Abstract. China occupies a vast territory with a complex climate, varied geomorphic types, a large river network, many lakes and a long coastline, and great vegetational diversity. The forests of China can be divided into boreal coniferous forests, temperate, subtropical and tropical coniferous forests. deciduous broadleaved forests, evergreen broadleaved forests, tropical seasonal rain forests, rain forests and mangrove forests. In addition, there are mixed coniferous and deciduous broadleaved forests and mixed evergreen and deciduous broadleaved forests. It should also be mentioned that in China, there are specific coniferous forests consisting of plants more widely distributed as fossils and which are relicts of the late Tertiary or even older geological periods. These forests contain Cathaya argyrophylla, Pseudolarix kaempferi, Metasequoia glyptostroboldes, Glyptostrobus pensilis, Taimania cryptomerioides and T. flousiana. Boreal coniferous forests can be classified into larch, spruce, fir, pine, and Sabina forests. Pinus forests from temperate to tropical regions exhibit a geographical species replacement phenomenon. Deciduous broadleaved forests are mainly dominated by oak, birch, poplar, linden, maple, elm, etc. Evergreen broadleaved forests include various species of Castanopsis, Cyclobalanopsis, Lithocarpus, Maclulus and Schima. Tropical forests are rich in species with limited areas of distribution.

Key words. forests, diversity, China, conservation, nature reserves

China is located in the southeastern part of the vast Eurasian continent. The southeastern part of China borders the Pacific Ocean while the northwestern part extends to the center of the Eurasian continent. The total area of China is 9.6 million km. Within this vast area there is a transition from cold temperate to temperate. warm temperate, subtropical and tropical climatic zones from north to south. The vegetation, flora and fauna obviously reflect the horizontal distribution of these zones. Coniferous forests, mixed coniferous and broadleaved forests, deciduous broadleaved forests, evergreen broadleaved forests, seasonal rain forests and rain forests occur sequentially from north to south. The precipitation in China mainly comes from the southeastern monsoon originating in the Pacific Ocean and from the southwestern monsoon originating in the Indian Ocean. The eastern and south central parts of China are moist and wet; the northwestern part is arid, but bordered by a transitional semi-arid zone of steppe vegetation. Forest, steppe and desert occur from east to west. More than two thirds of China is mountainous or high elevation plateau. The most extensive plateau, the Qing-Zang (Qinghai-Tibetan) Plateau in southwestern China, often referred to as the "roof of the world," strongly influences the geomorphology, climate and vegetation around the plateau (Chang, 1983). The mountains are dispersed throughout all of China and support vertical vegetation belts that reflect the latitudinal distribution of China's forests. Due to China's vast territory, climatic factors are various and geomorphological types are abundant providing rich and varied habitats for an abundance of plants and animals (Editorial Committee of Vegetation of China, 1980).

The status of China's forest types

China is a country with insufficient forests to meet the needs of its population of approximately 1.2 bil lion. The total forested area is 115.27 million ha with an average forest cover of about 12%. The largest forested area. of 10 million ha. is limited to Inner Mongolia and Heilongjiang provinces. The total forest cover in some provinces, such as Taiwan. Fujian. Zhejiang. Guangdong. Jiangxi and Jilin, ranges from 32% to 55%. North China was essentially a forested region in the past, but less than 10% of those forests remain, and there is not more than 4% forest cover in the provinces of Ningxia, Xinjiang, Gansu and Qinghai. Overall, the forested area in China is small and unbalanced in distribution. Of the remaining forests there is nearly an equal distribution between coniferous forests (49.8% of the total) and broadleaved forests (47.2%). Mixed coniferous and deciduous forests make up only 3% of the total forested area (Zhou & Li, 1990). Forests dominated by Pinus massoniana occupy the largest total area among the various coniferous forests. Forests of Larix spp., Cunninghamia lanceolata forests, Pinus vunnanensis forests and forests of Picea spp. also occupy large areas. The broadleaved forests comprise diverse types and can be classified in numerous associations.

