Mountains of Southwest China

David E. Boufford⁹⁴, Peter Paul van Dijk⁷¹ and Lu Zhi⁷²

The Mountains of Southwest China Hotspot, perhaps more appropriately referred to as the Hengduan Shan, covers the temperate to alpine montane region lying between the easternmost edge of the Qinghai-Xizang (Tibetan) Plateau and the Central Chinese Plain. It lies to the north of the Indo-Burma Hotspot, and to the immediate east of the Himalaya Hotspot, and is bounded to the northwest by the dry Qinghai-Xizang Plateau, to the north by the Tao River of extreme southern Gansu, and to the east by the Sichuan Basin and the plateau of eastern Yunnan.

The hotspot is characterized by extreme topography of steep, often precipitous mountains, with altitudes ranging from less than 2 000 m in some valley floors to 7 558 m at the summit of Gongga Shan. The mountain ridges are oriented in a generally north-south direction, perpendicular to the main Himalayan chain. The region includes the Hengduan Shan, Gaoligong Shan, and Nu Shan mountains of western Yunnan; the Nyainqentanglha Shan, Ningjing Shan, Taniantaweng Shan, and others at the southeastern edge of the Qinghai-Xizang Plateau; the Shaluli Shan, Daxue Shan (including Gongga Shan), Chola Shan, and Qionglai Shan mountain systems of Sichuan; and the Min Shan on the Sichuan-Gansu border. The Ailao Shan and Wuliang Shan of central Yunnan are not part of this hotspot (being instead included in the Indo-Burma Hotspot). The total surface area of the Mountains of Southwest China Hotspot (which, according to the delineation of WWF ecoregions, results in the exclusion of some high-altitude regions that we include here) is approximately 262 466 km².

The complex topography of the region results in a wide range of local climatic conditions. Correlated to altitude, latitude, and exposure, temperatures range from frost-free throughout the year in parts of Yunnan and short, frost-free periods at the northern boundary of the region, to permanent glaciers on the high mountain peaks of Sichuan, Yunnan, and Xizang. Annual average rainfall in the region exceeds 1 000 mm on southwestern slopes at higher altitudes in Yunnan, while areas of the northwestern part of the region, in the rainshadow of the Qinghai-Xizang Plateau, rarely receive more than 400 mm annually.

Given the wide range of topographic and climatic conditions, the mountainous area of western Sichuan possesses a great variety of vegetation types. These include broad-leaved and coniferous forests, bamboo groves, scrub communities, savanna, meadow, prairie, freshwater wetlands, and alpine scrub and scree communities (Sichuan Vegetation Study Group 1980). Furthermore, as a result of the complex local geomorphology, the north-south orientation of the mountains, and the huge vertical differences in topography, vertical zonation of vegetation formations is also well developed. The extremes of topography, vegetation, and climate, coupled with the isolation of the numerous steep peaks and ridges – like islands in the sky – have served as a stimulus to evolution, and are responsible for the high species diversity and endemism of plants, vertebrates, and invertebrates found in the region.

Vascular plant diversity is particularly impressive in this hotspot, with the mountains of western Sichuan, Yunnan, and southeastern Xizang being home to as much as 40% of the total for all of China, or about 12 000 species. Of these, about 3 500 species (29%) and at least 20 genera are endemic, including about 100 endemic ferns. More than a quarter of the world's Rhododendron, Primula, Corydalis, Anaphalis, Delphinium, Gentiana, Saussurea, and Sorbus species occur in the Hengduan Mountains of western Sichuan, while over half the species of Ligularia, Cremanthodium, Cotoneaster, and Pedicularis have been recorded in this hotspot. Of particular interest is the occurrence of two endemic families, Circaeasteraceae (two genera, Circaeaster and Kingdonia) and the monotypic Acanthochlamydaceae (Wu 1988; Xiong 1989; Xu 1991; Wang et al. 1993, 1994; Zhou 1994).

