Citation Detail: XU Zaifu.1996. The Status and Strategy for Ex Situ Conservation of Plant Diversity in Chinese Botanic Gardens — Discussion of Principles and Methodologies of ex situ Conservation for Plant Diversity. in: Conserving China's Biodiversity (John MacKinnon, WANG Sung and etc.eds.). China Environmental Science Press. Beijing. 79-95p.

The Status and Strategy for Ex Situ Conservation of
Plant Diversity in Chinese Botanic Gardens
— Discussion of Principles and Methodologies of
ex situ Conservation for Plant Diversity　

XU Zaifu
(Xishuangbanna Tropical Botanic Garden,Chinese Academy of Sciences, 
Mengla 666303,Yunnan Province, China) 　

★[ABSTRACT]★[FOREWORD]  
★[THE STATUS OF CHINESE FLORA CULTIVATED IN CHINESE BGs]
★[ THE MAIN ISSUES IN EX SITU CONS-ERVATION OF PLANT DIVERSITY IN CHINA]
★[SOME STRATEGIES FOR EX SITU CONSERVATION OF RARE AND ENDA-NGERED SPECIES IN THE BGs OF CHINA] ★[ACKNOWLEDGMENTS]

ABSTRACT　
About 120 botanic gardens (arboreta) have been set up in China, and since 1989 they have shouldered the heavy tasks of ex situ conservation and research on rare and endangered plants of China. By 1993, about 18,000 species of Chinese flora have been cultivated in these botanic gardens, accounting for 65% of the total species of China. Three hundred thirty two species of rare and endangered plants, accounting for 85% of the total species (389) listed in the first batch of protected plants, have been preserved in 48 botanic gardens. Among 640 species of plants of the unpublished second batch, 154 species have been cultivated in 25 botanic gardens, accounting for 25% of the total. Moreover, a great number of living collections, arboreta and gardens for economic plants, flowering plants, and special families and genera have been established in these botanic gardens. These institutions have made a great contribution to the ex situ conservation of plant diversity in China.　

However, only a few botanic gardens have been set up in the regions with the highest plant diversity in China or in areas containing special ecological environments. In addition, the three distribution centers of Chinese endemic plants are poorly represented by existing botanical gardens. There are 15,000 to 18,000 species of plants in China that have been neglected in conservation plans. Thus, the efficiency for conserving endangered plants is still very poor. For instance, 66% of endangered species are only cultivated in one-to-four botanic gardens. Only one-to-ten plants from each of 63% of species are planted in these botanic gardens, and 10% of them are not growing well. Ninety percent of these are still young plants, although they are growing well.　

Research has shown that we must develop programs and establish some new botanic gardens as well as emphatically support the botanic gardens which have better foundations in order to achieve the goal of ex situ conservation on rare and endangered plants proposed in "The National Ten Years’ Programme for Environment" and "The Actions for Chinese Biodiversity Conservation." In addition, we must use the experience of selected units to promote work in the entire area so as to form a Natural Conservation Network. The establishment of authoritative institutions like "The Secretariat for Plant Ex situ Conservation in the Botanic Gardens of China" and "The Monitoring Centre for Plant Ex situ Conservation of China" should be considered so as to coordinate, monitor and guide ex situ conservation and research on plant diversity in the botanic gardens of China.

As the ex situ conservation of biodiversity is a kind of public welfare facility which is closely related to economic development and the ecological environment, direct economic profits can't be gained from the conservation and research. Great and continuous support from government, social and international institutions are urgently needed to raise money so as to establish the "China Foundation for Ex Situ Conservation of Endangered Plants." Owing to the increasingly heavy burden on ex situ conservation of plant diversity and its difference from the traditional work of plant introduction and acclimatization of the botanic gardens in China, new training in concepts, theories and methods for ex situ conservation is needed. In addition, international cooperation and communication are necessary so as to raise research standards and efficiency of conservation.

Key Words: Plant diversity, ex situ conservation in China, status and strategy, principles and methodologies

1. FOREWORD
Approximately 10% (30,000 species of higher plants) of the flora of the world is distributed throughout the 9,600,000 km² of special geographical situations, landforms and geological history in China. Of these, 2200 species are Bryophytes, accounting for 8.7% of the world total; 2600 species are Pteridophytes, accounting for 21.7%; 200 species are Gynmosperms, accounting for 26.7%; and 25,000 species are Angiosperms, accounting for 10%. Therefore, the number of higher plants is the first among Asian countries, and the third in the world (Chen Lingzhi, 1993, J. A. Makenili, 1990). Plants are primary producers in ecosystems, thus biological diversity of plants provides very important material, cultural and environmental basis, as well as important conditions for the existence and development for other living things. Without plants, there will be no vitality on the earth.　

