The Diversity Of Epiphytic Bryophytes And Its Response To Environment In South Subtropical Urban Forests

With the acceleration of urbanization in the whole world,various threats brought by urban development,such as heat island effects,habitat fragmentation,land-use transformation,instill challenges to the survival of creatures in urban area.How to protect and recover urban biodiversity has drawn more and more attention from people.Epiphytic bryophytes are an important part of forest ecosystem with vital function.But their survival and development are vulnerable to global urbanization due to their sensitivity to environmental changes for their simple structure.We chose a typical south subtropical urban forest Yangtaishan Urban Forest in Shenzhen as our study site,focusing on the diversity,distribution on tree trunk,host specificity,species composition among different stands,environmental factors.We hope that the comprehensive discussion of diversity characteristics and distribution patterns of epiphytic bryophytes in urban forest let us understand their response to the urban environment and provide useful information for epiphytic bryophytes protection and restoration in urban area.According to our survey,38 species of epiphytic bryophytes in 26 genera of 16 families were recorded,including 26 mosses and 12 liverworts.The geographical compositions of plant flora showed that tropical characteristics bryophytes were dominant species in Yangtaishan Urban Forest.Life forms of epiphytic bryophytes was not rich and only 4 forms were found,including 24 species of smooth mat,10 species of turf,3 species of rough mats and 1 species of pendants.Most life forms tended to be drought-tolerant,which reveal that the selection effect of urban environment on the life forms of epiphytic bryophytes.Compared with the surrounding areas,the species richness of epiphytic bryophytes in Yangtaishan area was only lower than that in Tai Mo Shan in Hong Kong and similar to Heishiding in Zhaoqing.And there were the largest number of the same species between Yangtaishan and Heishiding area.Therefore,the diversity of epiphytic bryophytes in Yangtaishan urban forest is not low,but the develop of epiphytic bryophytes may be homogenous.By investigating the species richness and abundance of each bryophyte in each subplot per orientation at each height,we found that epiphytic bryophytes mostly preferred to colonize the north side and the base of the trunks.And there were differences in bryophyte community assemblages among different subplots on the trunk.Among the 16 subplots on the trunk,maximum species richness(31 species)and proportions of total coverage(18.0%)both occurred in the subplot at the base of the trunks(0.3 m above the ground)in the north-facing direction.Jaccard and Bray-curtis similarity index was used to reveal the differences in bryophyte community assemblages among different orientations and heights on the trunk.And we found that there were largest difference in bryophyte community assemblages between the base(0.3m)and the upper(1.8m)subplots of the trunk,as well as the north and the south subplots of the trunk.The number of bryophyte species and coverage of the combined subplots of the south and north of the trunk were 94.7% and 50.1%,respectively.According to the statistics of trees in Yangtaishan Urban Forest,29 species of host trees were investigated,including 20 species of secondary trees and 9 cultivated trees.In the secondary tree,Machilus chekiangensis and Syzygium nervosum had the largest species richness of epiphytic bryophytes(11 species),while in planted tree,Dimocarpus longan and Schima superba had the largest species richness of epiphytic bryophytes(22 species and 17 species respectively).Sematophyllum subhumile and Pylaisiadelpha yokohamae both colonized the largest species number of host trees(17 species)and 16 epiphytic bryophytes species only colonized on 1 species of host trees.The results of Detrended Correspondence Analysis(DCA)showed that there were correlation between some species of epiphytic bryophytes and host trees which may be due to the tree characteristics or environmental factors.To examine the differences of epiphytic bryophytes species richness and abundance between different stands,we used the Kruskal–Wallis nonparametric test and the Mann–Whitney U test,adjusted by the Bonferroni procedure.The results showed that the richness of bryophytes was higher in the urban orchards than in all secondary forests;although the abundance was also higher in the urban orchards than in the secondary forests of the same age.The Shannon index in the orchards was significantly higher than that in either A.pilulifera or C.chinensis forests but not different from that in the other secondary forests.The evenness in the orchards was also significantly higher than that in the C.chinensis forest but did not differ from that in the other secondary forests.Among all the stands,the longan plantations had the highest number of unique species(10 species),and the other stands had few or no unique species.Non-metric multidimensional scaling(NMDS)and analysis of similarity(ANOSIM)methods were applied to examine the differences in the species composition among different stands and there were significant differences in the species composition between the urban orchards and the secondary forests.Canonical Correspondence Analysis(CCA)was used to explain the differences of distribution of epiphytic bryophytes in different stands.The main factors affecting the differences of community composition of epiphytic bryophytes in different stands were microclimate and topographical factors.Based on the correlation relationships between different environmental factors and the species richness and abundance of epiphytic bryophytes,we discussed the factors affecting the colonization of epiphytic bryophytes at sample level in plantations in urban areas.And different counting models were used to model and examine the effects of different environmental factors on the occurrence and growth of epiphytic bryophytes.The results showed that there were 17 species of bryophytes in S.superba plantation.In general,species composition was relatively rich,but some widely distributed species were dominant.At the sample level,environmental factors such as distance from urban built-up area,altitude,microclimate factors,canopy density had a strong correlation with the abundance of epiphytic bryophytes,while the relationship with species richness was weak.Both Hurdle models(HP and HNB)performed well in modeling epiphytic bryophyte colonization and growth.And the key factors affecting the restoration of epiphytic bryophytes in urban plantations are tree characteristics,microclimate and human disturbance.To protect and restore the diversity of epiphytes in urban forests,measures such as cultivating and protecting big trees,promoting canopy closure,controlling human disturbance,and other measures that regulate suitable habitats for epiphytes are needed in the early stages of afforestation efforts.If we wish to restore biodiversity and promote the ecological succession of epiphytes in urban areas,the influence of urban environmental factors on colonization of epiphytic bryophytes should also be considered.