Algiers, established under French rule in 1830, re-opened in May 2009 after 5 years of restoration work. Another North African garden that was of major importance for plant introductions is the experimental garden of El Saff about 50 km south of Cairo. A catalogue of the 2,000 species grown there was published by Bircher (1960). Also in Egypt were the experimental gardens of Zohriya (today the Zohira Trial Gardens) Gezireh west of Cairo, in which Delchevalerie (1870) established the first station for acclimatization of plants and where special attention was paid for propagation of tropical fruits such as the breadfruit tree (Artocarpus altilis), the sapodilla plum (Manilkara achras) and the mango (Mangifera indica) (Hamdy et al. 2007) An account of the flora of this garden was published by Delchevalerie (1871) with an update by Bircher (1998).

Mention must also be made of the remarkable plant introduction work carried out by Vavilov and the Institute of Plant Industry (Loskutov 1999) although the focus was mainly on new varieties of crops and did not involve many botanic gardens, an exception being the Nikita Botanical Garden which he said was in essence an agricultural establishment (Vavolov 1992, p. 446).

Botanic gardens and plant introduction today

In recent decades, with an increasing emphasis on conservation activities, plant introduction has not been a major concern of most botanic gardens and has tended to be overshadowed by the work of other institutions or commercial undertakings. Those gardens that are engaged in plant introduction today tend to direct most of their efforts at plants of horticultural merit as in the case of North American botanic gardens and arboreta such as the US National Arboretum, University of British Columbia Botanical Garden, and the consortium of six major botanic gardens and arboreta which form the Plant Collecting Collaborative, although expeditions organized by these gardens also provide plants of other interest, such as medicinal plants for study by ethnobotanists, rare and endangered plants studied for conservation purposes and food plants. The University of British Columbia Botanical Garden Plant Introduction Scheme (PISBG) has been introducing and recommending plants since 1985.Footnote 3 In Europe, the Barcelona Botanic Garden is experimenting with plants new to the Mediterranean climate with a view to their later introduction into gardening. In 2000 an agreement was made between the city council and municipalities in the metropolitan area to maintain the Garden and enable the centre to experiment with new plants and methods to promote sustainable gardening.Footnote 4

In some countries, a number of botanic gardens still include the introduction of agricultural, medicinal or other economically important plants as a significant part of their mission today. For example, many of Russia’s 80 botanic gardens are plant introduction centres to a greater or lesser degree (Gorbunov 2001). The rich collections of economic plants in botanic gardens are a good basis for applied research which has always been an important part of the activity of Russian botanic gardens. For example, experimental nurseries of aromatic plants were established in some central regions of Russia and the Botanic Garden of the Komi Institute of Biology in Syktyvkar is involved in prospecting for new forage crops in the north of Russia, where it has successfully introduced high yielding cultivars of Sosnowski's hogweed (Heracleum sosnovskii), white knotweed (Polygonum weirichii), radish (Rhaphanus sativus) and comfrey (Symphytum spp.). The Central Siberian Botanic Garden, Novosibirsk, is engaged in developing local native plant resources, food and forage plants and cultivars of forage crops with high protein content (Krasnoborov 1998). Botanic gardens in Russia have played a significant role in the introduction of such species as magnolia vine (Schizandra chinensis), Chinese gooseberry (Actinidia kolomikta), sea buckthorn (Hippophae rhamnoides), Nanking cherry (Cerasus tomentosa), gumi (Elaeagnus multiflora) and species and hybrids of rowan (Sorbus), roses (Rosa), honeysuckles (Lonicera), and blueberry (Vaccinium). The Botanic Garden of Moscow State University has introduced more than 20 cultivars of Hippophae rhamnoides, which is a valuable crop with a high carotene content in its fruits.

In China, from 1954 onwards plant introduction was scientifically organized and a major function of the newly established botanic gardens was ‘the exploitation of wild plant resources, introduction of indigenous and exotic, economic plants, breeding of new varieties so as to enrich the resources of cultivated plants’(Sheng 1980). The Wuhan Botanic Garden has been a centre for the introduction, cultivation, conservation and breeding of Kiwi Fruit (Actinidia) since 1980 and holds the world’s largest germplasm collection (57 species and 60 cultivars).

