Response Of Pinus Massoniana Population Dynamics To Short-term Climate Fluctuation In Changting Soil Erosion Area

The IPCC report indicates that the frequency and intensity of extreme weather events such as droughts,floods and heat waves will increase in the future,and the frequency of changes in temperature and precipitation are likely to increase accordingly,which are increasingly becoming key factors driving changes in forest ecosystems.Most previous studies have focused on the effects of climate fluctuations on individual tree physiology,describing the relationship through analysis of plant physiological indicators.When looking at the population scale,it has been found that the effects of climate fluctuations on individual physiology can lead to varying degrees of change in population life history parameters such as survival,growth,and reproduction.In the case of population dynamics,any factor that affects population dynamics must act by influencing population life history parameters,which in turn may affect species coexistence and even the stability of the entire ecosystem.Methods for the study of population dynamics continue to innovate from static life tables to matrix models to Integral Projection Models(IPM).As climate fluctuations increase,it is essential to consider climate variables and population dynamics together.In this paper,the Standardized Precipitation Evapotranspiration Index(SPEI)at annual and seasonal scales is calculated by using the basic meteorological data obtained from the China Meteorological Data Network for 2011-2020.The population dynamics was studied in the erosion zone of Changting County,Fujian Province,by measuring the population survey data of P.massoniana in the same period as the meteorological data.A new IPM was constructed by incorporating SPEI into the vital rate function with the help of General Linear Mixed Model(GLMM),analyzing the climate fluctuation pattern in the erosion zone of Changting,exploring the vital rate changes of P.massoniana under the influence of short-term climate fluctuation,and elucidating the population dynamics of P.massoniana and the adjustment mechanism of its life history strategy,with the aim of providing a basis for the ecological restoration of the erosion zone of Changting.This study aims to provide theoretical guidance for the ecological restoration of Changting soil erosion area.The results of the study showed that:(1)The frequency of annual droughts in the Changting erosion zone is relatively low.However,precipitation is low and temperatures are high in summer and autumn,and high temperatures are not fully synchronized with heavy rainfall.The frequency of typhoon landings affects the amount of precipitation,resulting in sharp short-term climate fluctuations in the area and frequent seasonal droughts from July to September.(2)The effects of short-term climatic fluctuations on populations will be reflected by changes in vital rates.For the population survival of P.massoniana,it was more obviously affected by climate fluctuations and concentrated in the second and third seasons.When the climate is drier,the population survival decreases significantly,especially for the smallsized of P.massoniana.For the growth of the P.massoniana population,even though the growth variation of long-lived species was relatively small,the results showed that shortterm climatic fluctuations during the growing season still had an impact on the trees.Growth increases were more pronounced when the climate was drier.When the climate was relatively wet,growth increased in large-sized P.massoniana and decreased in small-sized.The lack of synchronization between climate fluctuations and tree growth changes reflects a certain lag in the effect of climate on tree growth.The effects of short-term climate fluctuations are more complex for the reproduction of the P.massoniana population.Reproduction of large-sized P.massoniana was positively correlated with SPEI to some extent,while the opposite was true for small-sized.Small-sized of P.massoniana populations produce early reproduction when they are significantly stressed by climatic fluctuations.(3)In the Changting erosion zone under the influence of short-term climate fluctuations,P.massoniana populations showed an obvious trend of decline(λ<1),and the main influence on population growth was population survival.Under the influence of shortterm climate fluctuations,the reproduction of large-sized P.massoniana was relatively little affected,while small-sized were severely affected and the population structure was extremely unstable.Under the influence of climate fluctuations,there is a certain variation among the population vital rates,and when the death of the P.massoniana population increases,individuals will experience an increase in growth or advancement of reproductive diameter class,etc.,to resist the negative effects of climate fluctuations on the population and thus maintain community succession.