Comparative Study Of Mid-Montane Humit Evergreen Broadleaved Forests Between Southern Part And Northern Part Of West Slope In Gaoligong Mountain And Corridor Effect To Flora Distribution In Gaoligong Mountain

Characterized by longitudinal mountain ranges and deep valleys, Gaoligong Mountain is an import part of the longitudinal range-gorge region (LRGR) in southwest China, and is possessed of distinct"corridor-barrier"phenomenon. Both located in Gaoligong Mountain, west slope of the northern part located 2 degree north to west slope of the southern part, 200㎞ away form west slope of the southern part. Mid-montane humit evergreen broadleaved forests (MHBF) of two regions are the largest and best reserved mainly type of vegetation. In west slope of the northern the forests occupies a mountainous region scope with altitude of 2300~2700m and in west slope of the southern part it distributes between 2300～2800m. The distributed altitude of MHBF in the two regions is closed.According to Information of the twelve samples (total area of 6000 m2)in west slope of the southern and northern parts in Gaoligong Mountain, comparative study species composition, floristic character, community character, species diversity and life form of MHBF in west slope of the southern and northern parts, and discuss the embodiment of the corridor function between two regions of MHBF. The results show that:(1)The plants of MHBF in two regions are rich all, although there were more abundant vascular plants in MHBF in west slope of the northern part than in southern part. There are a total of 79 families, 134 genera and 259 species in west slope of the northern part; at that time, there are a total of 76 families, 126 genera and 212 species in west slope of the southern part. There were more abundant fern in MHBF in west slope of the northern part than in southern part. Composition of major familes and gunera in two regions are very similar. But the southern part of GLGM had higher degree of differentiation in family and genus level, which was resulted from the abundant precipitation, wetness advantageous in northern part.(2)The floristic analysis showed that the floristic characteristic of seed plants families in both regions were tropic and the tropic characteristic in west slope of northern part was a litter lower than that of west slope of southern part. In genus level, the temperate characteristic in west slope of northern part was a litter higher than that of west slope of southern part due to its higher north degree. Both regions had transitional characteristic from tropic to temperate. In species level, both regions have distinct temperate characteristic, and is greatly affected by tropic characteristic. The flora of the west slope of northern part showed close relationship with Himalaya area. Both regions have similar origin and weak relationship of seed plants floristic. The flora coefficient of similarity of two regions is descending in family, genus and species levels that were separately 64.9%, 37.5% and 11.3%. Endemism in west slope of the northern part is more notable than west slope of the southern part's. The proportion of endemic to China species in west slope of the northern part was lower than that of west slope of the southern part. But this area contained more species endemic to Gaoligong Moutains. It is showed higher endemic extent about habitat in west slope of the northern.(3)There were big different formations types between two regions of MHBF. In west slope of the northern part, MHBF's dominant species were Cyclobalanopsis lamellose and Symplocos dryophila. In west slope of the southern part, MHBF's dominant species were Lithocarpus hancei and Lithocarpus variolosus. It suggested that both regions differences is result from north degree's affections under the similar altitude conditions (2200~2800m). It suggested that discrepancy of energy and subdivided precipitation what result from Geographical link and region of Latitude is affected on formations and species.(4)Both regions, the sort of vascular plants'frequency isⅠ﹥Ⅱ﹥Ⅲ﹥Ⅳ﹥Ⅴ.The number of species what have lower frequency are more than that have higher frequency. It showed that community of two regions have similar characteristic of plant distribution and composed frame. The comparison of species composition indicated that the dominant families and genera were similar between two regions's tree, shrub, hurb layers; thouth the species abundance in west slope of the northern part was higher than west slope of the southern part. In community structure, the most different aspect between two regions was the distribution of bamboo. Fern is occupied the dominant position in hurb layer in both regions, according with the characteristic that MBHF have fern layer.(5)There were big similar diversity index(Simpson index,Shannon-Winener index,Pielou index) between two regions in tree,shrub,hurb layers, except the species abundant index in west slope of the northern part'hurb big than that in west slope of the southern part'hurb.It adequately showed the function of corridor phenomenon that advanced forming species diversity (6) There were big similar about life form spectrum, leaf scale spectrum, characters of leaf between two regions. Phanerophytes occupied the dominant position in life forms in both regions. In west slope of the northern part the rate was higher, which was corresponding to its humid condition. In both regions, Mesophyll leaf is occupied the dominant position. Mesophyll leaf occupied the proportion in west slope of the northern part is higher than that in west slope of the southern part, with its herb layer rich in ferns on the west slope of the northern part of the abundant rainfall, humid habitat as community characteristics closely related. In both regions, giveing priority to simple leaf, paper leaf, non- edge leaf, acumination leaf about the leaf character, which was corresponding to MHBF character.(7) There is a similarity of MHBF between these two regions in community structure, richness of families and genera composition, existence, diversity and life form which shows the"corridor"phenomenon of flora distribution which caused by cordillera in long direction vally. There are 30 species in total, in these two regions, in which some are moving and communicating in the direction of north-south orientation. The formation and changes of the distribution range both showed the effect of the corridor. In the same species level, the diversity level of west slope noth part is higher than the north part. The composition of flora division of western slope northern section is close to Himalaya area. The main differences between these two sections are: the northern section is very humid and abounds in rain, has relatively low heat and connect to Himalaya area. It indicates that geographical Corridor effect is more apparent and evident than latitudinal humidity-heat effect.