The Turpan Eremophyte Botanic Garden, a 7 ha area of sand which was planted with desert arboreal plants, undertook a project on the introduction and cultivation of fine-sand binder plants in association with the Biology Department of the Academia Sinica. Other examples of botanic gardens with special crop-based programmes are given by Sharrock (2006).

Countries are increasingly looking to their native flora as a source of potential ornamental crops, notably Australia (Plummer et al. 2000), Israel (Halevy 2000), South Africa, and E. Asia (Okhawa 2000) and in Latin America, Boyle (1991) has described the genetic resources of the native herbaceous ornamental crops as vital to commercial horticulture. A special Ornamental Plant Germplasm Center was created in the USA in conjunction with the USDA National Plant Germplasm System and Ohio State University (Tay 2003).

Botanic Gardens Conservation International (BGCI) facilitates access to information on species in cultivation in botanic gardens through its Plant Search database.

Acclimatization and acclimatization gardens: back in vogue?

The process of introduction of exotic germplasm was often carried out through the use of acclimatization gardens or stations where the aim was to allow the new plants to adapt to the new environmental conditions. The concept of acclimatization in the sense of gradual adjustment of plants or animals to new climatic or other ecological conditions other than those to which they are accustomed is highly debatable.Footnote 5 It is in effect essentially a selection process rather than any physiological adaptation of individual plants or animals although some plants can be hardened off through gradual exposure to colder temperatures (this is sometimes distinguished as ‘acclimatation’ as opposed to acclimatization) while others succumbed to the cold as even Linnaeus was able to show in his acclimatization trials in the eighteenth century (Koerner 1999). But it was widely practised and the 1860s witnessed a tremendous burst of enthusiasm for acclimatisation experiments for both plants and animals. As Weigl (2003) comments, acclimatization as such was an important aspect of colonialism in that the survival of settlers depended on the successful survival of the plants and animals they brought with them and Hardy (1860) went so far as to say that ‘The whole of colonization is a vast act of acclimatization’ (transl. by Weigl 2003). Acclimatization societies were established in most of the British colonies. On the other hand, the comment of Francis (1862) ‘So new to the world is the subject of acclimatization, as now understood, that it has little literature, and the advocates of it little experience’ could almost have been written today as although the subject matter is no longer new, our comprehension of it remains poor.

Acclimatization was a somewhat haphazard affair in the period of the first introductions from America and only in the following centuries were various acclimatization gardens created in Spain for the plants brought from overseas (see detailed discussion by Puerto Sarmiento 2002). Although Cadiz was the main reception centre for seeds and plants during the eighteenth century, arguably the most important acclimatization garden was that of La Orotava on the island of Tenerife, Canary Islands founded in 1788 and still surviving today as a botanic garden. The plants were then transferred to the now defunct botanic garden at the Puerto de Santa Maria before being sent to Madrid. Of course, many of the species successfully cultivated in La Orotava did not survive their subsequent shipment to the mainland or withstand the harsh climate of the Castilian meseta and most of them succumbed. Others could only be grown under protection in orangeries or similar structures which were developed in response to the custom that started towards the end of the fifteenth century of growing oranges, lemons and other tender trees in Europe.

At the Royal Gardens of Aranjuez, Philip II attempted the acclimatization of species from all around the world. Species which fared well included southern magnolia (Magnolia grandiflora), tulip poplar (Liriodendron tulipifera), sugar maple (Acer saccharum), boxelder maple (Acer negundo) and black locust (Robinia pseudoacacia). In Madrid the Royal Botanic Garden also played a prominent role in both the dissemination of material of the introduced species to other parts of Spain as well as undertaking acclimatization experiments. One of the most celebrated is the Rio de Janeiro Botanic Garden which was founded in 1808 for the introduction and acclimatization of economically beneficial plants brought from other tropical regions of the world.

Much of what is termed acclimatization is no more than successful introduction of exotic organisms. Some biologists are highly critical of the whole concept of acclimatization. Low (2002), for example, calls it ‘one of the most foolish and dangerous ideas ever to infect the thinking of nineteenth-century men’. To some extent, the notion of acclimatization is tainted with its association with the now discredited theories of Lysenko who himself, according to Weiner (1985) attempted ‘to identify I. V. Michurin, the horticulturist, as the source of his own inductionist ideas about heredity’ although the real roots of these ideas are still shrouded in mystery. On the other hand, the concept of acclimatization is regaining some its earlier interest because of the growing concern with the possibilities of the adaptation of plants to climate change.