The occurrence, development and extinction of plants is like that of other living things. Estimates have shown that during the past four hundred million years, one species has gone extinct every 27 years (N. Myers, 1988). In modern times, however, the sharp increase of population, the unreasonable use of natural resources, and the rapid change of environment are expected to cause one fourth of the biodiversity on the earth (among which 75,000 species are plants) to be in serious jeopardy of extinction during the next 20-30 years. That is to say, the speed of extinction is about 1000 times faster than its natural process. Research has indicated that 10% of the plant species in the temperate zones are in danger, while the corresponding proportion in the tropics and subtropics is projected to be higher than 10%. The proportion of plant species in danger in China is about 15-20%; which means there are 4000-5000 species of higher plants now in great danger (Chen Lingzhi, 1993). As we approach the 21st century, the percentage of plants in danger of extinction will exceed one fourth if no effective measures are taken to improve the ecological environment and to reduce damage to the environment.　

In the 1980s, an action of "Saving plants is saving the human being itself" was proposed to the world. The crisis of biodiversity which the world faced was brought to the attention of scientists, governments, and the publics globally. "The Convention on Biological Diversity," initiated at the Congress of Environment and Development held by the United Nations in Brazil in June 1992, marked a new turn in understanding the nature through which governments and the public could effectively promote new developments in biodiversity conservation.　

Plant diversity conservation is an important component of biodiversity conservation. It mainly is comprised of in situ conservation, ex situ conservation and sustainable use of plants. Plant ex situ conservation refers to the overall preservation of living plants, which is called "field gene bank" and "living collection." The preservation of seeds is called "seed bank," and preservation of tissues and cells is called "gene bank" or "in vitro culture." There are about 1500 botanic gardens (arboreta) in the world, they possess a certain quantity of land. The introduction and cultivation of various plants available for scientific research, as well as public exhibition, have become their main characters since their establishment. It is indicated in "the Botanic Gardens Conservation Strategy," formulated by IUCN Plant Conservation Secretariat, that the major roles of botanic gardens (BGs) are the preservation of plant genetic resources, and the promotion in realizing the sustainable use of plant species and their ecosystems (WWF & IUCN-BGCS, 1989). Therefore, these gardens have become the important basis for the ex situ conservation of plant diversity, and they are contributing to the issues of conservation, propagation and public education. Most of the wild plant species have been preserved in the 1500 BGs of the world. The international coordination of plant ex situ conservation is being directed by the BGs Conservation Secretariat under the leadership of IUCN. This secretariat has now recorded the information for 20,000 species of plants cultivated in BGs, accounting for 8% of the plant species in the world (J. A. Makenili, 1990).　

The earliest embryonic form of BGs in China might be the Medicinal Botanic Garden established by the legendary "Shennong" in 2800 B.C.. It is regarded as the earliest botanic garden in the world (WWF, 1982). After that, the emperors, high officials, noble lords, and religious temple yards have set up many gardens and parks with names such as "Shanglin Garden," "Summer Mountain Villa" and "Dragon Palace." Some of these have remained active up to the present time, and they play an important role in the conservation of plant diversity. However, according to the definition of a BG and the generally accepted characteristics of BGs throughout the world, these gardens can not be regarded as "BGs" (WWF & IUCN-BGCS, 1989). In China, BGs established under the direction of botanical principles and methods started from the beginning of this century (i.e., Hengchun Tropical Botanic Garden (1906), Xiongyue Arboretum (1915), Taibei Botanic Garden (1921), and Nanjing Sun Yat-sen Botanic Garden (1929)) The 1950s was the first major period for the development of BGs in China. During this time, most BGs were established by the Chinese Academy of Sciences. Beginning with the 1980s, many new BGs were established, the majority of which were arboreta of the Forestry Department and BGs of the Urban Construction Department (Xu Zaifu, 1983). At present, about 120 BGs (and arboreta) have been set up in China. They have similar characteristics and focus on the introduction, acclimatization, extension and cultivation of economic plants. The BGs under the leadership of the Chinese Academy of Sciences and the Provincial Science and Technology Committees focus on botanical research, and at the same time, on the collection and cultivation of Chinese wild plants. The arboreta of the Forestry Department focus on forestry research, mainly collecting and cultivating trees. The BGs of the Urban Construction Department focus on horticultural research, collecting extensively ornamental plants both from home and abroad. The BGs of the Educational Department focus on research, and the collection and cultivation of plants for the purpose of teaching.　

My research has determined that BGs in China cover an area of 240,000 ha and employ about 3000 scientific personnel. In these gardens, about 180,000 species of Chinese flora have been introduced and cultivated. About 800 living collections (gardens) for special groups of plants have been set up in these BGs, most of which are open to the public. About 15-20 million visitors visit these gardens every year (Li Shengchen, 1991). It is clear that BGs in China have played an important role in the ex situ conservation of plant diversity and scientific education, and have laid a foundation for research on rare and endangered plants. It is pointed out in "The National Ten-year Programme for the Conservation to Environment" and "the National eighth 5-year' Programme" that until 2000, all the national protected species will be preserved in ex situ condition or artificial propagation, and that some of them can be re-introduced in certain quantity and areas. No doubt, the BGs in China will be the main force in realizing the tasks of these programs.　

