中国矮曲林的分布特征及生态意义

矮曲林是山地森林带在严酷的自然环境影响下发展演化而成的特殊植物群落,对中国山地植被和垂直带的研究具有重要的地理和生态意义。本文选择20世纪30年代以来在国内外文献中发表的52个矮曲林数据,结合Worldclim气候数据等,对中国矮曲林的类型和分布及其相应的气候条件进行了研究。结果表明：①中国的矮曲林主要包括山顶苔藓矮曲林、寒温性偃松矮曲林和岳桦矮曲林3类;其中,山顶苔藓矮曲林主要分布于秦巴山区以南的山地,而偃松矮曲林和岳桦矮曲林主要分布于东北地区。②山顶苔藓矮曲林主要由亚热带、热带地区的常绿阔叶林在山顶或山脊受山顶效应等的影响演化而来;而寒温性矮曲林主要由寒温性针叶林或针阔混交林在山顶或山脊条件下长期演化而来。山顶苔藓矮曲林自东向西随地势升高,其分布的海拔高度也逐渐升高;寒温性偃松矮曲林和岳桦矮曲林分布高度自南向北逐渐降低。③矮曲林分布在气候林线以下的山地,其气候条件足以支撑山地森林的发育,但由于山顶效应的存在(如强风、气候干冷或湿冷及土壤贫瘠等),只能发育矮曲林而非垂直地带性的山地森林。④中国东南部的很多山地高度小于3000 m,山顶效应明显,矮曲林广泛发育,造成了假林线的普遍存在。

Geographical distribution of cripple tree forest and its importance for forest line in China

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.