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

Based on the systematic sampling data, we analyzed and revealed the floristic characteristics and the relationships of floristic composition between and among the 11mountains on the Loess Plateau. The results indicate that:(1) The floristic composition in forest communities in the area is highly abundant. Among the 353 plots 1222 species of vascular plants, belonging 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 4families are Gymnospermae, and 34 species of 19 genera of 11 families are Pteridophyta.(2)Based on the region and local scale, the dominant distribution typesof floristic elements at the family and genus level are temperate origin, especially the north temperate origin. This characteristic is particularly obvious 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 level of floristic linkage by Hierarchical clustering. Through the comparison of maximum S?renson similarity coefficient,Helan Mountain, located in the northwest edge of the area, had the weakest relation with other mountains, whereas Taiyue Mountain had the strongest relation with all of the other mountains.(4) The results of multiple regression analysis accounted for 42.1% of the variation in the data, revealing a significant increase trend of the R/T value(ratio of the tropical to the temperate elements) with the rising at annual average temperature, whereas a contrary relationship with elevation, but not any significant tendency with annual precipitation.