| Forest ecosystems play an important role in regulating climate,nourishing water,maintaining soil and water,and preventing wind and sand.However,due to excessive human interference with forests,the original ecosystems in the eroded and degraded areas of southern China have been destroyed and forest vegetation has been lost on a large scale,making revegetation the primary task in the restoration of degraded ecosystems.The ecological restoration process spans successive successional stages,from promoting the recruitment and growth of pioneer populations in degraded ecosystems to re-establishing communities and ecosystems on bare ground.During this process,pioneer populations are in an unstable state with extremely rapid changes in population dynamics and spatial patterns,and studies of pioneer populations during this period can reveal pioneer populations under non-equilibrium conditions and the mechanisms involved in determining successional patterns.In this study,the pioneer species of Pinus massoniana in the erosion zone of southeastern China was used as the research object,and long-term population monitoring fixed sample plots were established.Using the population life history survey data from2011 to 2021 for a total of 11 years and 10 periods,an integral projection model was established,population statistical parameters such as population growth rate and vital rate were output,and the spatial pattern was used to quantify the type of spatial pattern of P.massoniana during the ecological restoration process as well as the spatial pattern was used to quantify the changes in the spatial pattern type and aggregation intensity of P.massoniana during ecological restoration,and the correlation between the population statistics and the aggregation intensity was carried out in the integral projection model.The results of the study show that(1)The survival rate of large individuals of P.massoniana is high(close to 100%),while the survival rate of small individuals gradually decreases as ecological restoration progresses.The average growth of P.massoniana also increases with increasing basal diameter and also becomes higher as ecological restoration progresses.The reproductive rate of P.massoniana shows a pattern of reproduction pushing back as ecological restoration proceeds,with horsetail allocating more resources to growth rather than reproduction.P.massoniana populations showed a pattern of growth(λ > 1)followed by a decline(λ < 1)during this study period,consistent with the pattern of change in population stability.The sixth period is the turning point when the P.massoniana shifts from growth to decline,and when the population is least stable.Elasticity analysis found that the survival of 0-100 mm sized P.massonianas was most important for the increase in population growth rate.Life table response experiments found that when inter-annual differences in population growth rates were small,inter-annual differences in populations remained large,mainly due to the compensatory effect between life rates,where the positive and negative effects of different life rates would cancel each other out.(2)The spatial pattern index analysis showed that P.massoniana showed an aggregated distribution throughout the survey period,but the intensity of aggregation gradually decreased as ecological restoration proceeded.The point pattern analysis showed that in the ecological restoration process,the aggregation of populations at small scales could increase the dominance and form a group effect,which led to the aggregation of P.massoniana populations at small scales.The spatial pattern of P.massoniana populations gradually showed a random distribution as the scale increased due to the uneven distribution of nutrients in the microhabitats within the entire sample site.Spatial correlation analysis showed that the large sized trees and the other life history stages of the P.massoniana population showed no correlation,and the small trees showed a significant positive correlation with newborn seedlings and dead trees,indicating that the population pattern of P.massoniana was mainly restricted by the habitat caused by soil erosion,and the spatial survival response of small sized trees aggregating to increase dominance was adopted.(3)Recruitment(recruitment rate and number of recruitments)of P.massoniana populations was positively correlated with aggregation intensity,and influenced average crowding as an indicator by affecting density.Mortality,on the other hand,is negatively correlated with aggregation intensity and mainly affects the index of agglomeration,which is not related to density.As ecological restoration proceeds,P.massonianas can regenerate in habitats that were previously unsuitable for P.massoniana survival,or where P.massoniana densities are lower,making P.massoniana aggregation less intense.Mortality is mainly due to habitat stress or competition,which is a reflection of the fact that the pine can only survive in some areas,and therefore increased mortality can lead to more aggregation of the population.However,as ecological restoration progresses and regeneration ceases,mortality will become the most important factor controlling the spatial pattern of P.massoniana.(4)As ecological restoration proceeds,the main factor limiting the growth of the population of P.massoniana shifts from stressful habitat conditions to biological factors.Therefore,this study suggests that at the early stage of ecological restoration,emphasis should be placed on seedling conservation;during the period of rapid population growth,it is necessary to ensure benign population growth and selective logging to avoid excessive intraspecific competition;after the ecological restoration reaches a certain level,replanting of native broadleaf species is required to accelerate community succession. |
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