Abstract: Southern Yunnan is located biogeographically at a transitional zone between tropical Southeast (SE) Asia and subtropical East Asia, and though far north of the Equator and at a relatively high altitude, has a rich and diverse tropical flora. The terminology used to describe the different tropical forest types in the region are confusing because the classification schemes used come from different disciplines. Using the classification scheme of tropical plant formations by Schimper (1903) and Richards (1996), which is based primarily on climatic factors, we discuss a new classification scheme of the tropical forests in southern Yunnan. Horizontal vegetation types in southern Yunnan are represented by tropical seasonal rain forests and monsoon forests. The tropical seasonal rain forest is a tropical Asian rain forest at altitudinal and latitudinal limits, while the monsoon forest is considered to be a transitional vegetation type between tropical rain forests and savannas based on their physiognomy and distribution. The monsoon forest is largely leafless during the dry season. The forests that occur on the middle and upper limestone slopes in southern Yunnan, which was called a monsoon forest in some Chinese botanical references, is reclassified as a seasonal moist forest. These forests are not equivalent to classical monsoon forests in their physiognomy, despite of the fact that it is affected by seasonal dryness and contains a high percentage of deciduous trees. The floristic composition also is different from monsoon evergreen broad-leaved forests in the region. This limestone forest, which abuts the seasonal rain forest on lower slopes and in the limestone valleys, is an altitudinal vegetation type on limestone bedrock in southern Yunnan.

Key words: Monsoon forest, Seasonal moist forest, Southern Yunnan