Studies On Population Ecology Of Rare And Endangered Plant Tsuga Chinensis Var. Tchekiangensis In Jiulongshan National Nature Reserve

Tsuga chinensis var.tchekiangensis is a species with a small geographic distribution in the subtropical forests in East China.This species has been listed as Chinese national third protective plant.It has high value concerned its economic and scientific research,but this natural resource is very poor.Up until now,there are few reports of the researches on endangered plant Tsuga chinensis var.tchekiangensis,and mainly focused on the population dynamic,growth characteristics and ectotrophic mycorrhiza.So,it does not give some virtual policy suggestions about the mechanism of species endangerment and conservation strategy of Tsuga chinensis var. tchekiangensis.The aims of our study are to characterize the community structure characteristics,intraspecific and interspecific competition,age structure and dynamics, spatial distribution pattern etc of Tsuga chinensis var.tchekiangensis in different communities,and reveal its endanered condition and endangered reasons,provide some data on species informative for further research on endangered plants Tsuga chinensis var.tchekiangensis.10 plots(20 m×20 m) were investigated along different ridge from low altitude to high altitude in Jiulongshan National Reserve in Zhejiang Province.Using methods of permanent plots and technique of censusing every individual,we indentified and measured all trees in quadrats established in the community to quantify the community structure characteristics.Based on the DBH class frequency distribution patterns,the population age structure of the different tree species were categorized into five regeneration types:Unimodal,Sporadic,Bimodal,Pyramid and Unibar type. According to the biological and ecological characteristics,the population regeneration types of every species were then discussed.At the same time,the diagnosis of succession stage of this community was also carried out,results were obtained.The vegetation and its flora obviously had transitional characteristics and presented the transitional characteristics from tropical area to temperate area.The community was comprised of 24 tree species with 3 co-dominant species:Rhododendron simiarum, Tsuga chinensis var.tchekiangensis and Schima superba.Unimodal type species,such as Toxicodendron succedaneum,Liquidamber formosana,Liriodendron chinense etc., were shade intolerant,pioneer species or long-lived pioneer emergent trees which only regenerated on the bare ground following severe disturbances or in very large canopy gaps.Moreover,these species would disappear finally in the relatively stable community that at later succession stage.Sporadic type species,such as Rhododendron simiarum,Schima superba,Cyclobalanopsis multiervis etc.,were late seral stage species that could regenerate in large gaps and had intermediate shade-tolerance between the pioneer species and dominant species of climax community.Bimodal type species Rhododendron latoucheae was climax community species that had shade-tolerance.Pyramid type species,such as Temstroemia gymnanthe,Eurya muricata,Pieris japonica etc.,and Unibar type species,such as Cinnamomum chekiangense,Camellia cuspidate,Ardisia crenata var.crenata etc., were the dominant species in the upper tree layer and shrub layer of the climax community.Succession stage analysis showed that the Tsuga chinensis var. tchekiangensis community in the Jiulongshan,Zhejiang was still at its early stage,and would develop toward the community climax with the dominant species of Bimodal.The species diversity of tree and shrub layers were analyzed by using Shannon-Wiener index(H'),Simpson index(D),and Pielou evenness index(J_sw). Based on the 2×2 contingency table,interspecific associations of 19 tree populations were studied by different indices:X² test,association co-efficient(AC),percentage co-occurrence.The results indicated that:The tendency of the Shannon-Wiener index, Simpson index and Pielou uniformity index were similar,and the intensity of these indexes for the shrub layer was bigger than that of the tree layer.In tree layer,the species diversity of the upper layer was the biggest.The X² test,together with percentage co-occurrence(PC) and association co-efficient(AC) was effective to measure the interspecific associations.The X² test showed that interspecific association is not significantly correlative in most of the species-pair,the percentage co-occurrence(PC) showed that Tsuga chinensis var.tchekiangensis is positive associated with Rhododendron simiarum,Schima superba,the association co-efficient (AC) showed that Tsuga chinensis var.tchekiangensis is siganificantly negative associated with Temstroemia gymnanthe,Ilex polyneura,Camellia chekiang-oleosa, Cinnamomum chekiangense,Cyclobalanopsis glauc and so on,but Rhododendron simiarum negative associated with Rhododendron latoucheae,Liquidambar formosana,Pieris japonica,Cinnamomum chekiangense,Cyclobalanopsis glauc, Rhus succedanea,Liriodenron,Camellia cuspidata and Pinus taiwanens.Based on a method of increasing the range gradually,the range