Introduction

Abstract

The region known as southwestern China (SW China, 21°08′32″-34°20′ N, 97°30′-110°10′ E) includes Yunnan, Sichuan, Guizhou provinces and Chongqing Municipality. Topographically, it lies between the first altitudinal step, the Tibetan Plateau, and the third step, the middle-lower Yangtze Plain, and stretches over a vast area (1,135,567 km²). The region includes the Hengduan Mountains, the Yunnan-Guizhou Plateau, and the Sichuan Basin. The Hengduan Mountain Range, situated at the juncture of Tibet, Sichuan and Yunnan in the southeast of the Tibetan Plateau, has an average elevation of 2,000–6,000 m. Its highest peak, Gonggashan, reaches 7,556 m above sea level. The climate is dominated by the Asian monsoon system. It falls into latitudes classified as subtropical, except for the small tropical area of southernmost Yunnan. With that exception, altitudinal climates range from subtropical to temperate, alpine and frigid.

The crust movements of various parts of SW China have undergone tortuous and complicated evolutionary processes over the long development of geological history. The most striking geological characteristic of the region is a massive crust movement strongly linked with the forming of the Hengduan Mountains – an extension of the eastern Himalayas.

The soils vary widely, including red earth, yellow, yellowish brown, brown, purple, and mountain gray-brown types.

In the Early Tertiary period, the areas now including eastern Yunnan, Sichuan, Chongqing and Guizhou bore subtropical dry and semi-dry sparse woodlands, while most areas now comprising Yunnan had a warm-rainy winter and hot-dry summer climate supporting subtropical evergreen broad-leaved forests. In the Late Tertiary period, the vegetation of SW China became a subtropical mixed evergreen and deciduous broad-leaved forest, except in southern Yunnan, home to a subtropical evergreen broad-leaved forest. In the Quaternary, vegetation changes were taking place at about 10,000 years BP (years before present), and by 7,000 years BP the pattern of the mixed evergreen and deciduous forest had become more complex. Parts of this region had not been covered by the ice sheet during the Quaternary. In general, since the Holocene, the natural vegetation types of SW China have been similar to those of the present time.

The rich flora and complicated plant geographic patterns of SW China result from a combination of elements from the Sino-Japanese, Sino-Himalayan, African-Mediterranean, and Indo-Malesian floristic regions. SW China is one of the most botanically diverse terrestrial regions on earth, with a high level of endemism.

The vegetation includes tropical rain forest, subtropical evergreen broad-leaved forest (the vast majority), warm-temperate deciduous broad-leaved forest, temperate coniferous and broad-leaved mixed forest, cold-temperate coniferous forest, alpine scrub community, meadow, and wetland, as well as thorny shrubland and savanna in hot-dry valleys. There are also precious remnants: Tertiary relict forests in specific habitats such as scree slopes, limestone areas and stream banks. The subtropical vegetation of SW China offers an unparalleled diversity of plant life and has far-reaching importance for the entire world.

In the last few centuries human activities have increasingly changed the subtropical vegetation. Man’s activities destroyed most of the original primary evergreen broad-leaved forests dominated by species of Cyclobalanopsis, Castanopsis, Lithocarpus, Machilus, Phoebe, Cinnamomum, Schima, Michelia etc. and they became restricted to remote mountain areas, nature reserves, steep slopes, and temple grounds. Complex mosaics of stands of varying ages, composition and structure intermingle with agricultural fields or mono-species plantations. So, SW China is truly a land of plant diversity, vegetation dynamics, and succession in time and space.