The different forest types are distributed from north to south in China according to climatic zones. The mountains within each climate zone also support clearly defined vertically distributed belts of vegetation. Some forest types among the components of the vertical vegetation belts on some mountains can also be found within several climate zones.

(1) Boreal Forests

The boreal forests of China can be classified into 5 different forest types: 1) larch (Larix spp.) forests; 2) spruce (Picea spp.) forests; 3) fir (Abies spp.) forests; 4) pine (Pinus spp.) forests; and 5) Sabina spp. forests. These forests usually occupy cold, moist sites, usually on hills or on low to high mountains.

Larch forests. There are 10 species and 2 varieties of Larix in China, or more than half of all species of Larix worldwide. Nine types of larch forests are dominated by different species of Larix. Larch, an important timber tree in China, is characterized as a pioneer species in burned or cleared areas, and by species with seeds capable of being dispersed over long distances, the germination capacity of which is strong. Larch plantations are being developed rapidly in China (Zhou, 1991).

Spruce and fir forests. These two forest types are distributed widely in the northern hemisphere and are important components of boreal forests on the Eurasian continent. In general, they also form distinctive vegetational bands on mountains, have a wide distribution and provide large quantities of timber. Major spruce and fir forests in China can be classified into 26 types. Most are concentrated in the southwestern part of China, but some are in the northeastern regions of the country. Spruce and fir are shade plants, and may be replaced by birch and poplar forests after being felled. Natural regeneration is very difficult in cleared areas. For example, Picea meyeri forests were once found commonly in the Baihua, Donglin and Xiaowutai mountains of northern China, but only small areas of this type of spruce forest remain in nature reserves in the Guandi and Guanqin mountains. For the purposes of conservation and sustainable use of spruce and fir forests, selected felling and clearcut felling only in small areas has to be adopted so that sufficient seed resources can be preserved and adequate regeneration realized.

Pine forests. There are two types of pine forests in the cold temperate region of China, one with P. sylvestris var. mongolica, the other with P. pwnila. Forests of P. sylvestris var. mongolica occur in the northeastern part of China. The P. pumila forests are not extensive, occurring only in a narrow area along the top of the Great Xingan mountain range.

Sabina forests. Sabina forests are distributed only on the upper part of the mountains in southwestern China and should be given careful protection. Six types of Sabina forests can be found on sunny slopes between 2,800 and 4,500 m elevation.

(2) Warm temperate coniferous forests

Warm temperate forest types can be classified into Pinus tabulaeformis forests, Pinus densiflora forests, Pinus bungeana forests and Platycladus orientalis forests. Only the first is widely distributed. Most of the Pinus tabulaefonnis forests are concentrated in north China. Pinus densiflora forests appear on the Shandong and Liaodong peninsulas. Platycladus orientalis forests are widely distributed. but restricted to small areas. The distribution of Pinus bungeana is limited to northern China with disjunct populations in the southern part of Shanxi, western Hubei and northern Sichuan. Because of the effects of the dense population in northern China, natural pine forests have almost entirely disappeared and have been replaced by pure pine plantations. Pests and diseases are serious problems because of the simple structure of these monocultures and have caused a decrease in timber production. It has been suggested that broadleaved trees must be introduced into these pine plantations to increase the diversity. Hereafter, plantations should consist of mixed coniferous and broadleaved species to increase species diversity, enhance productivity and maintain stability (Institute of Botany, Chinese Academy of Sciences, 1990).

(3) Subtropical and tropical coniferous forests

Subtropical and tropical coniferous forests are abundant and can be classified into 27 types. Pinus tabulaeformis forests in the warm temperate zone are replaced gradually by P. massoniana forests in a southward direction. Pinus massoniana forests are distributed mainly in the eastern subtropical region of China. Pinus yunnanensis var. tenuifolia forests are found continuously in the western part of the subtropical region (Editorial Group of Vegetation of Yunnan, 1987). Pinus griffithii forests appear only in Tibet. There are many endemic coniferous forests with small areas of distribution in the southern part of China. Pinus armandii forests are concentrated primarily in this region.