2. THE STATUS OF CHINESE FLORA CULTIVATED IN CHINESE BGs
2.1 The number of species of Chinese flora cultivated in BGs　
I have collected the lists of plants cultivated in 34 BGs in China. These plants comprise the flora of China as well as some species which did not originate in China. In the lists of some BGs, many horticultural varieties are also included, and there are many overlapping species. Therefore, it is very difficult to get an accurate number of Chinese plant species cultivated in the BGs. The method of sampling of the BGs, therefore, must rely upon estimates.　

The lists of 15 BGs were sampled and the following information obtained: among the cultivated plants, about 80% are species and varieties, of the cultivated species (including varieties), 65% are Chinese flora. Moreover, statistics have been made on an index of overlap among the 486 species of rare and endangered plants of China cultivated in 45 BGs. The parameter is 4.9. So, the Chinese flora which are cultivated in the BGs of China may be as:　

　　　CF = 170000×0.8×0.65/4.9 = 18000 (spp.)

In the cultivated lists of plants provided by the BGs, only Pteridophytes, Gymnosperms and Angiosperms are included, while Bryophytes are excluded. These three types of plants comprise 27800 species in China. So, the cultivated plants in the BGs of China account for about 15% of the total flora of China. According to my investigation, some native plants in many BGs are excluded from their lists of cultivated plants. Therefore, the calculated number can not be higher than the actual number.　

2.2 The national protected species cultivated in the BGs　

The conservation of rare and endangered plants received increasing attention throughout the world at the beginning of 1970s. In 1974, the "Threatened Plants Committee" was set up by the "Species Survival Commission" of IUCN, and a book titled “IUCN Plant Red Data Book" was published, which has promoted the work for the conservation of rare and endangered plants in many countries. In 1980, an effort to produce and compile a "China Plants Red Data Book" was started by experts organized by the Institute of Botany, Academia Sinica under the leadership of the former Environmental Protection Leading Office of the central government. The first volume of this book was formally published by Science Press in 1991. Moreover, efforts to compile the second volume of this book was started by the Institute of Botany, Academia Sinica and supported by the National Bureau of Environment in 1988. Therefore, in the early 1980s, research on conservation of rare and endangered plants and subsequent conservation action had been started in China. And from then on, a few BGs belonging to the Chinese Academy of Sciences (e.g. Xishuangbanna Tropical BG, Beijing BG and Nanjing Sun Yat-Son BG) have started research on ex situ conservation of endangered plants. Recently, statistical figures on national protected plants cultivated in BGs have been collected from "China Data-base on Rare and Endangered Plants" in the Institute of Botany, Academia Sinica, and from 27 BGs, as well as some other data. Results of this survey are presented in Table 1.　

Table. 1, Rare and endangered species conservation ex situ in Chinese BGs

Table 1 shows that 332 species of the first batch of 389 species of national protected plants have been planted in 45 BGs, accounting for 85.3% of the total. My estimate of the number of such species in all 120 BGs in China is 350, accounting for about 90% of the total. For the 640 species of the second batch of nationally protected plants, though they haven't been promulgated formally by the country, 154 species are found in 25 BGs, accounting for 24.1% of the total. I estimated that 200 of these may be found in all 120 BGs, accounting for about 30% of the total. Among the first and second batches of endangered plants cultivated in the BGs, Gymnosperms are represented by a high proportion, while Angiosperms take second place. Pteridophytes are represented by the lowest proportion. This is because species identification for Pteriphytes is more difficult than for the others, and many protected species of Pteridophyte need special habitat (shade and humidity) and conditions for cultivation and the propagation of spores. These problems are difficult to overcome for many BGs.　

The BGs investigated which have preserved over 100 species of rare and endangered species as ex situ conservation are: Guilin BG (180 species), South China BG (152), Xishuangbanna Tropical BG (119), Shanghai BG (116), Nanjing BG (106), Beijing BG (100), Hangzhou BG (100), Lushan BG (100), Shenzhenxianhu BG (100) and Kunming BG (100).

2.3 Special groups of plants cultivated in the BGs　

Traditionally, BGs in China mainly focused on research on introduction and acclimatization of plant resources. They have introduced and cultivated economic plants both from home and abroad, and have made great contributions to the economic development of many regions through experiments and research. At present, many special living collections have been established for economic plants, arboreta, flowering plants and other special taxa through long-term accumulation. Among the BGs investigated, the living collections and gardens with distinctive features are as in Table 2.　

In the ex situ conservation of plants, the collection and cultivation of special groups of plants have come to be considered of great importance throughout the world. Some of these special collections have become national germplasm banks for plant resources, some of them have become research bases for special groups of plants, and many of them have formed strong distinctive features of these BGs. Associations for special groups of plants such as for Orchids, Rhododendrom, Camellia, Cycads and Palms, etc. have also been formed throughout the world. Some taxonomic groups from China represent a very important position in the world. Examples of these are: orchids (world total: 2000 species; China: 1019 species); camellias (220; 190); Actinidia (54; 52); Acer (200; 150); rhododendroms (500; 300); and primulas (500; 300). The investigation, collection and cultivation of these species should be strengthened, so that these special groups of plants can become the germplasm resource pool of China and even the world.

