Study On The Altitudinal Differentiation Of Seed Plants Flora In Baishuijiang National Reserve In Gansu Province

Baishuijiang National Reserve is located in Wenxian and Wudu of Gansu province,which reaches from 104° 16' to 105° 27' E., and from 32° 16' to 33° 15' N. with an area of 2137.5 km2.The highest peak is about Alt. 4070m,and the altitude range is 3490m.The reserve has a rather rich flora which is composed of 1970 species (including varietes), 718 genera and 183 families of seed plants.Being At the transitional zone from north subtropic to south warm temperate and near to Qinling, Central China,Qinghai-Xizang plateau and Hengduan mountain region,the reserve is an important region of floristic studies. The region's altitude range is rather wide, thus the climate, soil and vegetation of each verdical zones differ obviously, and the floristic components and characters are influenced intensively.Based on Baishuijiang National Reserve Seed Plants Flora Database, the flora is analyzed with holistic-verdical dimensions and the main results and arguments as below:1.The species,genara and families in this flora are very abundant,and the floristic composition is rather complex.Analysis of families and results: 1) The tropical families is more than temperate ones(73:61),which shows consanguineous relationships with tropical floras. 2) The analysis based on three systems of the angiosperms reveals that there are lots of primitive families or basal families suggesting the ancient origin of the flora.Analysis of genara and results: 1) According to the ratio of tropic-genara / temperate-genara (0.45), the flora is of temperate nature mixed some subtropic characteristics.2) The resever has lots of primitive genera which demonstrate further that the flora is rather ancient.3) The region is rich in single-mode genera (371 g.) and minority-mode genera (265 g.) that are much older or more isolated systematically. 4) Sharing many endemic genera to China with Qinling,Hengduan Mountain and Central China,the flora has close relations with those floras.Analysis of areal-types of species shows that East Asia,Central China and Hengduan Mountain floristic elements hold prominent positions and South China,North China,Tropical Asia,North Temperate elements account for some proportion.These phenomena indicate that several floras intercross and penetrate reciprocally in this region.2.In the family level,verdical distribution of each family is relative to its floristic characters.Verdical ranges of tropical families and their concentrating zones is lower than temperate ones,but many families are exceptive.The families that approach distribution border in the reserve exist in medium-low altitude belts strictly.According to illustration of "altitude-floristic elements",the verdical distribution pattern of Pantropic families,Trop.Asia ones,North Temp, ones corresponds to environmental gradient.The floristic equilibrium point between the tropical families and the temperate ones is roughly located at the altitude of 1500m.The Alt. 2500m is the line at which family-grade floristic structure changes intensively.According to the floristic component and characters of family level,we propose that the region can be divided into 4 sections:<1200m,1200~2500m,2500~3500m,>3500m.The belt 1000-1100m is the significative belt in the family level.3.In the genus level,dominant groups obviously vary along with the altitude gradient.For instance,the tropical dominant genera absolutely disappear above Alt. 2000m.Compared to the family level,the vertical differentiation of floristic elements in genera level correspond more acutely to environmental gradient.Most groups' altitude distribution is consistent with their ecological characters.Vertical distribution of East Asia genera is influenced both by modern environment and the geologic history.Alt. 2500m is a breakpoint at which genus-grade floristic structure varies intensively.According to the floristic component and characters of genera level,the region can be divided into 4 sections:<1600m, 1600~2500m, 2500~3500m,>3500m.The belt 1500-1600m is the significative belt in the genus level.4.In the species level, the vertical distribution of Pantropic,Tropical Aisa,Central China,South China,North Temp.,Qinghai-Xizang region,Hengduan Mountain elements corresponds with the vertical climate spectrum of this mountain.The previous 4 floristic elements are correlated negatively with altitude,and the following 3 elements correlated positively with altitude.The proportion of Sino-Himalaya floristic elements increases while Sino-Japan floristic elements decreases as the altitude raises. These two elements are similar in proportion at Alt. 2400m.According to the floristic component and characters of species level,the region can bedivided into 4 sections:<1600m, 1600~2500m, 2500~3600m,>3600m.The belt 1500-1600m is the significative belt in the species level.5.Analysis of the floristic structure, Fr/Fw, Gr/Gw of every aititude zone shows: the climatic attribute of each altitude zone are different from each other.The flora in altitude zone below 1000m shows the attribute of north subtropical zone, the flora in Alt. 1000~2500m shows the attribute similar to warm-central temperate zone, and the attibute of the flora above Alt. 2500m is temperate plateau type.6. Based on analysis of floristic structure and phytogeographical study of concrete taxa, Baishuijiang flora has rooted in the congregation of floristic elements from adjacent regions and local origin.7.According to the verdical distribution of Central China species, Hengduan Mountain species, genera endemic to central China, genera endemic to Hengduan Mountain,the floristic location of Baishuijiang flora is discussed.In the end, proposes for Baishuijiang natural reserve are brought forward,which include verdical layout of the reserve, featural agriculture,plants introduction and breeds cultivate.