of intraspecific and interspecific competition in Tsuga chinensis var.tchekiangensis communities were defined.The competition intensity was quantitatively analyzed using Hegyi single tree competition index model.The results showed that:Competition trees range could be effectively determined by the method of increasing the range gradually,and the sample with 7 m radius was the optimum range to study intraspecific and interspecific competition in Tsuga chinensis var.tchekiangensis communities. Relationship between competition intensity and growth of the tree of interest closely followed the following equation:CI = AD^-B.The competition intensity of Tsuga chinensis var.tchekiangensis declined with increasing DBH,and the change was very small when the diameter of the objective tree reached 40 cm.The intensity of intraspecific competition was slightly higher than interspecific competition,which indicated that the survival stress to the Tsuga chinensis var.tchekiangensis population not only came from intraspecific individuals,but also was restricted by other species. Moreover,the main competitions were the dominant species of the zonal vegetation types,including Rhododendron simiarum,Cryptomeria fortunei,Schima superba, Cyclobalanopsis multiervis and Rhododendron latoucheae.The niche over-lap and similarity between the species with broad niche breadths such as Tsuga chinensis var. tchekiangensis and Rhododendron simiarum was greater,which showed that there was great competition between them.Cryptomeria fortunei,a species with smaller niche breadths,but had greater niche over-lap and similarity with Tsuga ehinensis var. tchekiangensis.The main reason was that the competitions on natural resources such as light,soil water and mineral elements while Cryptomeria fortunei and Tsuga chinensis var.tchekiangensis were in young stage.We developed a static life table of Tsuga chinensis var.tchekiangensis population based on the population life table and theory of survival analysis.Survivorship curves, mortality rate,killing power,survival rate,cumulative mortality rate,mortality density and hazard rate were determined,and population dynamics were analyzed using spectral analysis.The results showed that:There were abundant young but fewer old individuals.Population structure fluctuated.The survival curve of the population was Deevey typeâ…¡.Two peaks of mortality rate and killing power existed in the lifespan:the 5th and 15th age class periods.The population survival rate of Tsuga chinensis var.tchekiangensis decreased monotonically,whereas the cumulative mortality rate increased monotonically.Meanwhile,the cumulative mortality rate significantly increased during the 13th age class period,up to 98%.Four survival functional curves showed that the Tsuga chinensis var.tchekiangensis population grew stably at young age,decreased very quickly in middle age and declined in old age.Spectral analysis of the population showed that there was a marked periodic fluctuation in the process of natural regeneration.The spatial distribution pattern and dynamics of Tsuga chinensis var. tchekiangensis population in different habitats,size classes,spatial scale,slopes and altitudes were studied by using six aggregation intensity indexes,such as dispersion index,clumping index,patchiness index,mean crowding index,negative binomial parameter and cassie's index,and two pattern scale analysis methods of Greig-Smith and Kershaw.The results showed that:The distribution pattern of Tsuga chinensis var. tchekiangensis was of the clump in different plant communities,but the intensity was different.In addition,there were some differences among various developmental stages:clump distribution for seedling and saplings,while random distribution for middle and old trees.Different size of blocks had been found to have an effect on the spatial patterns.The figure of pattern scale showed that Tsuga chinensis var. tchekiangensis populations clumped in 8 m² and 32 m² on the whole using Greig-Smith's and Kershaw's mean variance analysis.Tsuga chinensis var. tchekiangensis presented a spatial population distribution whose aggregating intensity raised first and descended later with increased altitude above sea level.Besides,the aggregating intensitie of the populations standing on cloudy slope were higher than those of the populations standing on sunny slopes.The spatial distribution of the Tsuga chinensis var.tchekiangensis populations closely related to their biological and ecological characteristics and habitat conditions,whose evolution also reflected the natural regeneration pattern and process of populations.According to the results as above and some others,the endangered causes of Tsuga chinensis var.tchekiangensis were analyzed.Many factors,such as lower level of seed dispersal,high death rate of seeding and sapling,weaker competition, narrower disturbance range and special adaptive to environment etc have made it very difficult to regenerate,naturally.Finally,some suggeations and strategies were discussed for protecting the endangered plants Tsuga chinensis var.tchekiangensis based on present situation and existing problems.