Study On The Flora Of Vascular Plants And Main Forest Commynities In Yixing

Yixing is located in the southern part of Jiangsu province, lies in the borderline of Jiangsu, Zhejiang and Anhui. There are many low mountains and hills, one of them is Longchi mountain, which is extension of Tianmu mountains; by the impact of the north-sub-tropical southern monsoon climate, heat conditions and precipitation in Yixing area is very abundant; and the yellow-brown soil, made Yixing, which is in the central-subtropical area, being rich in natural resources.The author had a particular investigation about Yixing plant resources in the period from August2009to August2011, collected1982specimens and took2606photos. Based on the the survey results, the paper had a detailed analysis on the basic components of the vascular plants, the characteristics of geographic flora, the relationship with neighboring flora, and major forest communities are also studied. The main results are as follows:There are1436vascular species, be classified into174families,721genera (including low grade species and cultivated species) in Yixing. Among these species, there are97ferns species, belong to25families,51genera;22gymnosperms species, belong to7families,16genera;1317angiosperms species, belong to142families,654genera; among angiosperms,1020dicotyledons speciesm are contained, belong to121families,510genera;297monocots species, belong to21families,144genera. According to the type of vascular plants life-form, there are921herbaceous species,456woody species,59kinds of lianas, the three different types accounted for64.14%,31.75%,4.11%of all vascular plant species.Through the study of geographic flora about the ferns and seed plants, the author learned that Yixing region has a significant subtropical, and transition to the temperate characteristics. Among the ferns, tropical genera accounted for74.29%of all the fern genera; and temperate distribution is occupied25.71%. In the total of215genera of seed plants, the proportion of tropical distribution is40.49%, of which the pan-tropical distribution is mainly tropical ingredients; temperate distribution have303genera, account for57.17%of all the seed plants genera, of which the north temperate is the dominant; so the temperate elements is more advantaged than the tropical emements. In addition, there are13endemic genera, occupied2.45%of all the Yixing seed plants genera, and accounting for5.44%of the total number of endemic genera in China. At the same time, the vascular flora has an ancient character, including some ferns, such as Lycopodium, Selaginella, Equisetum; and lots of gymnosperm, such as Metasequoia, Pseudolarix are age-old genera, other angio sperm, like Magnoliaceae, Hamamelidaceae, Araliaceae, Styracaceae, Sargentodoxaceae are ancient ingredients, too.The trend of species diversity about vascular plants of Yixing showed that the diversity of the tree layer, shrub layer, herbaceous plant was all increased at the low altitude, and get to maximum in the100-150m, then decreased with the rise of the elevation gradient. At the same time, from a life-form perspective, phanerophytes, hemicryptophyte, therophyte were increasing at the low altitude, and then gradually decreasing with altitude rising. The trend of geophytes showed bimodal pattern, the trend of chamaephytes and epiphyte was not obvious due to the small number of species.Through the forest investigation, there are seven types of plant communities in Yixing, involving evergreen broad-leaved forest, mixed forest of evergreen and deciduous broad-leaved, deciduous broad leaved forests, mixed conifer and broadleaved forest, evergreen coniferous forests, bamboo broadleaved mixed forest, sub-tropical bamboo. The zonal plant community type is the evergreen broad-leaved forest. Although some communities belonging to the same kind of community types, but different constructive species show differences in community characteristics. Yixing plant form13kinds communities, consisted of different constructive species. The paper analyzed composition and structure of these forest communities, to provide relevant information to the community diversity and construction of protected zone.