Analyses on community characteristics and its relict and conservation of Cathaya argyrophylla at Bamianshan in Hu'nan Province

In order to understand current survival status of Chinese endemic relic plant Cathaya argyrophylla Chun et Kuang, C. argyrophylla+Tsuga chinensis var. tchekiangensis ( Flous) Cheng et L.K. Fu+Castanopsis eyrei ( Champ.) Tutch.-Rhododendron simiarum Hance community located at Jiaopenliao of Bamianshan in Hu’nan Province was investigated, its community characteristics and population age structure were analyzed, and generic areal-type and its similarity coefficient of spermatophytes in six communities distributing in different regions were compared. On this basis, relic characteristics of C. argyrophylla community was discussed. The results show that there are 66 species of vascular plants in C. argyrophylla community at Jiaopenliao, including 4 species of ferns and 62 species of spermatophytes (4 species of gymnosperm, 58 species of angiosperm) . Main dominant species in arbor layer of the community are C. eyrei, R. simiarum, C. argyrophylla and T. chinensis var. tchekiangensis, with important values of 13. 12%, 9. 28%, 8. 86% and 7. 49%, respectively. Simpson and Shannon-Wiener diversity indexes of the community are 0. 94 and 3. 20, respectively, and Pielou evenness index Jsw and Jsi are 0. 81 and 0. 92, respectively. It means that species diversity of the community is lower, but species distributes well, and its characteristics is consistent with that of warm coniferous and broad-leaved mixed forest in mid-subtropical mountainous region. Based on life-form spectrum, percentage of frequency in the community from high to low in sequence is A class, B class, C class, D class, E class, which is consistent with Raunkiaer’ s standard frequency diagram, it means that the community is totally in relatively stable subclimax state. Based on age structure of C. argyrophylla population, middle and young age individuals in population occupy a certain ratio, while ratio of middle age individuals with 80-180 a is lower. Based on diameter-class structure of dominant species in the community, C. eyrei, R. simiarum and Rhododendron latoucheae Franch. populations are belonged to growing type, while C. argyrophylla, T. chinensis var. tchekiangensis and Fokienia hodginsii ( Dunn ) Henry et Thomas populations are belonged to declining type. Based on generic areal-type of spermatophytes in C. argyrophylla community at Jiaopenliao, temperate areal-type genera account for 51. 06%, which is slightly higher than tropic areal-type genera ( accounting for 48 . 94%) , meaning that this region is located in the transition area of tropical and subtropical. Besides latitude, altitude also has a certain effect on areal-type elements. In six C. argyrophylla communities located in three floristic subregions of North Guangdong, Guangdong and Guangxi mountainous region and Guizhou Plateau, similarity coefficient of generic areal-type of spermatophytes is 0 . 35-0 . 67 , the genera containing constructive species in community have similarity and intercommunity among different communities, such as Tsuga ( Endlicher) Carriere, Machilus Nees, Fagus Linn. and Fokienia Henry et Thomas, etc., and most of them are relic and conservative elements, indicating that existing communities of C. argyrophylla have similar vicissitude history, the distribution area has obvious characteristics of subtropical mountain shelter, showing relict and conservation of its succession process. It is suggested that moderately exploring forest gap in C. argyrophylla community and decreasing canopy density in forest understory will be beneficial to growth of young tree and keeping C. argyrophylla population continuous renewal and succession.