Plant introductions and the risk of invasions

While the majority of plant introductions have had a positive result in terms of human welfare (Mack 2005), and indeed few countries could have survived and developed by relying only on their native germplasm, inadvertently some of the introduced species have proved to have characteristics that make them invasive in some regions. Invasive species have mostly been introduced for horticulture through nurseries, botanic gardens or individuals (Reichard and White 2001). It is estimated that 80% of current invasive alien plants in Europe were introduced as ornamental or agricultural plants: seriously invasive plants introduced deliberately as ornamentals include Japanese knotweed (Fallopia japonica), summer lilac (Buddleja davidii), common rhododendron (Rhododendron ponticum) and giant hogweed (Heracleum mantegazzianum).

Ironically, the very characteristics that make some species attractive for introduction (ease of propagation, fast‐growing, adaptable, high reproductive output, resistance to pests and diseases, tolerant of disturbance and a range of environmental conditions) are the same properties that increase the likelihood of the species becoming invasive (Heywood 1989; Dehnen-Schmutz et al. 2007a; World Bank 2009). Repeated local introductions through market outlets and development of traits that would increase the likelihood of escaped plants establishing themselves are considered equally important in the invasion process (Mack 2000; Kowarik 2003) and in an analysis of the British domestic market from 1885 to 1985, Dehnen-Schmutz et al. (2007a, b) showed that invading species were on average sold by more nurseries than non-invading species and that the probability that a species would escape from cultivation was significantly greater when more frequently available in the market and seeds sold at lower prices.

Botanic gardens, especially in the tropics, are often implicated as a source of plant invaders. One of the earliest examples recorded was that of false acacia (Robinia pseudacacia), native to the southern Appalachian and Ozark mountains of the United States, which was introduced to the Jardin Royale des Plantes Médicinales (later the Jardin des Plantes) Paris in 1635 as an ornamental tree by Vespasian Robin (1579–1662). It was subsequently widely cultivated for agricultural and commercial uses and has now become a serious invasive in several areas of the world, including Europe and parts of the USA. The black wattle (Acacia mearnsii), one of the world’s worst invaders (Lowe et al. 2000, 2004), native to Southeast Australia and Tasmania, was introduced into the Cape Town Botanical Gardens, South Africa in the 1830s and its seeds (along with those of other Australian Acacia species and Australian tea tree (Leptospermum laevigatum), were then supplied to the Grahamstown Gardens, thus contributing to the infestation of the Eastern Cape. A. mearnsii subsequently invaded shrublands, grasslands and savannas and now occupies some 2.5 million ha.

Because botanic gardens are one of the major sources of potentially invasive species, they have an obligation to take active steps to screen new introductions for potential invaders. The risks of introducing invasive plant species and their likelihood of escaping may be assessed using some form of risk analysis and assessment and various approaches exist (Heywood and Brunel 2009; Reichard 2000). Botanic gardens should consider adopting the International Standard on Phytosanitary Measures No. 11 on Pest Control (ISPM 2004) as adapted by the European and Mediterranean Plant Protection Organization (EPPO 1997) which is in the form of a decision scheme. Various national schemes have been published, for example in the UK (Baker et al. 2008), Australia (Biosecurity Australia 2001), Germany and Austria (Essl et al. 2009). The National Tropical Botanical Garden, Hawaii, USA, has adopted the Hawaii-Pacific Weed Risk Assessment (HWRA) to screen new plant imports as well as its existing collections for potential invasives). The HWRA is a research collaboration between the University of Hawai’i and the US Forest Service which developed and evaluated an adaptation of the Australian/New Zealand Weed Risk Assessment protocol for use in Hawaii and other high Pacific islands.Footnote 6 The Hawai’i Exotic Plant Evaluation Protocol provides an additional level of screeningFootnote 7 (see also Jefferson et al. 2004).

Tropical botanical gardens are considered to have played an important role in the distribution, naturalisation and spread of non-native plants worldwide and Dawson et al. (2008) used the Amani Botanical Garden (ABG), Tanzania, as a case study to highlight appropriate methods to assess the risks posed by existing and future collections in such gardens. The results of the study are summarized in Table 3.

