| Michelia shiluensis et Y.F.Wu,belonging to family Magnolia,is one of the endemic plants and national class II endangered protected species in Hainan Island.It had a sporadic distribution in mountainous areas in the south and central of Hainan I sand,including Baisha,Changjiang,Wuzhishan and Lingshui,which had very important scientific research and protection value.Due to the predatory exploitation and theft by illegal traders,wildlife resources are further lost,and natural survival and reproduction are seriously threatened,even endangered.In this study,Michelia shiluensis was taken as the research object.Based on the comprehensive field investigation,reproductive ecology,population and community structure were carried out in Diaoluoshan Nature Reserve to study the causes of endangerment of the species.The main results were as follows:(1)The investigation of the distribution areas of Yingge,Nangaoling,Baomeiling,Wuzhishan and Diaoluo Mountains has all been disturbed to varying degrees,especially in Baomeiling and Diaoluo Mountains.In addition,a large-scale mining of iron ore and limestone in Shilu Town near Baomeiling has caused serious damage to the local natural vegetation,resulting in Michelia shiluensis hardly found and collected in the collection site of its model specimens in recent years.Four populations,Naoge Ridge,Nankaolin,Baomeiling and Wuzhishan,are seriously short of Smiling Individuals in Shilu,especially in young ones,and also show incomplete age structure.The population resources in the Diaoluo Mountains are abundant,and the natural regeneration and growth and development are relatively good.(2)There are 247 species of vascular plants in Michelia shiluensis community,158 genera and 77 families.Among them,few families account for 57.14%of the total families,single families account for 38.96%,medium families account for 3.9%,and there are no larger families or large families.There are 119 genera,accounting for 86.23%of the total genera.Tropical elements are dominant in the distribution areas of families and genera.Among the distribution types of families,there are 43 families of tropical components,accounting for 82.72%of the total families.Among them,the tropical widespread family is the largest one,with a total of 25 families,accounting for 48.16%of the total number of families.Among the floristic components of families and genera of seed plants in Michelia shiluensis community,tropical components are dominant and absolutely dominant.Tropical distribution is dominant at all levels.The dominant distribution types of families and genera at all levels of the community were the same as those of the community.There are 119 genera in the tropics,accounting for 86.23%of the total genera and 43 families,accounting for 82.72%of the total families.In all levels of Michelia shiluensis community,the species diversity index showed the same results:shrub layer>tree layer>herb layer.In conclusion,the order of stability at all levels of the community was from high to low:shrub layer>tree layer>herb layer.(3)The results of x2 test showed that there were more positive correlations between Michelia shiluensis population and shrub layer than tree layer,and more negative correlations between tree layer and shrub layer.The number of related species was the same,and the results of 2 test could be regarded as the same.The results of Pearson correlation coefficient test and spearman rank correlation coefficient test were consistent.On the whole,Michelia shiluensis was related to most plant populations.There was no significant interspecific association,the interspecific relationship showed a general loose trend,the trend of population independence was obvious,the degree of randomness was large,and the association between species and Michelia shiluensis in the community was loose.Tree and shrub layers were positively correlated with this plant in general.The number of species is more than the number of negatively related species,and the development of community tends to be beneficial to Michelia shiluensis.(4)The age structure and survival curve of Michelia shiluensis population showed that Michelia shiluensis population showed a increasing trend.From the age structure of the population,it is inferred that there is a high mortality rate between the first age class and the second age class,and between the fifth age class and the sixth age class.The population of Michelia shiluensis was clustered.Aggregation intensity is the highest at 25 m2,and it should be noted that at the scale of 200 m2,the aggregation intensity reaches the maximum again.On the scale of 25 m2,the aggregation distribution of Michelia shiluensis population is related to its own biological characteristics,which mainly results from its own biological characteristics,On the scale of 200 m2,the spatial heterogeneity of the environment leads to the maximum aggregation intensity.Because Michelia shiluensis is mostly born in valley and hillside areas with better forest gaps,its habitats are very different,which results in patch aggregation on a large scale of pattern.The distribution pattern of Michelia shiluensis population changes from saplings to small trees to adult trees to big trees:aggregation to uniformity.In young trees,because of its biological characteristics,Michelia shiluensis mainly presents aggregation distribution.In mature trees,the population distribution pattern begins to shift to uniform distribution,and in the big tree stage,the population distribution pattern has been completely uniform distribution.On the small scale(25 m2 and50 m2),the distribution pattern changes from saplings to saplings were consistent with those from saplings to adults.(5)The main reasons for the endangerment of Michelia shiluensis are as follows:single pollinator,low pollination efficiency and short flowering period;most seedlings could not pass environmental screening,resulting in higher mortality rate;particularity of environmental climate and habitat requirements;human disturbance,and exploitation of wild resources. |
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