In terms of vertebrate diversity, some 237 mammal species occur in this hotspot, of which only five are endemic. For a relatively poorly known region, this hotspot has some of the world's most interesting and bestknown flagship species, of which the giant panda (Ailuropoda melanoleuca, EN), perhaps the world's number one wildlife symbol, is the most famous. At present, this species survives in fragmented populations confined to over 40 reserves stretching from western Sichuan to southern Gansu and southern Shaanxi. Other important mammal flagships include the golden monkey (Rhinopithecus roxellana, VU) and the Yunnan or black snub-nosed monkey (R. bieti, EN), which lives at higher altitudes (as much as 4 500 m) than any other nonhuman primate; the takin (Budorcas taxicolor, VU), a 300-kg goat-antelope with a coarse, dense brown coat; and Bailey's goral (Nemorhaedus baileyi, VU), a goat species endemic to the Gaoligong Shan.

The bird fauna of the Mountains of Southwest China Hotspot is quite rich, with 611 species recorded, including residents, migrants, and vagrants. Of these, only a single species is endemic. No fewer than four Endemic Bird Areas (EBAs) have their boundaries largely overlapping with this hotspot (Stattersfield et al. 1998). A recent study by Lei et al. (2003) has confirmed that the Hengduan Shan is a center for avian endemism. This region also has the world's richest variety of pheasants and their relatives, with 27 species inhabiting the hotspot, among them the Lady Amherst pheasant (Chrysolophus amherstiae). For sheer brilliance, however, nothing exceeds the iridescent splendor of two monal pheasants, Sclater's monal (Lophophorus sclateri, VU) and the Chinese monal (L. lhuysii, VU).

The hotspot's herpetofauna is surprisingly diverse, given the generally temperate climate and the physiological constraints on ectothermic animals. In all, this hotspot is inhabited by about 94 reptile species, of which 15 are endemic; amphibians are represented by around 98 species, of which 40 are endemic. Particularly remarkable among amphibians are the radiations of two closely related megophryid frog genera, Scutiger and Oreolalax; of the 12 species of the former that are present, nine are endemic, while all 11 species of Oreolalax present are endemic (70% of the entire genus). Some of these species occur at relatively high altitudes; for example, the Xizang alpine toad (Scutiger boulengeri) is found to elevations of more than 5 000 m above sea level.

The Mountains of Southwest China are important because they feed the most species-rich river systems in Asia, including both temperate and tropical examples. Major river systems that traverse or originate in the hotspot include the Jingshajiang, Yalongjiang, Daduhe, and Minjiang, all branches of the Yangtze River leading to the East China Sea, while Lancangjiang (Mekong River), which passes through Guangxi Province, Laos, Cambodia, and Vietnam, leads to the South China Sea. Nujiang reaches the Indian Ocean through Guangxi Province and Burma. Within the hotspot itself, the fish fauna comprises 92 species, of which 23 species and two genera are endemic. The fish fauna is represented mainly by species of the families Cyprinidae (50) and Balitoridae (18), while the endemic species are predominantly in two genera: Schizothorax (eight) and Triplophysa (three).

Despite the inaccessibility of much of the region, the major threat to biodiversity in this mountainous hotspot before 1998 was commercial logging. Overall forest cover in Sichuan, one of China's main sources of timber, declined from 19% in the 1950s to 12.6% in 1988 (Smil, 1992). Almost all this loss has been in the more remote and mountainous western part of Sichuan, since forests elsewhere in the province were cut long ago (MacKinnon et al. 1996). Removal of trees is not limited to timber species. 1998 saw the launch of a national logging ban by the government, since which commercial logging has ceased. However, forests are still being cut at a significant rate for fuelwood and house construction by local residents who live in alpine areas in the hotspot. The high valleys are bitterly cold in winter and transportation facilities are limited, so local collection and stockpiling of firewood is essential. In recent years, as economic conditions have improved, houses built by local villagers have been getting bigger and bigger, and it is estimated that each consumes nearly 300 m³ of timber per year. The volume of firewood collected and timber cut for house construction may exceed past logging harvests in some areas and is a primary cause of deforestation today (MacKinnon et al. 1996). Furthermore, nomadic Tibetans wander throughout the entire region with their herds of yak, sheep, and goats to utilize the natural pastures. Traditionally, they ascend to alpine pastures in summer and return to valleys before winter. Nearly all areas without natural forest cover, or unsuitable for crops, are heavily grazed by livestock, the only exceptions being scree slopes and vertical cliffs (MacKinnon et al. 1996).