Table 3 Invasion risks of the collections in the Amani Botanic Garden, Tanzania (from Dawson et al. 2008)
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Plant introduction and global change

With the growing world population and an estimated required doubling in food production needed by 2050, we are now facing demands for a major acceleration in the development of improved crops with higher productivity. There will be parallel demands for improved industrial and energy crops (El Bassam 1996). A substantial increase in research is needed, ranging from genetic and ecophysiological studies and screening for suitable germplasm, to understanding and characterising the growth and function of plant phenotypes as a whole (plant phenomics).

Accelerated climate change will have serious consequences for horticulture, agriculture and forestry with displacements of the major cultivation zones in some parts of the world. This will lead to a demand for the introduction of new and adaptable exotic species for agriculture and to meet increasing demands for biofuels and restoration and reforestation (World Bank 2009). In addition, crop cultivars will in many cases need to be reengineered so as to be suitable for the new range of environmental conditions in the displaced climatic zones, such as day-length, soil conditions, water quality and availability. Crop wild relatives will assume an even greater importance as sources of desirable characteristics to develop cultivars adapted to these new conditions.

We are presently over-dependent on a few plant species: global food security relies increasingly on a handful of crops with more than half of the daily global requirement of proteins and calories being met by just three crops—maize, wheat and rice; only 103 species of food plant provide 80% of our per capita supplies (Prescott-Allen and Prescott-Allen 1990); and only 150–200 crops are grown commercially on a significant global scale. On the other hand, ethnobotanical surveys indicate that, worldwide, more than 7–8,000 plant species are cultivated or harvested from the wild (Rehm and Espig, 1991). While we will continue to rely on the major staples for our basic nutrition, the need to broaden the basis of agricultural production and diversification of crops, especially those that are termed ‘underutilized’, with a view to making a significant contribution to improved health and nutrition, livelihoods, household food security and ecological sustainability is now receiving increasing attention (e.g. Batello et al. 2004; Frison et al. 2006; Heywood 2008; WRI 2005).

Underutilized crops are difficult to define and various terms have been applied to them such as ‘neglected’, orphan’, ‘minor’, ‘promising’, ‘niche’ and ‘traditional’ which are often used interchangeably. The Strategic Framework for Underutilized Plant Species Research and Development (Jaenicke and Höschle-Zeledon 2006) uses the following definition: ‘those species with under-exploited potential for contributing to food security, health (nutritional/medicinal), income generation, and environmental services’. Most of these species form part of local dietary complexes and are grown on a small scale in traditional agricultural systems alongside or to complement the staples that are cultivated. Many if not most of them are at the lower end of the domestication spectrum while others are wild-harvested (Heywood 1999a, b). They not only add variety to local diets but often supply much if not most of the daily requirements for vitamins, minerals and trace elements (Guarino 1997; Ogle et al. 2001). Recently two of the major initiatives involved in developing these resources, the Global Facilitation Unit for Underutilized Species and The International Centre for Underutilised Crops (ICUC), combined forces as Crops for the Future,Footnote 8 which is hosted in Malaysia by Bioversity International in a joint venture with the University of Nottingham, Malaysia Campus. A global search has begun for food crops with traits that are able to withstand changes to the climate. The project, co-ordinated by the Global Crop Diversity Trust, is searching national seed banks for ‘climate proof’ varieties, including maize and rice. The team will screen seeds for natural resistance to extreme events, such as floods, droughts or temperature swings. They hope the strains will help protect food production from the impacts of climate change.

Another important initiative was the launch in 2006 of the Global Horticulture Initiative (GHI) following 2 years of consultations involving ISHS, AVRDC, CIRAD, the Consultative Group on International Agricultural Research (CGIAR), the Global Forum for Agricultural Research (GFAR), some key national agencies for international development (USAID, GTZ, CIDA, CTA and others), and many other agencies, institutes and universities. ‘The motivating idea was that the value of horticulture enterprise for improving incomes and life quality in developing countries has been seriously under-recognized. It follows therefore that agencies conducting or supporting research for development should put greater emphasis on horticulture and a “Global Initiative” is needed to initiate, coordinate, and advocate for more horticulture research for development’(Anon 2006).

Globally botanic gardens are custodians of as many as 100,000 species of cultivated plants and countless cultivars, some of which have considerable potential for development and exploitation. Many gardens do not, however, have a collections policy and much of what is cultivated is the result of ‘serendipitous collectionism’, owing more to the transient interests of individual staff members than to any institutional policy decision. The collections are often of limited value scientifically or as conservation material because of their inadequate sampling, documentation and long-term sustainability (Laliberté 1997; Heywood 1999a, b, 2009b) although some of these collections are spectacular and attract great public interest.

