黄土高原山地森林群落植物区系特征与地理格局

本文以样地数据为基础,对黄土高原内11座山地森林群落的区系组成、联系、格局以及与气候因子的关系等方面进行了较为系统的分析,结果表明：(1) 研究区内森林群落物种丰富,353个样地共调查到维管植物108科473属1222种,其中被子植物93科447属1179种,裸子植物4科7属9种,蕨类植物11科19属34种。(2) 按区域和局地两个尺度统计显示,研究区内科、属分布区类型以“温带分布”特别是“北温带分布”为主,此特征在群落尺度上尤显突出。(3) 非度量多维度标度排序 (NMDS) 第一轴主要揭示各山地森林分布的典型海拔变化范围,第二轴则展示出各山地的地理纬度位置关系;系统聚类树同样体现出各山地间基于区系组成特征的地理空间联系与南北位置关系,并将各山地依区系组成特征划分为4组;经比较山地间最大Sørenson相似性系数知,贺兰山因地处区域西北边缘而与其他山地间区系联系最弱,反之太岳山与其他山地区系联系最强。(4) R/T值 (热带属与温带属比值) 线性回归模型解释了42.1%的数据变异,并揭示该值随年均温升高呈显著上升趋势,随着海拔升高则有显著下降趋势,但与年均降水量之间并无显著趋势。

Floristic traits and geographic patterns of natural montane forests at community level on the Loess Plateau,North China

Based on the sampling data, we analyzed and revealed the floristic characteristics and the relationships of floristic composition between and among 11 mountains on the Loess Plateau. The results indicate that: (1) The floristic composition in forest communities in this region is abundant. Among the 353 plots, 1222 species of vascular plants, belonging to 473 genera of 108 families, were discovered. In those species, 1179 species of 447 genera of 93 families are Angyospermae, 9 species of 7 genera of 4 families are Gymnospermae, and 34 species of 19 genera of 11 families are Pteridophyta. (2) On the regional and local scales, the dominant distribution types of floristic elements at the family and genus levels are temperate origin, especially the north temperate origin. This characteristic is unique on the scale of community level. (3) The first axis of NMDS ordination revealed typical variation range of elevational gradient. The second axis displayed the latitudinal relationship between and among different mountains. The whole study area can be divided into 4 groups with different levels of floristic linkage by hierarchical clustering. Through the comparison of maximum Sørenson similarity coefficient, Helan Mountain, located at the northwest edge of the region, had the weakest relation with other mountains, whereas Taiyue Mountain had the strongest relation with all of the other mountains. (4) Multiple linear regression analysis accounted for 42.1% of the variation within the R/T value (ratio of the tropical to the temperate elements), revealing a significant trend that the R/T value in the region increased at sites with high annual average temperature, whereas it decreased at sites with high elevation. However, no significant tendency of the R/T value with annual precipitation was found in the same analysis.