Looking at what remains in terms of natural vegetation, MacKinnon et al. (1996) calculated that remaining areas of forest covered 23% of Yunnan Province, 12% of Sichuan Province, and 5.1% of Xizang Province in 1992. The forest cover figure for Sichuan is probably still a reasonable estimate for the entire hotspot, although much of the region has not been covered by forest since the Himalayan uplift. However, the intensity of grazing has had a conspicuous impact nearly everywhere, to the point that it is difficult to know what exactly constitutes natural vegetation. Certainly, less than 10% of the entire hotspot area is in pristine condition, and quite likely it is as low as 5%-6%, although, for purposes of this analysis, we use an estimate of 8% remaining. Since the 1980s, and particularly from the late 1990s onwards, forest regeneration has been taking place on logged sites and “wasteland.” While the forested areas have increased, another threat has arisen in the form of monoculture plantations, sometimes with alien species such as Eucalyptus.

Over 150 protected areas covering more than 70 000 km2 have been declared in the area that is included here in the hotspot. The region's most famous protected area is Wolong Nature Reserve in western Sichuan, which covers about 2 000 km². Included in the list of protected areas are 28 nature reserves designated for giant panda conservation, totaling about 16 800 km²; these reserves account for nearly half of all forest land under protection in this hotspot. Interestingly, Wolong has a great diversity of ancestral species from which many fruit trees and shrubs were domesticated, such as apples, pears, plums, cherries, gooseberries, black currants and strawberries, representing a genetic resource of inestimable value (Mackinnon 1996)). In total, 4 000 plant species occur in the reserve, including many rare, endemic, and otherwise notable species such as Tetracentron sinense, Chinese yew (Taxus chinensis), and Chinese katsura (Cercidiphyllum japonicum var. sinense) (Zhao et al. 1990).

Other important protected areas in the hotspot include: Emei Shan, an isolated limestone mountain on the eastern edge of the hotspot that rises to 3 099 m in height, is considered to be one of the botanically richest and most diverse mountains in the Northern Hemisphere, and also harbors an important population of the Tibetan macaque (Macaca thibetana), being one of the few places where these animals can readily be seen; Luo Ji Shan Nature Reserve, which contains more than 2 000 species of higher plants, including more than 50 species of Rhododendron; and Gaoligong Shan Nature Reserve. The expansion of Gaoligong Shan (4 052 km²) northwestward into Xizang and eastward across the Nu Jiang (Salween) and Lancang-Jiang (Mekong) rivers to link with the Bai Ma Xue Shan Nature Reserve (2 816 km²) and the east bank of Jinsha River (part of the Yangtze) has created the famous Three Parallel Rivers World Heritage Site, which provides protection for the many different ridges and valleys and their highly distinctive floras.

Although some important areas are currently protected in this hotspot, much more needs to be done. The enormous watershed value of this region in and of itself provides more than adequate justification for increased protection. Furthermore, the scientific importance of this hotspot can hardly be overestimated, since it provides a living laboratory for the study of biogeographical patterns and evolutionary processes critical to evaluating hypotheses on the diversification of plants and animals.

In spite of the importance of this hotspot, time is short. The many old pressures on fragmented natural habitats from grazing, clearance, hunting, and collection of forest produce remain, and new threats, such as dam building on all main rivers in the hotspot, mining, and unplanned mass tourism development accompanied by road expansion and wildlife consumption are emerging. This means that the extinction of many of the restricted-range species of plants and animals is a realistic and immediate possibility. Since the late 1990s, the Chinese government has implemented intensive land protection policies in the hotspot area, including the logging ban, the Grain to Green Project (conversion of sloping farmland to forest and grassland, under way in the provinces of Sichuan, Shaanxi, and Gansu), and the Endangered Species and Protected Areas Program, along with the financial investment of billions of dollars. Many new protected areas have been planned. NGOs, working with the government, have also made significant contributions in this great movement, especially on capacity building and applied research to provide a sounder scientific basis for both conservation and development policies, designation of protected areas, and the use of local plant and animal resources.

One other significant feature of this hotspot is its rich cultural diversity. There are 16 ethnic groups living in this area, and the majority of the region is inhabited by Tibetans. In Tibetan culture, sacred landscape is a traditional land protection system that still exists today. Thousands of villages and monasteries each have their own sacred site – mountain, lake or forest – where oldgrowth forests can be found. However, this tradition has been challenged by outside influences and the demand for economic development. Preserving and reviving such a tradition will provide much impetus to protect the biodiversity in this hotspot.

< previous section  < index >  next section >