关键词: 山顶苔藓矮曲林, 偃松矮曲林, 岳桦矮曲林, 林线, 分布特征, 山顶效应

Abstract:

Cripple trees that often lie between the upper montane forest and the alpine belt and normally grow at isolated summit locations or mountain ridges is a type of vegetation community shaped by the severe environmental conditions or the summit syndrome. The classification of cripple trees and their geographical distribution are important for the study of mountain altitudinal belts and mountain environment. Based on 52 cripple-tree datasets published in the literature since the 1930s and the climate data of Worldclim, this study analyzed the spatial distribution characteristics of cripple trees in China and their importance for identifying forest lines. The results show that: (1) Cripple trees in China are mainly consisted of mossy cripple trees and cold temperate cripple trees (including the Pinuspumila cripple trees and the Betulaermanii cripple trees). The Qinling-Daba Mountains are the boundary between mossy cripple trees and cold temperate cripple trees. Mossy cripple trees are distributed to the south of the Qinling-Daba mountain area, and cold-temperate cripple trees are distributed in northeast China. (2) With the increase of relief from east China to the west, the distribution altitude of mossy cripple trees increases gradually. The distribution altitude of mossy cripple trees on the southeast coast of China (Guangdong, Fujian, and Zhejiang) is about 800~1200 m, and west into the inland region such as west Zhejiang, Anhui, Jiangxi, Hubei, and Hunan, the altitude increases to about 1000~1800 m; in Chongqing, Guizhou, and Yunnan, the altitude increases to about 1500~3000 m, and higher than 3000~4500 m in the southeast of the Tibetan Plateau and the Himalayas. (3) The distribution altitude of the cold temperate cripple trees decreases from south to north. The distribution altitude of the Pinuspumila cripple trees decreases from 1400~1520 m at the Aokulidui Mountain to 1240 m at the Baikalu Mountain in the Greater Khingan Range; the altitude of the Betulaermanii cripple trees decreases from 1800~2100 m at the Changbai Mountain to 1100~1300 m at the Lesser Khingan Mountains. (4) The summit syndrome (strong winds, lower temperatures, and poor soils on the mountain summits or ridges) controls the formation of cripple trees. Mossy cripple trees are evolved from the subtropical montane evergreen broad-leaved forests or the tropical montane monsoon evergreen broad-leaved forests under the influence of the summit syndrome, and cold temperate cripple trees are evolved from the cold temperate coniferous forests or the coniferous and broad-leaved mixed forests in China under the influence of the summit syndrome. (5) The distribution altitude of cripple trees is often lower than the location of the forest climate line; their lower limits are not real forest line or climate forest line. Temperature in the warmest month (July) and annual precipitation for the distribution area of cripple trees (greater than 10°C and above 500 mm) verify that the climate condition of the cripple-tree distribution area can be suitable for forest growing. Most mountains in southeastern China are lower than 3000 m and cripple trees are present under the influence of the summit syndrome, therefore the forest lines in southeast China normally are not the real forest lines.

Key words: mossy cripple trees, Pinuspumila cripple trees, Betulaermanii cripple trees, forest line, geographical distribution, the summit syndrome