If one considers that most of the underutilized species are local and seldom attract the attention of commercial companies or agricultural development agencies, there is clearly a gap that botanic gardens might be able to help fill. This will often involve working with local communities and integrating community-based action on indigenous crops and wild-collected or semi-domesticated species and traditional knowledge into climate change adaptation strategies. BGCI has encouraged gardens to play a more active role through its recent report Botanic gardens linking biodiversity with improvements to human well-being (Waylen 2006) and a number of botanic gardens are engaged in promoting the cultivation and use of local, underutilized plants for improved nutrition and health among their local communities (Waylen 2006; Sharrock 2008). So far, not many are involved in such developments, reflecting the tendency of botanic gardens not to form close links with commercial horticulture or participate in the activities of such bodies as the International Society for Horticultural Science (ISHS).

Climate change and the potential spread of invasive alien plants

A recent World Bank report (2009) notes that ‘Climate change is likely to aid the spread of invasive alien species, further threatening agricultural productivity and food security through spread of weeds, pests, and diseases of crops and livestock. The introduction of new and adaptable exotic species for agriculture and to meet increasing demands for biofuels, mariculture, aquaculture, and reforestation presents a particular challenge.

It is likely that there will be an increasing demand from the gardening public for species that will be more suited to growing in the new ecoclimatic conditions. The indirect effects of climate change, such as shortage of water, will have a serious impact on gardening and the kinds of plantings. An increase in demand for drought-resistant plants such as cacti and succulents is to be expected. The higher temperatures will increase the number and diversity of species that can be cultivated in some countries while in other countries these temperatures will cause stress and restrict the growth of many species. Flowering and fruiting times of some species will be affected and there will be a demand for new cultivars adapted to the new ecoclimatic conditions. The selection of trees cultivated will have important impacts on our landscapes. In some regions, species that can only be cultivated with difficulty today will prosper and some of them will escape from cultivation, becoming invasive.

As I have noted elsewhere (Heywood 2009a), perhaps the greatest dormant risk is the large number of plant species grown in gardens that currently survive outside their optimal climatic conditions in the reduced competition environment of cultivation. The great range of southern Mediterranean and South African grasses that are now becoming popular garden plants may offer the greatest threat yet to the native flora of Europe as these grasses are being chosen specifically for their toughness and ability to survive greater climatic extremes.

Another development that carries with it considerable potential risks is the expansion of the installation of green roofs and living walls. According to a recent report, ‘more than 14% of flat roofs in Germany have been greened and in Switzerland this number has reached 12%. In Asia, a city such as Tokyo requires today that all new buildings greater than 1,000 m2 must have 20% of their roof surface greened; the objective is to reduce temperatures in the city by 1°C. In North America, green roof surface area has increased by 30% in 2007, attaining a total of 370,000 m2 (Trépanier et al. 2009). Although these initiatives are very much to be welcomed as a contribution to the sustainable use of roof space and the reduction of the carbon footprint of buildings, care need to be exercised in the selection of species to be used for this purpose. So far, the green roofs and walls have incorporated only a small number of species, often drought tolerant stonecrop (Sedum spp.) with little invasive potential, but these new growing spaces are now attracting more creative horticultural use and this has led to a much wider range of species being introduced from other parts of the world. Moreover, these species are being selected for their ability to establish from seed on substrates such as crushed concrete and other industrial waste in the harsh environment of a green roof (Hitchmough 2008). Such pre-selection for tolerance and competitiveness could result in an alarming scenario whereby an elite set of introductions will spread from their roof and wall habitats along roads and pavements through cities and into suburban areas, generating a wave of weedy but decorative invasive.

Concern has been expressed at the possible risks of some of the species being introduced as biofuel crops becoming invasive. Buddenhagen et al. (2009) for example comment that ‘Despite reservations about their adverse environmental impacts, no attempt has been made to quantify actual, relative or potential invasiveness of terrestrial biofuel crops at an appropriate regional or international scale, and their planting continues to be largely unregulated’.

