Coexistence Mechanisms Of Evergreen And Deciduous Trees Based On Environmental Factors In Tiantong Area, Zhejiang Province, Eastern China

Studies in Tiantong area demonstrate that deciduous component increase in valley area and areas with higher elevations. Preliminary investigation of a20ha plot at Tiantong (East China) showed that while the important value only occupies19.7%of the total important value, the proportion of deciduous trees reached52.6%, and the proportion of deciduous trees in Gutianshan plot which is also in subtropical regions also reached42.8%. How do these evergreen and deciduous trees coexist? Up till now, this question lacks a sufficient answer. Based on the results of background survey in Tiantong20ha dynamic plot and chose evergreen species and deciduous species as objects of study, we started from the distribution character of the two plant groups and their special correlation, and investigate the relationship between topography and vegetation, and analyse the influence of soil nutrient and forest gap to the distribution of tree species so as to preliminarily explore the coexistence mechanism of evergreen and deciduous tree species. The conclusions are as follows:(l)We used pair-correlation function g(r) to analyse special distribution pattern of all the individuals of evergreen and deciduous species with more than20stands.37of the42deciduous species shows aggregation characteristics at the scale of more than20m, among which24species shows aggregation characteristics at all research scale from0-80m;50of the55evergreen species shows aggregation characteristics at the scale of more than20m, among which32species shows aggregation characteristics at all research scale0-80m. Aggregation is the major distribution pattern in Tiantong area.(2)We use cross-pair correlation function g12(r) to investigate the special correlation of evergreen and deciduous species and the results shows that the two plant group only shows positive correlation at small scale (1-7m), and they shows negative correlation at larger scales of more than12m. Due to the first order effects caused by environmental factors, similar habitat preference may lead to positive correlation of two species, and two species may show negative correlation if they prefer distribute in different habitat. So, the results of the analysis may indicate the difference of habitat preference.(3) The results of Torus translation showed that major difference in habitat preferences of evergreen and deciduous trees is in valley and ridge habitats.16.4%of the55evergreen trees and28.6%of the42deciduous trees showed a significantly positive association with the valley habitat, and the proportion of negative association with the valley habitat was40%and7%respectively;41.8%evergreen trees and4.8%deciduous trees showed a significantly positive association with the ridge habitat, and the proportion of negative association with the ridge habitat was10.9%and47.6%respectively. Generally, deciduous species prefer valley habitat and evergreen species prefer ridge habitat. This indicates that habitat partitioning based on topography may be a major mechanism allowing the coexistence of evergreen and deciduous trees in Tiantong area, and that the niche theory, to some extent, may be sufficient in explaining species diversity maintenance in subtropical evergreen forests.(4)The results of univariate variance analysis shows that as the pH value get higher the abundance of evergreen species decrease while the abundance of deciduous tree species increase. Within the same habitat type, abundance of deciduous species increase as the content of C, N and P gets increase. The pH value increase in the following order:ridge, slope and valley. The content of C, N and P is higher in valley habitat than that in ridge habitat. So, the differences in pH value and soil nutrient content maybe the reason for the difference in habitat preference of evergreen and deciduous species. Furthermore, the results of bivariate variance analysis show that the influence of edaphic factors to the two plant group is not based on some single factor but is the interactive consequence.(5)The results of univariate variance analysis shows that in different topography, the abundance of evergreen seedling is higher in non-gap habitat than in gap habitat while the abundance of deciduous seedling is higher in gap habitat than in non-gap habitat. In the same topography, the abundance of evergreen and deciduous species show significant difference in gap habitat and non-gap habitat. The results of bivariate variance analysis demonstrate that gap and gap size can both exert significant influence to the abundance of evergreen and deciduous species. The preliminary research of gap pattern based on topography shows that the ratio of gap area to habitat area, gap density and gap average area are all highest in valley habitat, than in slope habitat and lowest in ridge habitat. This, to a certain extent demonstrates that gap disturbance is an important cause for the difference in habitat preference of evergreen and deciduous species in valley and ridge habitat.