The Hengduan Mountains (simplified Chinese: 横断山脉; traditional Chinese: 橫斷山脈; pinyin: Héngduàn Shānmài) are a group of mountain ranges in southwest China that connect the southeast portions of the Tibetan Plateau with the Yunnan–Guizhou Plateau. The Hengduan Mountains are primarily large north-south mountain ranges that effectively separate lowlands in northern Myanmar from the lowlands of the Sichuan Basin. These ranges are characterized by significant vertical relief originating from the Indian subcontinent's collision with the Eurasian Plate, and further carved out by the major rivers draining the eastern Tibetan Plateau. These rivers, the Yangtze, Mekong, and Salween, are recognized today as the Three Parallel Rivers UNESCO World Heritage Site.
The Hengduan Mountains cover much of western present-day Sichuan province as well as the northwestern portions of Yunnan, the easternmost section of the Tibet Autonomous Region, and touching upon parts of southern Qinghai. Additionally, some parts of eastern Kachin State in neighbouring Myanmar are considered part of the Hengduan group. The Hengduan Mountains are approximately 900 kilometres (560 mi) long, stretching from 33°N to 25°N. Depending on extent of the definition, the Hengduan Mountains are also approximately 400 kilometres (250 mi) wide under the narrowest definition, ranging from 98°E to 102°E. The area covered by these ranges roughly corresponds with the historical region known as Kham.
The Hengduan Mountain system consists of many component mountain ranges, most of which run roughly north to south. These mountain ranges, in turn, can be further divided into various subranges. The component ranges of the Hengduan are separated by deep river valleys that channel the waters of many of Southeast Asia's great rivers. The core of the Hengduan Mountains can be divided into four major component ranges, described below.
The Hengduan Mountains support a range of habitats, from subtropical to temperate to montane biomes. The mountains are largely covered by subalpine coniferous forests. Elevations range from 1,300 to 6,000 metres (4,300 to 19,700 ft). The dense, pristine forests, the relative isolation, and the fact that most of the area remained free from glaciation during the ice ages provides a very complex habitat with a high degree of biological diversity.
The ecoregions that coincide with the Hengduan Mountains are:
Additionally, the lowest elevation portions of the Jinsha (Yangtze) River and Nu (Salween) River valleys in the southern Hengduan ranges are classified by the Chinese government as a tropical savanna environment, but this has not been recognized by the WWF.
The easternmost ranges of the Hengduan are home to the rare and endangered giant panda. Other species native to the mountains are the Chinese yew (Taxus chinensis) and various other rare plants, deer, and primates.