　Table 2.               Characteristic living collection of  special groups of plants in Chinese BGs

3. THE MAIN ISSUES IN EX SITU CONSERVATION OF PLANT DIVERSITY IN CHINA　

3.1 The serious imbalance of distribution of plant diversity and BGs in China　

Since different plants have distinctive biological characteristics and ecological adaptability, they correspondingly have distinctive geographic distributions. In order that plants can grow and regenerate normally in their ex situ habitats, so as to reduce artificial acclimatization and to save resources, experts both from home and abroad have adopted the viewpoint that BGs should mainly preserve the local floral element (WWF & IUCN-BGCS, 1989; J. B. Simmons, 1976, Xu Zaifu, 1990). Mr. He Shangan pointed out in 1991 that in China there are only a few BGs in the Himalaya forest subregions which are the most diverse in plant resources. The situation is very similar to the distribution of BGs in the world (WWF & IUCN-BGCS, 1989; WWF, 1984; He Shangan, 1991). Table 3 indicate the distribution of 104 BGs in China.

From Table 3, we can see that the issue of distribution of BGs in China not only concerns the Himalaya forest subregion, but also some regions with special habitats in China (i.e. the Qinghai-Xizang Plateau and the large area of dry hot valleys in south-west China) where there are only a few BGs. The hot dry valleys mentioned are those influenced by the "foehn effect" (the plants there have characteristics of both cold and hot resistance). In addition, the three primary distribution centers for endemic groups of plants in China (1) Eastern Sichuan -- Western Hubei; 2) Southeast Yunnan -- Southwest Guangxi and 3) Northwest Yunnan -- Southwest Sichuan) also contain only a few BGs.

Table 3.  Regionalization of Chinese flora and distribution of Chinese BGs
(Xu Zaifu, 1990; He Shangan, 1991)

Regionalization of Chinese flora	No. of BGs’ distribution
I. Halarcic kingdom	89
A. Eurasia forest subkingdom	1
B. Asiatic desert subkingdom	7
C. Eurasia steppe subkingdom	3
D. Qinghai-xizang Plateau sub.	1
E. Sino-Japan forest sub.	72
F. Sino-Himalaya forest sub.	5
II. Paleotropic kingdom	15
G.Malaysian subkingdom	15

In contrast, the majority of established BGs in China are centralized together and do not occur in the places of the richest plant diversity, special habitats or the centers of endemism of plants in China. In order that the precious, rare and endangered plants could be well-protected in ex situ habitats, a program for setting up some new BGs in the above mentioned places should be made. The establishment of new BGs should be meticulous in design and should absorb the experiences of the established BGs. Locations near nature reserves or near large-areas of natural vegetation should be chosen for the purpose of integrating conservation and research (WWF & IUCN-BGCS, 1989).

3.2 Conservation of Endemic Plants in China Has not been given Suitable Attention　

When the spatial range of a species’ distribution is limited to a restricted area, it is called endemism. The endemic plants of China refer to those plants only or mainly distributed in China. These species not only have important potential for the development of the economy, they are also easily threatened by human interference and environmental change because of their narrow distribution or small population size. Moreover, endemic species are important for us to understand the composition, character, occurrence, and density of floras in certain regions. The conservation of endemic plants has been greatly emphasized throughout the world. It has been pointed out that a community comprised many species of extensive distribution contributes less to the conservation of biodiversity than a community comprised of many endemic species. Furthermore, when fixing an area especially rich in biodiversity, the number of endemic species and the richness of species are two of the important standards (J. A. Makenili, 1990).　

China is not only one of the countries with the most abundant plant diversity in the world, but also has many endemic taxonomic groups. There are 7 endemic families among the seed plants of China (i.e. Cingkoaceae, Eucommiaceae, Nyssaceae, Kindoniaceae, Acanthochlamydaceae, Bretschneideraceae and Sargentodoxaceae). Among the higher plants, there are 256 endemic genera (Table 4), accounting for 6.6% of the total genera in China. In particular, endemic genera of Gymnospermae account for 25% of the world total. Endemic species in China amount to 15,000-18,000 species and account for 50-60% of the total species of China (Chen Lingzhi, 1993).

Table 4.  Endemic genera of Chinese higher plants

Types	No.of Chinese genera	No.of endemics	%
Bryophytes	494	8	1.6
Pteridaphytes	224	5	2.2
Gymnospermae	32	8	25.0
Amgiospermae	3116	235	7.5
Total	3866	256	6.6

The conservation of Chinese endemic species has strong distinctive features for our country and can avoid the repetition of species conservation in other countries. It is an important part in the species conservation of the world’s plants. However, the proportion of Chinese endemic species is relatively low in the lists of the first and second batches of national protected plants and in the lists of cultivated plants in the BGs of China. Therefore, when working out a plan for the conservation of plant diversity in China, the ex situ conservation of regional endemic species should be supported and encouraged. In addition, many BGs in China have neglected the species which have high priority for protected in the world, such as those species needed in the recovery and regeneration of ecosystems, as well as keystone species, isolation species, and wild types of cultivated plants and their relatives.　