Botanic gardens and domestic gardens can be unintentional agents of assisted migration. In a recent study, Van der Veken et al. (2008) compared the native ranges of 357 native European plant species with their commercial ranges, based on data from the holdings of 246 plant nurseries throughout Europe and found that in 73% of native species, the commercial northern range limits exceeded natural northern range limits, with a mean difference of ~1000 km. They comment that ‘With migration rates of ~0.1–5 km per year required for geographic ranges to track climate change over the next century, we expect nurseries and gardens to provide a substantial head start on such migration for many native plants. While conservation biologists actively debate whether we should intentionally provide “assisted migration”, it is clear that we have already done so for a large number of species’.

Need for adoption of stricter guidelines and protocols

Since the coming into effect of the Convention on Biological Diversity, plant introduction has to operate under a new and developing regime of access and benefit sharing. Botanic gardens must ensure that the recently adopted Bonn Guidelines on Access to Genetic Resources and Fair and Equitable Sharing of the Benefit are properly implemented (CBD 2002). Gone are the days of free and unlimited access to plant resources across the world, sometimes referred to as colonial, ecological or green imperialism (Brockway 1979; Crosby 1986; Grove 1995; Drayton 2000), now replaced by national sovereignty and often quite severe access restrictions. Some botanic gardens have developed protocols or agreements for plant collecting which ensure the sharing with the host country of any benefits that might be derived from the use and exploitation of plant material collected. In the United Kingdom, several of the major Botanic Gardens, such as Royal Botanic Garden Edinburgh, National Botanic Gardens, Glasnevin and Royal Botanic Gardens Kew have already implemented guidelines compliant with the CBD to their own collections whereby they will only accept, exchange or transfer plants with organizations or individuals that they are confident will treat the material with due regard and undertake the same responsibility in growing it and in its further distribution. A requirement is that no plant material can be accepted without proof that it was collected in a bona fide manner with the appropriate agreements and Prior Informed Consent of the countries of origin (PlantNetwork 2009). Many European botanic gardens belong to the International Plant Exchange Network (IPEN), an exchange system for botanic gardens for non-commercial exchange of plant material, based on the CBD. Gardens joining the network must sign and abide by a Code of Conduct that sets out gardens’ responsibilities for acquisition, maintenance and supply of living plant material and associated benefit-sharing. To ensure proper compliance with the access and benefit sharing requirements under the CBD, such agreements should become the norm. There is also a voluntary International Code of Conduct for Plant Germplasm Collecting and Transfer developed by FAO in 1993Footnote 9 which aims to promote the rational collection and sustainable use of genetic resources, to prevent genetic erosion, and to protect the interests of both donors and collectors of germplasm.

Although botanic gardens have been exchanging plants within the confined circles of the global botanic garden estate, through the Index Seminum (Seed List) system or by despatch of living plants, they are not usually suited to the commercial dissemination of new introductions, a role that corresponds primarily to the horticultural trade, especially nurseries. The introduction of species, especially ornamentals, into cultivation is an important and largely untapped field for many botanic gardens today and deserves much further consideration (cf. Heywood 2003). There is however a need to work in much closer cooperation with the horticultural trade than has been customary in many instances. As Del Tredici (2000) points out, the relationship of botanic gardens to the plant introduction process differs from that of the horticultural trade, with the latter more focussed on the distribution of plants than on their ecology or taxonomy. ‘Given this complementary division of both labor and interest it makes sense for botanical gardens and nurseries to cooperate with one another on the introduction of new plants.’ Example of such cooperation can be found in Australia at the National Botanic Garden, Canberra where about 30 plants from the wild are cultivated each year and passed to the Australian Nurserymans Association for distribution to the general public. In addition, the Nursery Industry Association of Australia has very much concerned itself with environmental issues and with the commercial exploitation of native species: many rare or threatened Australian species are now established in nurseries and grown in gardens working in association with the Australian National and other botanic gardens.

Guidelines and codes of conduct for invasive species

As Dawson et al. (2008) point out, little appropriate guidance is normally available to botanic gardens regarding risk assessments of botanic garden collections. Because botanic gardens are one of the major sources of potentially invasive species, they have an obligation to take active steps to screen new introductions for potential invaders and a growing number of gardens are adopting policies to this end.

Several of the IUCN Guidelines (2002) are highly relevant to botanic gardens, for example:

  • ‘ex situ conservation should only be initiated when an understanding of the target taxon’s biology and ex situ management and storage needs are at a level where there is a reasonable probability that successful enhancement of species conservation can be achieved; or where the development of such protocols could be achieved within the time frame of the taxon’s required conservation management, ideally before the taxa becomes threatened in the wild. Ex situ institutions are strongly urged to develop ex situ protocols prior to any forthcoming ex situ management. Consideration must be given to institutional viability before embarking on a long term ex situ project’.

