Northwest Sci-Tech University Of Agriculture And Forest Dissertation (Master)'s Degree

The seed plants from the middle-upper reaches of the Bailong River, as an independent floristic unit, were investigated and counted in view of taxonomy and floristic geography. On the basis of the modern geographic distribution patterns of all species, genera and family in this region, the geographic distribution types at the three toxonomic levels were identified and taken into statistical analysis. By three method of similarity analysis, the flora of middle-upper reaches of the Bailong River were compared with 10 adjacent regions to identify the relationships of floristic similarity among them. Also issue on the basic features, floristic properties and the principal origin of the floristic components in the middle-upper reaches of the Bailong River were discussed. The results were showed as follows:1. The flora of the middle-upper reaches of the Bailong River was consisted of 827 species of seed plants, belonging to 115 families and 519 genera, including 565 species of woody plants, which was 29.4% of the total number of Gansu Province. Also including 31 species of gymnosperm, belonging to 6 families and 14 genera. The species diversity of this flora was very abundant.2. There were many temperate genera and some tropical genera in this flora.The transition of the flora was obvious.3. The temperate families and genera occupied absolutely dominant position. The northern temperate elements were the core of the flora, and used to be the establishment species or dominant species.4. The flora contain both young elements and old elements.5. The origin of the flora was divided into three parts of Palaearctic continent element, Palaeantarctic element and Tethys sea element, the Palaearctic continent element was the main origin.6. The flora of middle-upper reaches of the Bailong River had the relationship in different degree with the adjunctive flora of the Taibai Mountains, the Zhongtiao Mountains, the Maxian Mountains, Yulong Mountains and the Tao River Basin. The relationship among the flora of middle-upper reaches of the Bailong River, Taibai Mountains and Tao River Basin was the nearest. The flora had higher similiarity in distribution types spectrum with Hengduan Mountains and Qin Mountains.7. There was the diversity of vegetation form in the middle-upper reaches of the Bailong River. The forest communities in middle-upper reaches of the Bailong River were divided into 6 vegetation forms, 11 formation-types and 68 formations.