3.3 Issues Concerning the Effectiveness of Ex situ Conservation of Rare and Endangered Plants in BGs　

The author holds that the effectiveness for ex situ conservation of rare and endangered plants in BGs involves:　

1) whether these plants can grow and regenerate normally and maintain their original genetic constitution in BGs;　

2) whether these species are repeatedly cultivated and preserved;　

3) whether they have a large enough population so as to reduce the loss of genetic diversity; and　

4) whether BGs have set up scientific recording systems.　

Below I discuss these issues in relationship to the current situation of BGs in China.　

3.1.1. The growth and adaptation of plants in ex situ habitats　

Whether plants can grow and regenerate normally in their new habitats, in other words "from seeds to seeds" is one of the standards used to judge whether ex situ conservation is successful. As the work of ex situ conservation for rare and endangered plants in the BGs of China started in the early 1980s, most of the plants can not come up to the standards of "from seeds to seeds." I have examined information on the first batch of nationally protected plants which are cultivated in BGs from "China Data-base on Rare and Endangered Plants," Institute of Botany, Academia Sinica. According to the statistics, 85% of these plants are growing well, 10% are not, and the other 5% cannot be determined. This result has shown that ex situ conservation of rare and endangered plants in the BGs of China is successful on the whole.　

However, there are critical issues facing the growth of these plants beyond the 10% of species that have been determined to be faring poorly. Of the 85% of species classified as growing well, most are seedlings, thus it is not easy to determine if these species meet the standards of "from seeds to seeds". Their growth is closely related to soil, climate and biological factors. Even if these plants are introduced to BGs in their climatic regions, it is still possible that they may meet some serious problems which will influence their growth, or lose genetic variation because of acclimatization (Xu Zaifu et al., 1985). Therefore, it is better to choose the floral elements of the regions where the BGs are located for ex situ conservation of rare and endangered plants, to create micro-habitats or niches similar to their natural habitats as far as possible according to their biological-ecological characteristics, and to make continuous adjustments according to their growth conditions. Recently, some propaganda organizations reported rashly the success in some ex situ conservation of rare and endangered plants, which is difficult for experts to believe. For instance, one report says in one-hectare of land in a BG, over 100 species of rare and endangered plants are planted. Some of these plants were introduced from the low elevations to about 50 meters above sea level, some from mountain areas 2000 metres above sea level, and some from high mountains and lime-stone mountains. If these plants have such extensive ecological adaptation, and can grow well in their ex situ conservation land, maybe they are not rare and endangered plants. Therefore, it is necessary to lay down a synthetic evaluation standard of success for ex situ conservation according to the objectives of species' conservation.

3.3.2. Overlap of cultivation of ex situ conservation plants in Chinese BGs　

There is no requirement for the rare and endangered species to be cultivated only in one BG in China. On the contrary, it is required to have overlap in the cultivation of a species among BGs for the purpose of safety. If one species is preserved in relatively isolated BGs, they may form a metapopulation and thus increase the probability of extinction or of causing inbreeding (just as if the populations were growing in different fragmented ecosystems; D. Simberloff, 1988. N. W. Morre, 1962). But, this situation can also reduce the mutual infection of insect pests and plant diseases caused by big populations. Furthermore, the individual migration between different populations of BGs may have certain significance for maintaining the viability of populations and their respective genetic diversities.

At present, there are no data to determine how many BGs should be represented for preserving one species. Of course, it is safer to preserve species in more BGs, but this question needs more investment. According to the situation of the degree of threat facing a plant and the BGs in China, we must determine whether it is most desirable to preserve a rare and endangered species in five (>=5) BGs. Naturally, certain different natural conditions of the five BGs also should be considered. If this decision is regarded as a standard, we can evaluate the present situation of preserving rare and endangered plants in the BGs of China (Table 5). From Table 5 we can see that among the first batch of protected plants in China, 51.5% of species are preserved in less than five BGs. The corresponding figure comes up to 95.5% among the second batch. In order to raise our efficiency in the conservation of rare and endangered plants, communication between BGs on population status of these plant species only planted in a few BGs should be encouraged and supported, and the future introduction of natural population should also be strengthened.