  • ‘all ex situ populations should be managed so as to reduce the risk of invasive escape from propagation, display and research facilities. Taxa should be assessed as to their invasive potential and appropriate controls taken to avoid escape and subsequent naturalisation’

The Council of Europe has prepared a Code of conduct on horticulture and invasive alien plants (Heywood and Brunel 2009) and at a national level, the United Kingdom has published a Code of Practice for Horticulture aimed at preventing the spread of alien invasive species (DEFRA 2005). Other Codes or guidelines aimed specifically at botanic gardens include the German-Austrian Code of Conduct for the cultivation and management of invasive alien plants in Botanic Gardens (Kiehn et al. 2007). In the USA, the St Louis Voluntary Codes of Conduct that arose out of a workshop “Linking Ecology and Horticulture to Prevent Plant Invasions” that was held at the Missouri Botanical Garden in St.Louis in December 2001, includes a Code for Botanical Gardens and Arboreta (Fay et al. 2001). A follow-up workshop was held in 2002 at Chicago Botanic Garden (Fay et al. 2002). Several US botanic gardens have endorsed the Voluntary Codes. However, as Dehnen-Schmutz and Touza (2008) point out, such codes or guidelines have no specific targets or time-frame and their effectiveness depends largely on how well they are promoted.

Summary: broadening the mission

Global change is causing a major reassessment of our priorities in many aspects of human activity including nutrition and food supply, health, development of energy crops, agriculture, horticulture, forestry, monitoring of, adaptation to and mitigation of climate change, and a wide range of conservation activities (including education). There will be a need for new plant introductions and breeding of appropriate germplasm. Botanic gardens have an unprecedented opportunity to play a part in many of these activities using their unrivalled skills and experience of growing, establishing and propagating plants. It is suggested that botanic gardens consider:

  1. 1.

    Broadening the plant introduction and exploration mission so that they can respond to some of the demands for new germplasm in response to climate change and not just for ornamental horticulture. Botanic gardens should consider working more closely with the agricultural and genetic resources communities in areas such as collection and conservation of:

    • crop wild relatives for which there will be an increasing demand in the face of global change;

    • economically and socially valuable wild species such as those which contribute significantly to nutrition and health; and

    • minor and underutilized crops, including oil and energy crops

    and working with local communities in the assessment, evaluation and improvement of local crops and semi-domesticates

  1. 2.

    Closer cooperation with agricultural genebanks. Botanic gardens and agricultural genebanks have different strengths and missions but they are complementary and there are obvious opportunities for synergies which will further both the mission of plant introduction and the global conservation effort.

  2. 3.

    Forging agreements between botanic gardens and the agricultural sector on precisely which species/species categories/genepools should be their conservation responsibilities so as to avoid duplication of effort

  3. 4.

    Improving the quality and sampling of accessions. Consideration should be given to defining rigorous standards in cooperation with the genetic resources sector for collecting, conserving and documenting activities, including:

    • sampling procedures,

    • seed and in vitro storage conditions,

    • viability testing procedures, accession sizes, and

    • adopting and adapting ecogeographical survey techniques and sampling protocols.

  4. 5.

    Undertaking proper evaluation and assessment of plant introductions before they are disseminated. Getting the plants into the country is not the most important part of the introduction programme but the first step.

  5. 6.

    Information on the accessions of introduced plants and their fate and its dissemination. The essence of any botanic garden is the plant collections that it grows and globally botanic garden accessions represent an extraordinary network of centres of plant diversity (albeit mainly cultivated) and constitute a major but much undervalued and certainly underutilized biodiversity resource. Despite the best efforts of BGCI and other bodies to assemble data on botanic garden holdings, it remains remarkably difficult to find out what is out there in the collections of the world’s botanic gardens, let alone any details of the accessions, how to grow and propagate them, which gardens hold duplicates, and so on.

  6. 7.

    Taking full cognizance of policies to protect against invasive species and due care taken to evaluate the risks that new introductions might represent. Consideration should be given to preparing a set of guidelines or even a code of conduct for plant introductions by botanic gardens in association with other agencies.