The Floristic Geography Of Vascular Plant In The Loess Plateau Of Northern Shaanxi Province

The vascular flora of the Loess Plateau of Northern Shaanxi Province (LPNS), one of the important components of Loess Plateau flora, was first analyzed as a whole object. Based on the great scale investigation and a large amount of references, adopting the theories and methods of the related disciplines like Floristic Geography, Biodiversity Protection and Utilization, Plant Ecology, etc., this paper studied the flora in the LPNS, including the floristic composition, characteristics, endemism, substitute phenomenon, geographical correlations, origination, evolution and development, floristic zoning and spatial distribution characteristic, plant biodiversity of typical valleys, flora of typical plant communities, protective plants and resources plants, and put forward measures for protection and sustainable development. The main achievements are summarized as follows:1.The characteristics of the floristic composition(1) The species of this area are comparatively rich and the species density high. There are 1 413 species (including infraspecies taxon) of vascular plants belonging to 140 families and 572 genera in the LPNS. The family, genus and species number of this region account for respectively 71.3%, 62.4%, 41.4% of that of the Loess Plateau. There are 63 species of fern belonging to 32 genera in17 families, and 1 350 species of seed plants belonging to 542 genera in 123 families. The species density of vascular plants is 1.52 species /100km2.(2) The dominance of vascular flora in the LPNS is comparatively strong, and the characteristic (or typical) taxa are comparatively rich. There are 26 dominant families, 23 dominant genera, 9 characteristic families, 24 characteristic genera, and a larger number of dominant or characteristic species.(3) The mono-species or minor-species genera are comparatively rich. There are 30 mono-species and 45 minor-species genera of the flora in the Loess Plateau of Northern Shaanxi Province. The life forms of these genera are mostly herbage, the areal types aremainly East Asia, Ancient Mediterranean, Old World Temperate and Endemic to China.2.The life forms and ecological types of the seed plants are various, with life forms including arbor, shrubbery, herbage (including the annual, biennial and perennial), liana etc. and the perennial herbage plays a dominant role. The ecological types include the aquatic, the hygrophyte, the Hygro- mesophyte, the Mesophyte, the Xero- mesophyte, the Meso-xerophyte and the Xerophyte and the mesophyte plants play a dominant role.3.About the characteristics of the floristic areal types.(1) The floristic elements are comparatively complicated and diverse and are extensively related to other areas.(2) The flora features a clear transitional and temperate character. The flora of LPNS is influenced and penetrated, geographically and genetically, in many aspects. Therefore, it has developed rich floristic elements, with distinct aggregation, penetration and mixture to show its strong transitional features.(3) Tropic flora affect to a certainty on the LPNS's flora, and indicate the relation of origin of the LPNS's flora with tropic area.4.The endemism and substitute phenomenon of the flora(1) There aren't the families endemic to China in this region. But there are 4 families endemic to East Asia, mostly relic taxa. The genera endemic to China and the species endemic to Loess Plateau of Northern Shaanxi Province are comparatively poor, but the species endemic to China are rich.(2) The gradient change of plants from south to north of the area is outstanding, and some plants take clearly on geographical substitute phenomenon.5.The flora has not only an ancient origin, but also younger elements6.Relationship to the flora of other areas(1) The comparison of R/T value (the proportion of tropic genera to temperate genera) between LPNS and other areas reflects the ecological features and differences of the locations.(2) The flora of LPNS is found to be closely relation to the flora of the mountainous regions in Hebei and Beijing, and is also somehow related to the flora of Inner Mongolia, Shanxi and Ningxia.(3) On a larger scale, the flora of LPNS (especially South LPNS) is closely related to North China. The flora of North LPNS is very closely related to Mongolia grassland while the flora of the district of Huanglong Mt. and Guan Mt. is closely related to North slope of Qinling Mts., and is somehow related to Southwest China, Central China, East China and Northeast China.7.Sources and evolution of the floraAfter a comparative analysis of the paleobotany documents and present flora of the Loess Plateau of Northern Shaanxi Province (LPNS), the evolution and sources of LPNS's flora are studied. The evolution of flora over all the stages since the Cretaceous period are discussed. From the flora evolution and the spore and pollen comparison between the modern and the Cenozoic period, it is believed that the flora of LPNS can be dated back to four major sources:(1) the local and neighbouring flora in the late Cretaeous period and Paleogene, with some herbaceous plants and hygrophytes originating in the Neogene and the hardy and drought enduring plants in the Quaternary period.