Vertical vegetation zones along 30 degrees N latitude in humid East Asia

Structural changes in altitudinal vegetation zones along a 30 degrees N parallel were studied based on vegetation data from 20 mountains in East Asia, from 85 degrees E to 130 degrees E longitude. The altitude of comparable vegetation zones showed a sharp increase of 1400-1900 m from east to west. Forest limit reached an altitude of 4400-4600 m in the eastern Tibetan Plateau, being the highest forest limit in the world. The limidng factor for the upper limit of a vegetation zone was different in the east and west. Low temperature in winter controlled the upward distribution of the evergreen broadleaf forest in the east, whereas the limiting factor was growing season warmth in the west. A close correlation was found between the climatic indices and annual range of monthly mean temperature (ART) at the upper limit of a vegetation zone. Component genera of each vegetation zone along the 30 degrees N parallel were analyzed, and it was found that the alternation of component genera from east to west was much more apparent in cool-temperate forests, reflecting their response to macrotopography and air masses. The distribution of Fagus extended into winter-cold regions, whilst Tsuga occurred principally in oceanic and warm climates. The northern limit of Tsuga corresponded well to an ART isotherm of 23 degrees C and its southern limit coincided with that of Fagus. According to the distribution of Fagus and Tsuga, the cool-temperate forests in East Asia along the 30 degrees N belt were divided into three types: deciduous broadleaf forest (represented by Fagus), mixed forest (dominated by Fagus, Tsuga and others), and mixed evergreen forest (consisting mainly of Tsuga and sclerophyll oaks).