Cunninghamia lanceolata, which grows rapidly and attains considerable biomass, is planted widely on acid soils in the southeastern subtropical area. However, degradation of the environment ensues when Cunninghamia is planted repeatedly on the same site. Mixed plantations with native broadleaved trees should alleviate this situation.

Cupressus funebris forests are distributed on limestone in the central part of the subtropical area. Forests with other species of Cupressus appear also on limestone mountains, but most of these have been destroyed or seriously altered and would be difficult to restore. Of the 12 species and one variety of the genus Keteleeria worldwide, all are endemic to China except for two species in Vietnam. Three species of Keteleeria form forests that are distributed mainly in the warm, moist, montane region extending southward from the Qinling mountain region in east central China. All original Keteleeria forests were destroyed, but restoration attempts have been successful.

It should be mentioned that in China there are specific coniferous forests consisting of so-called living fossils that have survived since the late Tertiary, or from even older geological periods. The species comprising these forests are Cathaya argyrophylla, Pseudolarix kaempferi, Metasequoia glyptostroboides, Giyptostrobus pensilis, Taiwania cryptomerioides and T. flousiana. These species occur independently of each other, all are dispersed in small isolated areas, and all appear to be gradually declining (for a discussion of the status of the largest remaining stand of Metasequoia see Bartholomew et al., 1983). Conservation measures and restoration efforts should be implemented to try to save and improve the condition of these few remaining relictual forests.

(4) Mixed Pinus koralensis and broadleaved forest

The mixed Pinus koraiensis-broadleaved forest is a major forest type in the eastern part of northeastern China. This forest type was once an important timber base, but nowadays areas forested with this association are severely limited. Perfectly conserved P. koraiensis-broadleaved deciduous forests occur mainly in nature reserves in the Xiao Xingan and Changbai mountains.

(5) Mixed Tsuga and deciduous and evergreen broadleaved forests

This type of mixed forest consists of Tsuga and deciduous and evergreen broadleaved trees, and is an important forest for water conservation. These forests are distributed from middle elevations to the subalpine zone on mountains covered by clouds and heavy fog in south central China. The areas occupied by these Tsuga-nmed broadleaved forests are so small that priority should be given to their preservation.

(6) Deciduous broadleaved forests

Deciduous broadleaved forests are widely distributed on hills and from mid elevation to subalpine zones on mountains in the temperate. warm temperate and tropical zones. The diverse oak forests and mixed oaks and deciduous broadleaved forests are typical of the warm temperate zone.

Oak forests are forests dominated by species of Quercus. There are about 11 types of oak forests extending frorn northern to southern China, each apparently dominated by a different species of oak.

The most noteworthy deciduous forests in China may be the beech (Fagus spp.) forests. Beech forests are also important deciduous broadleaved forests in Europe and North America. In China, beech forests occur only in mountains in the subtropical zone in the east central to south central part of the country. Mixed deciduous broadleaved forests, which are mesophytic forests, are now restricted to only small, isolated areas. They are distributed on slopes, usually along streams, and support a greater diversity of species than is found in oak forests.

There are nine types of birch forests in China, all distributed in mountainous regions. Three types of alder (Alnus spp.) forests occupy humid sites. Birch forests and poplar (Populus) forests are secondary forests that develop after montane broadleaved forests and coniferous forests are destroyed. In subtropical regions, deciduous broadleaved forests are secondary forests that develop mainly after the original evergreen forests are damaged. It must be mentioned that the wild apple forest in Xinjiang (Xinjiang Uygur Autonomous Region), in northwestern China, should be protected because of its uniqueness.

Deciduous broadleaved forests have been severely damaged in China. Large areas of forests have been superseded by shrublands or grasslands on mountains and hills. Of the surviving forests in remote mountainous regions, most are middle aged forests, since old growth forests disappeared long ago. Even now, deciduous broadleaved forests are still the target of exploitation for fuel, or are being replaced by pure plantations of coniferous species. Deciduous broadleaved forests are now doing poorly and are distributed as isolated islands. Although there are about 20 nature reserves comprising deciduous broadleaved forests, their total area is small. At present in China there are insufficient biosphere reserves to protect the full range of forest types that occupy the warm temperate zone.

