贺兰山植物群落类型多样性及其空间分异

THE DIVERSITY AND SPATIAL DISTRIBUTION OF PLANT COMMUNITIES IN THE HELAN MOUNTAINS

贺兰山是一座位于阿拉善高原与银川平原之间的高大山体 ,是我国西部温带草原与荒漠的分界线和连接青藏高原、蒙古高原及华北植物区系的枢纽。本文就贺兰山植物群落的类型多样性特征及其空间分布规律进行了分析 ,结果表明 :贺兰山植物群落有 11个植被型 5 5个群系。垂直分异明显 ,可划分成山前荒漠与荒漠草原带 (海拔16 0 0m以下 )、山麓与低山草原带 (16 0 0～ 190 0m)、中山和亚高山针叶林带 (190 0～ 310 0m)和高山与亚高山灌丛、草甸带 (310 0m以上 ) 4个植被垂直带。阴阳坡差异很大 ,在低山带 ,草原群落多占据阳坡 ,而阴坡则被中生灌丛所取代 ;在中山带 ,阴坡以青海云杉 (Piceacrassifolia)林为主 ,阳坡以灰榆 (Ulmusglaucescens)、杜松 (Juniperusrigida)疏林和其它中生灌丛为主 ;30 0 0m以上阴阳坡分异不明显。东、西坡及南、北、中段植物群落分异也很突出 ,各自均有一些特殊的群落类型。中段以森林和中生灌丛为主 ,南段和北段荒漠化程度较高 ,森林面积很小。北段有四合木(Tetraenamongolica)、沙冬青 (Ammopiptanthusmongolicus)、松叶猪毛菜 (Salsolalaricifolia)等特征群系 ,南段以贺兰山丁香 (Syringapinnatifoliavar.holanshanensis)、斑子麻黄 (Ephedrarhytidosperma)等群系最具特色。贺兰?

The Helan Mountains (38°10′-39°30′ N and 105°45′-106°45′ E) is situated on the eastern edge of the Alashan Plateau and the western edge of the Yinchuan Plain and extend about 270 km from north to south and about 20-40 km east to west. Its general altitude ranges from 2 000 m to 3 000 m with the highest summit at 3 556 m above sea level and relative elevations are 1 500-2 000 m. The Helan Mountains form an important boundary of climate and vegetation in northwest China: the eastern side of the Helan Mountains belongs to steppe climate and steppe vegetation and desert climate and desert vegetation characterize the west resulting in two different biomes. The mountains are a core area of the Alashan-Ordos biodiversity center that is among the top eight centers of biodiversity in China. It is a rich source of plants for the arid west and is an important pivotal point that connects the floras of the Qinghai-Xizang Plateau, the Mongolian Plateau and North China. Hence, it is very important to study the biodiversity of the Helan Mountains. The diversity and spatial distributional characteristics of plant communities are discussed in this paper. Based on our observations and research over many years, we have classified 11 vegetation types, and 55 formations in the Helan Mountains. The vertical zonation of the vegetation is strongly developed: vegetation belts can be divided into the desert belt (below 1 600 m asl), the steppe belt (1 600-1 900 m asl), the coniferous forest belt (1 900-3 100 m asl), and the alpine shrub or alpine meadow belt in the alpine or sub-alpine zone (>3 100 m asl). There also is a strong differentiation of vegetation on sunny and shady slopes. In the steppe belt of low hillsides, steppe communities inhabit sunny slopes but mesophilous shrub occur on shaded slopes. In the coniferous forest belt in the mid-elevation zone, the community of Picea crassifolia is distributed widely on shaded slopes but open forests of Ulmus glaucescens and Juniperus rigida or other mesophilous shrub occur on the sunny slopes. At 3 000 m and upwards, the vegetation of sunny and shade slopes is similar. The vegetation also is differentiated in an east-west and north-south direction resulting in some unique communities. The climate is warm and dry on the east side of the Helan Mountains and some thermophilic plants such as Zizyphus jujuba var. spinosa and Ostryopsis davidiana are distributed on the eastern side only. On the western side, the climate is cool and wet and there is a greater proportion of forests. The mid-elevation zone is the main body of the Helan Mountains, and the vegetation comprised primarily of forests and mesophilous shrub. The degree of desertification is very distinct in both the north and south segments of the mountains, but the communities are different. In the north, Ammopiptanthus mongolicus, Salsola laricifolia and Tetraena mongolica are dominant whereas Ephedra rhytidosperma, Syringa pinnatifolia var. alashanensis are dominant in the south. Furthermore, there are four endemic communities with Syringa pinnatifolia var. alashanensis, Ephedra rhytidosperma, Leptodermis ordosica and Hippolytia alashanensis in the Helan Mountains.