Table 5.  Overlap in cultivation of rare and endangered species in Chinese BGs

　3.3.3. The size of effective population for ex situ conservation

The conservation of species requires a big population for maintaining its genetic diversity. Thus the saying "the more the better" applies to conservation genetics of endangered species. It is difficult to maintain a big population in in situ conservation, to say nothing of ex situ conservation in BGs. Therefore, scientists are now studying "the minimum population - MP" or "minimum viable population - MVP" for species conservation. There are two kinds of generalized concepts for MVP. One is a genetic concept that consists mainly of the influence to the population of genetic loss and the decline of adaptability caused by inbreeding and genetic drift. These result in the minimum isolated population size needed for maintaining genetic variation in a certain time. The second concept concerns population statistics. This means the minimum isolated population size which can survive a certain time at a certain probability (W. J. Ewens et al. 1987; Li Yiming & Li Dianmo, 1994). Original research has shown that the size of MVP over short periods of time (say 50 years) should not be lower than 50. Correspondingly, over longer periods (100 years), MVP should not fall below 500 (I. A. Franklin, 1980). Some populations may fall to 30-50 or even lower in some disturbed ecosystems, and as these have been known to survive in some circumstances, a concrete analysis of existing conditions should be made in each case (M. Soule, 1986). It is worth mentioning that J. N. Eloff and L. W. Powrie made a morphological comparison on 10,000 plants propagated from three plants of Aloe spectabilis which had been in cultivation for 90 years, and found that these plants can no longer interbreed with the original plants from only 300 km away -- even though there is no obvious difference in their external morphology. So they suggested that it is not necessary to have a large population for certain plants in ex situ conservation (J. N. Eloff & L. W. Powrie).　

Although research on MP and MVP has become a hotpoint in conservation biology and has made great headway, there however is not a well-considered methodology for plants nor a criterion which can be extensively accepted. In addition, because of differences of population characteristics, genetic characteristics, ecological environments and degrees of threat for different species, the MVP required for any species may also be different (Li Yiming & Li dianmo, 1994). I proposed a formula on population size of protected plants in BGs in 1990 based on research from Charles Darwin (C. Darwin, 1916), Karl Esser (K. Esser, 1976) and R. W. Allard, as well as the requirement of 50-100 years for plant ex situ conservation (Xu Zaifu, 1990) as follows:　

Pn = Lf. Ee. Am　

In the formula, Pn refers to MP which should be protected; Lf refers to the number of plants required to be protected according to the life form of the species (i.e., 10-20 plants for arbor, 40-50 plants for shrub, 100-200 plants for herb; Ee refers to the number of ecological or genetic types distinguished; Am refers to the propagation system of the species. It was initially determined that a monoecious plant is 1.2, including self-pollination or cross pollination, a dioecious plant is 1.0, and the type of non-fusion reproduction is 0.80. This scheme is rough, but easy to execute, so it has been applied by some scholars on Chinese plants. This method is used here to make a preliminary study on the population size of rare and endangered plants cultivated in the BGs of China (Table 6).

Table 6. Size of population of protected rare and endangered species in Chinese BGs

As the life forms for rare and endangered plants and their propagation systems are different, and they have different ecological or genetic types, it is difficult to evaluate them with only one standard. Meanwhile, as discussed above, one species of rare and endangered plant should be preserved in at least 5 BGs for the purpose of safety. Here, suppose the requirement of MVP for ex situ conservation of each species is 10-20, which is the lowest standard to preserve its genetic diversity. This results in the statistical data presented in Table 6. Among the first batch of protected plants cultivated, only 25-38% have come up to the lowest standards, and some of these species have not been cultivated in more than five BGs. Among the second batch of protected plants cultivated, only 22-33% come up to the lowest standards. In addition, because ex situ conservation on rare and endangered plants in Chinese BGs was started only recently, many cultivated plants are still very young. Thus, there is an expected high death rate in their life period of "from seeds to seeds." Therefore, in order to maintain the effective population of the conserved species, BGs should be encouraged and supported to increase the population size of rare and endangered plants and acquire new seed origins. Under these circumstances, the BGs with small areas should prefer to preserve small number of species, so as to guarantee enough MVP for these species, rather than preserve a great quantity of species below that of this standard. Of course, the establishment of exhibition collections for biodiversity education is a different matter.

3.3.4. The establishment of scientific recording systems and monitoring centers　

BGs mainly adopt whole living plants for ex situ conservation and carry out long-term maintenance of the species through generation propagation. While 50-100 years are short to the goal of conservation, this time frame is very long to BGs. During this period, arboreous plants may propagate three or five generations, shrubs or herbaceous plants may propagate over ten generations.　

As it is described above, when plants are moved from their original habitats and ecosystems, even if they are planted in the same climatic region, they may still face problems concerning ecological adaptation -- such as soil, ecological, pests and diseases, pollination medium and relationships between species. All of these factors may affect their growth, propagation, genetic variation and gene flow, etc. These cases should be observed, studied, analyzed and recorded so as to adjust and control their growth conditions.　

With the progress of ex situ conservation on rare and endangered plants in BGs, the number of species are increasing and populations are also getting larger. The origins of one species are becoming diversified and have different ecological and genetic types. All the while, F1, F7, F3....etc. generations are increasing continuously. If scientific recording systems by computers are not established, the number of rare and endangered plants cultivated in BGs will become an unruly mess. Moreover, ex situ conservation and in situ conservation of rare and endangered plants in BGs supplement each other; their ultimate aim is to put the artificial propagates back into their original ecosystems, an action which is called "reintroduction." Reintroduction is a complicated scientific issue in conservation biology research. It is more difficult than introduction. If there are no detailed scientific data on the biological and ecological characters for a plant’s ex situ conservation, it's impossible to work out a scientific program on reintroduction.