(7) Evergreen broadleaved forest

Evergreen broadleaved forests are widely distributed in the humid subtropical zone in China. The subtropical region occupies a quarter of the total area of the country. There is a very rich diversity of plant species distributed throughout the evergreen forest area, including more than two thirds of the genera (2,674 of 3,980 genera) and one half of the species (14,600 of ca. 30,000 species for China as a whole) of spermatophytes. All evergreen broadleaved forests mentioned here are mixed forests dominated by several kinds of evergreen broadleaved tree species, without any apparent single dominant species. Each kind of forest is named for the characteristic species appearing within that forest type.

The typical evergreen broadleaved forests are most widely distributed in subtropical regions. They include all kinds of Castanopsis spp. forests, Cyclobalanopsis spp. forests, Lithocarpus spp. forests, Machilus spp. forests, Schima spp. forests, and so on. There is a slight difference between the easternmost and westernmost evergreen forests within China's subtropical zone. In the western part, the most widely distributed forests are Castanopsis delavayi forests and Cyclobalanopsis delavayi forests, but at relatively high elevations they are mainly Castanopsis orthacantha forests and Cydobalanopsis glaucoides forests. In the eastern part, there are more forest types, each with one of the following as the dominant species being widely distributed there: Castanopsis eyrei. Cydobalanopsis glauca, Castanopsis carlesii, Castanopsis fargesii, Machilus thunbergii, Schima superba.

Evergreen forests are precious forest types within China. Recently, however, there has been an apparent tendency towards replacing the evergreen forests with plantations of coniferous species such as Pinus massoniana and Chinese fir (Cunninghamia lanceolata). As a result, species richness within these areas has decreased enormously. Animals originally distributed in evergreen broadleaved forests have died out in many places because of a loss of suitable habitat. The establishment of nature reserves and biosphere conservation regions within the evergreen broadleaved forest zone is receiving more and more attention. Setting aside these areas is an effective means of in-situ conservation of biodiversity. Areas for particular reserves and methods of reasonable management still need further study.

(8) Sclerophyllous forest

In southwestern China, there are sclerophyllous forests with evergreen oaks as the dominant species. Sclerophyllous forests throughout the world exhibit a typical life form in response to climates with dry summers and rainy winters. Although that weather pattern does not exist in China, in southwestern China. especially in the mountainous region along both sides of the middle and upper reaches of the Jinsha river, there are large areas of Sderophyllous forests. The weather in this area is characterized by high precipitation in the summer and dry, cold winters. Compared with typical sclerophyllous forests, those in China are a special kind. They can be divided into nine types.

(9) Mixed deciduous and evergreen broadleaved forest

Mixed deciduous and evergreen broadleaved forests are typical of the northern part of the subtropical zone. In mountainous regions of the mid-subtropical zone, mixed evergreen and deciduous broadleaved forests are also distributed above the evergreen broadleaved forests. Because of differences in the availability of groundwater in the limestone regions of southern China there are several kinds of mixed evergreen and deciduous broadleaved forests. They are characterized by having various species of Cydobalanopsis as one of the dominants along with trees belonging to the Ulmaceae. These forests are mainly distributed on hills and on lower or middle elevation mountain slopes over exposed limestone. In the southern part of the subtropical zone these forests extend to elevations up to 2,000 m. These forests of the limestone mountain region should be carefully protected, because they are difficult to restore once they are destroyed.

(10) Tropical rain forest and seasonal rain forest

The tropical forests of China include rain forests and seasonal rain forests. Seasonal rain forests, which are seasonally wet or dry, are the most common kinds of forest on the margins of the tropical zone. The Chinese rain forests are an extension of the Indian and Malaysian rain forests and are distributed in areas with sufficient year-round rainfall and heat. But from the point of view of the distribution of the world's rain forests, those in China are situated at the northern edge of the range.