(2) the Mediterranean, Central Asia and the Eurasian Steppe.(3) the Northeast Asia, the temperate and cold area of Siberia.(4) the Southwest China, Northwest China, North China, and the Qinling Mts. and Central China.8.The floristic zoning and spatial distribution(1) The flora of the area is divided into 2 plant provinces, namely North Plant Province of the LPNS and South Plant Province of the LPNS, and 4 districts: a. the grassland district of the sandy and windy area along the Great Wall; b. the shrubbery and grassland district in the loess hilly and gully area of the LPNS; c. the district of Ziwuling Mts. and Lao Mt.; d. the district of Huanglong Mt. and Guan Mt..(2) The plants of the LPNS features clear difference of spatial distribution, the richness of plants species of the 4 districts is obviously different. The district of Mt. Huanglong and Mt. Guan is richest, while the grassland district of the sandy and windy area along the Great Wall is the poorest.(3) Comparison of the flora species development. The differentiation of plant genera and species in the south LPNS is comparatively intense compared with North of LPNS. The differentiation comparison of plant genera and species of the 4 districts finds that the district of Huanglong Mt. and Guan Mt. is more intense, while the grassland district of the sandy and windy area along the Great Wall is comparatively low.9.The plant biodiversity of typical valleysThe Zhifanggou valley which was enclosed over 30 years ago was compared with Xiannangou valley enclosed in recent years in terms of the flora, life forms, ecological types, diversity of vegetation types, quantitative index of main plant community and species diversity of main plant community, etc.. The result are as follows: (1) the floristic species components of both the valleys are hardly different. (2) the plants communities of Zhifanggou Valley are not only diverse, but also extensively distributed and mostly composed of mesophyte communities. In contrast, the community number of Xiannangou Valley is small and most of the communities grow within a limited area. This valley is composed mainly of Xerophyte plants. some mesophytes are even disappearing from this valley.(3) The edificato height, richness (piece/m2) and coverage of the major communities in Zhifanggou are obviously higher than that of Xiannangou.(4) the mesophytes account for a higher proportion in the major communities of Zhifanggou and the xerophytes account for a smaller proportion.(5) in a same community, the nanophanerophytes, chamaephytes, hemicryptophytes and the interlayer plants accounts for a higher proportation in Zhifanggou, compared with Xiannangou, while hemicryptophytes the annual herbage plants account for a smaller proportion.(6) To the same community, the species richness, diversity and evenness of the Zhifanggou are generally higher than that of Xiannangou.10.The typical plant community floraComparison study on the flora of Quercus liaotungensis community was done between the LPNS with Qinling Mts. The result shows that there are 51 species of vascular plants belonging to 42 genera of 27 families in the LPNS, and 67 species of vascular plants belonging to 60 genera in 31 families in Qinling Mts.. the richness of plants species of Quercus liaotungensis community in the LPNS is poor and community structure simple. In addition, the similarity coefficient of Quercus liaotungensis community in the two areas is low. Studies on the floristic elements of plant genera and species were carried out to find that the Quercus liaotungensis community in both areas belongs to the temperate, and the endemic species to China in Quercus liaotungensis community of both areas are more in common with North China, less with Southwest China, Center China, East China and Northeast China.11.The rare and endangered plants.(1) The rare and endangered plants are comparatively rich in the LPNS. There are 75 species of protected plants, belonging to 63 genera of 44 families, among of which 35 species are the state protected plants, and 7 province protected plants and 33 regional protected.. According to endangered ranking system, these plants fit into 3 ranks, namely EN, VU and NT, and accordingly three protection levels. Therefore, these plants consist of 15 species of EN, 20 species of VU and 40 species of NT, 39 species of level one protection, 17 species of level 2 protection and 19 species of level 3 protection.(2) The areal types of the protected plants are mainly the elements of North Temperate, Old World Temperate, East Asia and Endemic to China, with the North Temperate elements dominating. The floristic elements of the protected plants are mainly Endemic to China, Temperate Asia and East Asia while the Endemic Species to China in the LPNS plays a dominant role, which are mainly composed of elements of North China, Endemic Species to LPNS and Southwest China-Center China-North China.12.The resource plants are rich. There are about 950 species which can be classified into 14 types by their use.