Study On Population Structure And Distribution Characteristics Of Wild Cyatheaceae In Hainan Island

Cyatheaceae are now mainly distributed in pantropical forests.In China Cyatheaceae are all national protected(Class II),mainly found in Yunnan,Guangdong,Guangxi,Hainan,Taiwan,Sichuan,Guizhou,etc.In order to grasp the distribution characteristics and protection status of Cyatheaceae resources in Hainan,this paper conducted a general investigation of wild Cyatheaceae in Hainan Island using spot and sample survey,and recorded 200 spots and 8.64hm2 of sampled area.By applying ecological methodologies of basic population quantitative characteristics such as population density and frequency,age structure analysis using method of spatial sere substituting for time sere,population spatial distribution pattern analysis,static life table and survival curve analysis,for each species of this tree fern family,population characteristics such as population structure,population development and population distribution were generally analyzed and described,upon which the protective effects of natural reserves on population regeneration and recovery were tentatively explored and evaluated.The results showed that:(1)In field survey,five native Cyatheaceae species were found,classified into two genera,including Alsophila latebrosa,Alsophila spinulosa,Alsophila gigantea,Alsophila podophylla and Sphaeropteris brunoniana.Historical recorded Alsophila costularis and Alsophila denticulata were not found.(2)In Hainan Island,Cyatheaceae are widely distributed in all cities and counties except for Haikou City,Wenchang City and Lingao County,mainly found in central and southern mountain area such as Wuzhishan City,Qiongzhong County,Lingshui County,Baisha County,etc.With regard to environmental preferences,Cyatheaceae are mainly distributed in tropical rainforests with a middle and upper elevation range of 400?1000m,a gentle shady slope range,and a middle and higher canopy density range of 40%?80%,forming clusters in moist biotopes such as understory,valleys and riverside,sometimes scattering in shrubs of forest edge.(3)Population densities and population frequencies of five Cyatheaceae are quite different.Based on all data from sample survey,population densities are sorted as follows(from high to low):A.podophylla(194.5/hm2)>A.gigantea(132.2/hm2)>A.latebrosa(122.01hm)>A.spinulosa(88.0/hm2)>S.brunoniana(77.7/hm);population frequencies are sorted as follows(from high to low):A.podophylla(0.63)>S.brunoniana(0.60)>A.gigantea(0.54)>A.latebrosa(0.44)>A.spinulosa(0.38).Compared with outside of natural reserves,overall population density of each species in the natural reserves increases,whereas population frequency remains relatively stable.In general,population density and population frequency are unimodally relevant.(4)Method of variance to mean ratio was used in the analysis of Cyatheaceae population distribution pattern,showing that spatial distribution patterns of five Cyatheaceae populations are all clustered,with aggregating intensity sorting as follows(from strong to weak):A.podophyll?>A.spinulosa>A.latebrosa>A.gigantea>S.brunoniana.For a certain species,aggregating intensity increases from outside of natural reserves to the inside,but showing different degrees of tendency for each species.(5)In natural reserves,populations of all five species are of the growing type,possessing higher proportion of seedlings and young trees and exhibiting higher growth tendency,which indicates that these wild populations have certain potential of natural recovery and regeneration.Human interference might be a negative factor for Cyatheaceae population development.Survival curves of A.latebrosa,A.spinulosa,A.gigantea and S.brunoniana populations are close to Deevey type ?.Survival curve of A.podophylla is close to Deevey type ?.Regeneration of seedlings and young trees is the keystone of population recovery and growth.(6)In typical intermittently consecutive habitat of Cyatheaceae,sample sites were set up,66.6%of which are distributed in national and provincial natural reserves,conserving the majority of wild Cyatheaceae resources.Compared with outside of natural reserves,species diversity and population density of Cyatheaceae have increased in natural reserves,indicating that reducing human interference has certain effect on the protection of speciesdiversity and the recovery of population density of Cyatheaceae.