China has only a small area of tropical forest, but with 24 types composed of different kinds of tree species, mainly distributed in southern Guangdong, Hainan, southern Guangxi (Guangxi Zhuang Autonomous Region), southern Yunnan and southeastern Tibet. These forest types have the richest species diversity in China. From east to west the elevation at which rain forests occur changes as follows: in southern Guangdong and Hainan rain forests are found below 500 m; in southern Yunnan they extend up to 800 to 900 m; and in southeastern Tibet they reach 1,000 m. Of these regions, Hainan and southern Yunnan have more extensive rain forests than any other part of China. Unfortunately, with the expanding human population the extent of rain forest coverage and distribution in China has changed enormously. For example, the rain forest on Hainan covered 25.7% of the total island area in the early 1950s. Thirty years later, the coverage had decreased to 10.6%. Among the remaining forests, only 6% are natural. Xishuangbana in southern Yunnan is another area with large areas of rain forest. In the 1950s rain forest coverage was 55%. Now it is only 28%. Four hundred sites with rain forest, comprising a total area of about 40,000 ha, or only 2% of the total area of the region (Xishuangbana), are preserved by the local minority nationalities. Nature reserves occupy about another 12% of the region's total area. This means that only 14% of the original forest in the region is protected.

Among the seasonal rain forests, only Bombax malabaricum and Albizzia chinensis forests and Vatica astrolricha forests have a wide distribution. while other kinds of forests appear only locally. Among rain forests, the Vatica astrotricha. Heririera parvifolia. Hopea hainanensis forests, Antiaris toxicaria forests, and Dysoxylum gobara forests have only a small area of distribution in some valleys (Guangdong Institute of Botany. 1976; Editorial Group of Vegetation of Yunnan, 1987; Comprehensive Scientific Survey Team of Qing-zang Plaieau. 1985).

(11) Mangrove

Mangrove forests are specialized evergreen forests developed on tropical seashores in gulfs and estuaries below high tide line where the sea is relatively tranquil. Because of the wet habitat, we can call the tropical mangrove forests swamp forests of seashore saline soils.

Mangroves throughout the world are largely distributed between the Tropic of Capricorn and the Tropic of Cancer, but some extend to 32° N and 44° S. The world's mangroves have two centers of distribution: one in eastern Asia and the other in middle South America. The mangroves in eastern Asia are more vigorous and extensive. The Chinese mangrove forests are the same as others in eastern Asia. In China these forests are distributed mainly along the coast of the South China Sea, including Taiwan, the south part of Fujian, and the coast of Guangdong and Guangxi. Although the coastline of China is long and its area large, the area of Chinese mangroves is just 20,000 ha and their distribution is mainly on Hainan island and along the coasts of Guangdong. The mangrove forests in Guangxi, Fujian and Taiwan are secondarily important. The species composition of the mangroves comprises 21 families, 27 genera and 38 species. Nine species belong to the Rhizophoraceae. accounting for 54% of the total species of Rhizophoraceae in the world. There is about 85% similarity in species composition between the Chinese mangrove forests and the mangroves distributed in the Philippines and India. About 73% of the genera are the same as in Malaysia. The reasons for differences in species composition between the Chinese mangrove forests and the other eastern Asian mangrove forests is because of habitat differences within the range of mangrove distribution. Chinese mangroves can be divided into 19 types. Among them the Kandelia candel and Aeglceras corniculatum communities and the Rhizophora stylosa communities have the widest distribution, secondarily are the Avicennia marina communities. Sonneratia caseolaris communities also have a large area of distribution along the coast of Hainan island (Chen et al., 1988: Lin. 1990).

Discussion

The types of ecosystems in China are complex and comprise mostly forests distributed mainly in the eastern and south central parts of the country. Utilization of diverse ecosystems is necessary to satisfy the needs for food, limber, and other forest derived products required by a large population and for the development of industry and agriculture. By emphasizing the development of the economy and ignoring the conservation of the natural environment, and because of the lack of a strategy for the sustainable use of forest ecosystems. China has become a country of insufficient forest resources. As a result of the shortsighted practices of the past. many animals. plants and microorganisms have lost their habitat. Eastern China is the most developed economic region where forests were most seriously destroyed. Cities and towns were established on the plains and in the hills. Low mountains were reclaimed to provide farmland, orchards and tea plantations. Forests felled repeatedly for timber and fuel have been replaced by shrublands and grasslands which are often used as rangeland. Among the different kinds of forest ecosystems, the most threatened forests are various broadleaved forests and mixed Pinus koraiensis and broadleaved forests. The once large areas of the former have been replaced by pure coniferous plantations or farmland, orchards and rangeland. The deciduous broadleaved forests in north China were reclaimed for pine and larch plantations. Subtropical evergreen broadleaved forests were substituted with pure pine, China fir and bamboo plantations. The total area of the original tropical rain forests in China was very small, but because of economic needs large parts of them were displaced by economic plantations, such as rubber, coffee, etc.