Some famous BGs in the world have established complete sets of recording systems for ex situ conservation (WWF & IUCN-BGGS, 1989; Belizabeth et al., 1989). Arnold Arboretum of the United Sates published a book called "The Collection and Conservation of Germplasm Resources of Living Plants" in 1989 . In China, Nanjing BG has made a systematic study on recording systems and has published a book "Computerized Managing Systems on Recording Systems of plants in BGs" in 1990 (Gu Yin & He Shang-an, 1990). Up to now only a few BGs have set up recording systems in China, however inconsistent they may be. Maybe some BGs, like Beijing BG, Nanjing BG, Huhehot Arboretum, Kunming BG, Xishuangbanna BG, Fuzhou Arboretum and Minqin BG have set up or are about to set up computerized management systems.

One BG can only play a very limited role in the conservation of rare and endangered plants. Therefore, cooperation and communication between countries and regions have been greatly emphasized in the world so as to form a network at different levels. The BGCS is an organization established by IUCN in 1987 to coordinate the conservation work of BGs in the world. Later, IUCN, UNEP and WWF have cooperatively set up the "World Conservation Monitoring Centre” (WCMC). This center has stored the information on about 20,000 species of endangered plants world-wide (V.H. Heywood, 1991). China is a country with the richest biodiversity in the world and its flora in serious endangerment may be as great as 15-20%. About 120 BGs are carrying out the work of ex situ conservation of rare and endangered plants. In order that BGs can play an effective role in the ex situ conservation of nationally protected plants, an authoritative "China Botanic Gardens Conservation Secretariat" should be set up so as to coordinate the conservation work in Chinese BGs. And "A Monitoring Center for the Conservation of Chinese Rare and Endangered Plants" should be set up in the BGs with ample capacity to do so (i.e. Beijing BG). 　　

4. SOME STRATEGIES FOR EX SITU CONSERVATION OF RARE AND ENDANGERED SPECIES IN THE BGs OF CHINA　

4.1. A network of conservation based on BGs　

As described above, the BGs in China mainly focus their work on investigation, collection and cultivation of plant diversity, so they have good conditions either in land, equipment or scientific force etc. At present, about 18,000 higher plants (except Bryophytes) have been planted in the 120 BGs of China, accounting for about 65% of the floral elements in China. In recent years, many BGs have gradually diverted their research on the conservation of rare and endangered plants from traditional plant introduction and acclimatization, and have set up relevant ex situ conservation areas. For instance, Xishuangbanna Tropical BG has set up an "Ex situ Conservation Area for Rare and Endangered Plants of Southern Yunnan". The area contains 80ha and preserves both 1300 species of local plants, and rare and endangered plants. Among 389 species of the first batch of protected plants, 85-90% have been preserved in the ex situ conservation areas of Chinese BGs, while 25-30% of 640 species of the second batch have been planted, though not formally promulgated by the country.　

In order to achieve the goal of ex situ conservation on rare and endangered plants listed in the “National Ten Years Programme for Environment” and in “The Actions for Chinese Biodiversity,” BGs should be defined as a center of activity. IUCN has entrusted BGs with important tasks, knowing the important roles they have played in the conservation of nature and in other activities from “WWF-INCY Plant Movement” and “Plant Conservation” (WWF & IUCN-BGCS, 1989). As mentioned above, some new BGs should be set up in the regions with the most characteristics of high plant diversity in China (high species number, special habitats, and distribution centre for endemic species, etc.). An authoritative organization for coordinating ex situ conservation of BGs and a monitoring center for ex situ conservation of rare and endangered plants should also be set up so that human and material resources can be used effectively and exert the greatest influence on the conservation of plant diversity. But the overlapping establishment of so-called “Introduction and Propagation Centres” in the regions where already established good botanic gardens exist, should be avoided -- we would get half the results with twice the effort.　

4.2. Carrying out an ex situ conservation program -- main points　

It is estimated that there are 4,000-5,000 endangered species in China, and that this number will increase greatly. The ex situ conservation of rare and endangered plants is different from the traditional plant introduction and acclimatization. It requires BGs to emphasize their work on regional wild plants, to stress the conservation of genetic diversity (incorporating population as well as “Mutiple Genepool Sampling” (R.W.Allard, 1970; F. Thomas, 1976; J. G. Hawakes, 1976), and to establish a more complete scientific recording system. Furthermore, reintroduction for some species is also required in the conservation of species. Therefore, the programs of ex situ conservation for rare and endangered plants should incorporate the conditions of every BG, the distribution and ecological characters of rare and endangered species, and the requirement of protection so as to preserve the plants in their most appropriate BGs. And emphasis should be put on those species which have not been cultivated in BGs and those only cultivated in one or two BGs. Further, emphasis should be given to those species represented by only a few plants when preserving rare and endangered species. Programs are necessary for ex situ conservation of endemic species of China, as well as those species which are monotypic, wild types and relatives of important cultivated plants, important wild economic plants and keystone species in some ecosystems.　

