Populationdynamics Analysis Of Pinus Massoniana Ongranite Eroded Landin Changting County

It is an important way to effectively guide ecological restoration and practice to identify the change of population characteristics and influencing factors of key species in degraded ecosystem.As a native tree species and pioneer tree species for ecological restoration and reconstruction of the red soil erosion region in south China.Pinus massoniana becomes the main part of vegetation in the preliminary control area of soil and water loss.In the granite poor land with serious soil erosion,Pinus massoniana which has been banned for many years is restricted by the habitat stress brought by repeated soil erosion,and often forms the degenerating Pinus massoniana.As the key premise for the follow-up control of soil and water loss,it is necessary to clarify the quantity,structure,survival and development status of the population of Pinus massoniana in the eroded land through the study of population dynamics.The population of Pinus massoniana in the granite eroded poor land in preliminary control area for soil erosion in Changting was studied in this paper.We use the methods of spatial substitution time series which including static life table,survival analysis function,time-sequence forecasting model,and the theoretical model method including integral projection model(IPM)respectively.The age structure and life history characteristics of the whole population of Pinus massoniana were analyzed.Besides,the characteristics of individual survival,growth and reproduction of Pinus massoniana in the process of natural recovery,as well as the changes of the transient population dynamic and the response mechanism to habitat stress of eroded poor land were analyzed.The results are as follows:(1)In the age structure of Pinus massoniana population,the number of individuals in the young stage is abundant with a low renewal survival rate of deposit;the number of adult individuals is small and the growth rate of the property was slow.The survival conditions of young and adult ages were not stable,and the death density of the population was high in the middle of adult ages and young ages.Death occurred at all ages,and the population survival curve belong to Deevey-? type,which was in dynamic stability.The time-sequence model demonstrates that the number of adult individuals would increase.(2)With the change of recovery time,the individual survival risk of seedlings(0 <basal diameter ?5 mm)in each period is always the highest.The survival of saplings(5mm < basal diameter ?25 mm)is relatively fragile,and the consumption of habitat resources will reduce the survival probability of middle-aged individuals gradually.The average individual growth of Pinus massoniana in different periods has little difference,but the "negative growth" is obvious,which reflect the limited growth of biomass of degraded Pinus massoniana.The average annual growth of individuals in the middle of adult age(50mm < basal diameter? 75mm)is the lowest among all adult individuals,which is corresponding to the results of survival analysis function.The reproductive status of individuals and the difference of individual reproduction interannually are all related to the reproductive distribution of individuals.The difference in the number of new seedlings produced by a single pinecone reflects the limitation of the combined effect of habitat stress factors on the stage from seed germination to seedling.(3)The IPM model output results show that the contribution to survival of seedlings and young trees and reproduction of adult individuals are extremely low;maintenance is more and more dependent on the negative growth of population of adult individuals;as the recovery time longer,population can't get the supplement of the young trees,and the individuals of largest contribution to the growth of the population transform from the middle of adult individual to mature individuals,bringing the adverse consequence of obvious growth restriction shrinkage.Mature individuals will be replaced by adult individuals,which means the number of mature individuals will increase,turning into slow-growing degenerating Pinus massoniana forest,and the whole population will decline in the future due to the lack of sapling supplement.(4)Both the spatial substitution time series method and the IPM model analysis showed that the survival of seedlings and saplings and the middle of the adult stage are the vulnerable links in the development of the population,which then affect the stable development of the population.However,the spatial-temporal method assumes that the experienced environmental conditions remain unchanged,and it is limited to infer the temporal dynamics of the population based on the number of surviving individuals in a certain time section.The IPM model incorporates the survival,growth and reproduction status of individuals per unit time,and the output results are more accurate and richer incontent.