On the other hand, even in regions of remote montane tropical rain forests, people using shifting agriculture techniques have caused the extinction of the original natural rain forest ecosystem. The original broadleaved forest ecosystems on hills and low mountains in warm temperate, subtropical and tropical areas have almost disappeared as well. Each type of forest ecosystem is composed of its own characteristic species. The extinction of any ecosystem means the extinction of characteristic species or genetic resources dependent on that ecosystem. It should be pointed out that the evergreen broadleaved forest ecosystems in the subtropical areas are the regions of megadiversity in China. They are characterized not only by an abundance of species, but also by major components consisting of endemic genera and species. Significant differences in the flora and fauna of the evergreen broadleaved forest ecosystems can be distinguished between the eastern and western parts of the subtropical zone. These are the most important ecosystems that should be conserved. Tropical rain forests and seasonal rain forests are valuable treasures. The rain forests on Hainan Island have been seriously devastated and much attention should be paid to their study and restoration. Small areas of rain forest and seasonal rain forests exist in the southern and southwestern parts of Yunnan Province, an area inhabited largely by local minorities. The traditions of the local minorities have preserved several original tropical rain forests in different areas (on Dragon Mountain. so-called by local people, for example) for religious reasons and as a result valuable biodiversity has been conserved.

The deciduous broadleaved forests are often ignored in China. and only a few secondary middle-aged ones are preserved in some nature reserves of small area; old-growth broadleaved forests are nearly extinct. The deciduous broadleaved forests, consisting of Quercus dentata and Q. variabilis have disappeared in the hills and low mountains; only low oak coppices with few species survive on the eroded hills. Mixed pine and broadleaved forests can only be found in the nature reserves of the Changbai and Xiao Xingan mountains. Spruce and fir, the dominants of boreal forests and the major timber trees, have encountered the same fate as other forests mentioned above. In brief, conservation and rational management of these forest ecosystems are important tasks that must be faced to preserve the remaining forest resources for sustainable use.

References

Bartholomew. B., D. E. Boufford and S. A. Spongberg. 1983.

Metasequoia glypnistroboides: its present status in central China. J. Arnold Arbor. 64: 105-128.

Chang, D. H. S. 1983.

The Tibetan Plateau in relation to the vegetation of China. Ann. Missouri Bot. Card. 70: 564-570.

Chen, S. P., Z. X. Liang and Y. Dong. 1988.

The Mangrove of the South Sea Coast. Guangxi Plant 8: 215-224.

Comprehensive Survey Team of Qing-zang Plateau, Chinese Academy of Science. 1985.

The Forest of Tibet. Science Press, Beijing.

Editorial Committee of Vegetation of China. 1980.

The Vegetation of China. Science Press, Beijing.

Editorial Group of Vegetation of Yunnan. 1987.

The Vegetation of Yunnan. Science Press, Beijing.

Guangdong Institute of Botany. 1976.

The Vegetation of Guangdong. Science Press, Beijing.

Institute of Botany, Chinese Academy of Sciences. 1990.

The Biological Ecology in Beijing-Tianjin Region. Marine Press, Beijing.

Lin, P. 1990.

The Proceedings of Mangrove, Xiamen University. Xiamen, Fujian.

Zhou, Y. L. and S. Y. Li. 1990.

The Forest of China. Science Press, Beijing.

Zhou, Y. L., ed. 1991.

The Vegetation of Great Xingan Mountains, Science Press, Beijing.