Just as mentioned above, all BGs in China have historically shouldered huge tasks in the conservation of plant diversity. However, as ex situ conservation should be closely related with research work, and plant conservation is different from plant introduction and acclimatization, the investment on it is heavy and more investment is needed to maintain the work. Key points should be stressed when working out programs for ex situ conservation of rare and endangered plants. The BGs with good capacity should be supported so as to get twice the result with half the effort. The BGs being mainly supported should have the following conditions:　

1) Have permanent and stable financial support;　

2) Have a large area of land, less pollution and less artificial destruction, as well as contain diverse habitats;　

3) Have a strong scientific force, including capacity for field surveys, plant identification, ecology, genetics, horticulture and cultivation;　

4) Have good research equipment, including a herbarium and appropriate laboratories;　

5) Have the capacity to engage in scientific education on biodiversity conservation to the public.　

Those BGs with poor conditions can only assume some tasks of collection, cultivation, preservation and recording of some species. While for the BGs in cities, exhibition areas for rare and endangered plants can be established for carrying on scientific education to the public.

4.3 Finance and strengthening the intensity of maintenance　

The ex situ conservation of rare and endangered plants, including research on basic and applied techniques for conservation practices, requires significant funding. For example, Viera Clavija BG in Grand Canary Islands off Spain spends $300,000/year as preserving expenses, which is 30% of their budget (WWF & IUCN-BGCS, 1989). This financial commitment represents a form of social public welfare, because the results will benefit not only the present populace, but its descendants as well. The institutions who are engaged in research and conservation of rare and endangered plants usually can not achieve economic profits from their work. Even if the research is on sustainable use of plant resources, it is still difficult to get economic profits from its results without heavy investment. Although the BGs in China get different funds owing to their different affiliated organizations, they still have many difficulties with funding. Therefore, if there is no strong financial support, it will be very difficult for the BGs to undertake their research and practical work on ex situ conservation of nationally protected species. Moreover, the government should give proper preferential policy to the BGs for their small amount of income they get from activities of scientific education and some necessary tourism services for maintaining the diversity of plants cultivated in their gardens.　

With regard to research and the conservation action of rare and endangered plants, in addition to support from government, various channels should be opened up so as to raise funds and strengthen the intensity of maintenance. It is required to seek the donation and loan from international financial organizations (like the World Bank and the Asian Bank), international non-government organizations, developed closely cooperate with them. Moreover, donations from those enterprises who focus their development on plant resources and from individuals who show solicitude for the conservation of biodiversity in China is needed for establishing the "China Foundation for the Conservation of Rare and Endangered Plants."

4.4. Strengthening the training of scientific personnel and academic exchanges　

Plant diversity conservation is an important part of the newly developed conservation biology. Conservation biology is the scientific study of biodiversity in three levels -- genetics, species and ecosystems -- and the influences on these by environmental changes and human activities in order to carry out effective management and conservation of it so as to make sustainable use of the regenerated resources for human being (Xu Zaifu, 1991). Therefore, the ex situ conservation of plant diversity is a link between natural sciences and social sciences. Most of the BGs in China have started research on ex situ conservation of rare and endangered plants since the early 1980s, and they have accumulated a wealth of scientific data and gained significant scientific results. But, many of them have not changed from their traditional ideas of plant introduction and acclimatization. They have only a small understanding of the related new concepts, new theories and new methods which have been developed in recent years. Besides, many BGs in China are facing significant personnel problems -- who will be the next generation of scientific researchers, administrators, and skilled workers? In order that the BGs in China can shoulder the important task of ex situ conservation of plant diversity, necessary measures should be taken to strengthen the training of scientific personnel.　

Engaging in different subjects being organized to fulfill special topics on ex situ conservation of plant diversity, carrying out overlapping, infiltration of subjects and learning on the job are important methods for training scientific personnel. Organizing academic workshops, holding related international scientific conferences and encouraging scientific personnel to attend scientific conferences abroad are important methods to train and empower subject leaders. The BGs with better foundations should be supported to enroll graduate students and conduct periodical or short-period professional training courses. Some famous experts concerned should be invited to give lectures in China and to cooperate with each other. Some excellent students or scholars should be encouraged to engage in short-period advanced studies or to study for academic degrees in order to raise the standards of ex situ conservation and research on plant diversity in China. 　

ACKNOWLEDGMENTS　

The author would like to take this opportunity to thank Professors Wang Sung and Dr. John MacKinnon, Co-Chairmen of the Biodiversity Working Group, China Council for International Cooperation on Environment and Development for their encouragement to this research, Professor Xu Kexue of the Institute of Botany, Academia Sinica for providing relative information, and those BGs who provided precious data for this research. Thanks are also expressed to Ms. Zhou Shuanyun and Nie Wanzhi for counting and typing data, and to Ms. Li Liming for translating this paper into English. Professor Dr. Andrew T. Smith, of the Biodiversity Working Group, kindly edited the entire manuscript.

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