| Forest regeneration is an important means of forest ecosystem self-healing and the basis for maintaining dynamic changes in forest communities.Due to over cutting in the past half century,the quality of natural secondary forest in Greater Xing'an Mountains is low and the status of forest regeneration is poor.The research on forest regeneration in this area plays an important role in improving the stability of dynamic succession of natural secondary forest and promoting the positive succession of secondary forest.This study takes the main forest types in the central part of Greater Xing'an Mountains as the research object,and based on 127 fixed plots in 2017-2019,a comprehensive analysis of the forest regeneration in this area is conducted.The distribution pattern and spatial correlation of seedlings and young trees under different growth stages were analyzed,and the formation mechanism of the spatial distribution pattern of seedlings and young trees was discussed.Seasonal seed rain dynamics,deciduous dynamics,seed rain thousand-grain weight,inter-annual variation of seed rain,and spatial pattern of seed rain of the main tree species in different forest types in this region were analyzed.A global Poisson model and a GWPR model at different scales based on the GWR model were established to simulate the regeneration status of natural secondary forests in the region.The global spatial autocorrelation of the model residuals was described.A small-scale local model was used to evaluate and analyze the forest regeneration status in this area.Finally,this study established a comprehensive evaluation system for the impacts of forest regeneration,and judged the pros and cons of different forest types in the region.The main contents and conclusions of this study are as follows:(1)The amount of seed rain was monitored dynamically for 2 years.The results showed that the larch seed rain and birch seed rain in each forest type showed obvious unimodal distribution.The amount of deciduous leaves of coniferous and broad-skinned species also showed obvious seasonal dynamics,and the deciduous amount of each forest type reached its peak in the middle and early September.In coniferous and broad-leaved mixed forests and coniferous mixed forests,the thousand-grain weight of larch seeds at the peak period is significantly greater than the thousand-grain weight of larch seeds at the initial and final stages.The thousand-grain weight of birch under the three forest types does not show in seasonal dynamic changes There are obvious differences.The seed rain of larch and white birch showed obvious inter-annual changes.2018 is the year of large seed set,and 2019 is the year of small seed set.The spatial pattern of all seed rain was mainly dominated by aggregated distribution.(2)We used the univariate and bivariate O-ring functions of the point pattern analysis method to evaluate the spatial patterns and inter/intra associations of the main tree species in these three forest types at different development stages.The results showed that B.platyphylla and L.gmelinii in birch forest exhibited identical spatial distribution patterns and had a tendency to transition from an aggregated to a random distribution from saplings to adult trees,whereas every tree type in coniferous and broad-leaved mixed forest generally showed a random distribution.Adult trees of the main tree species in coniferous mixed forest,i.e.,L.gmelinii and P.koraiensis,mainly showed a random distribution,but P.koraiensis at other size classes generally showed an aggregated distribution.The intraspecific associations of the main tree species in birch forest and coniferous mixed forest at different development stages were constrained by the spatial scale within a given scope,while those in coniferous and broad-leaved mixed forest at different development stages were not significantly constrained by spatial scale.The results also show that the density of the three forest types was affected by the distance between the individuals of the various tree classes and adult trees,with different levels of influence.Our results further show that the spatial distribution patterns of the tree species in the small-diameter classes were jointly affected by adjacent habitats and diffusional limitations and that scale dependence existed in the intraspecific and interspecific associations,B.platyphylla showed similar associations with L.gmelinii in birch forest,L.gmelinii was not associated with B.platyphylla in coniferous and broad-leaved mixed forest.In the coniferous mixed forest,L.gmelinii(the dominant species)and P.koraiensis were negatively associated at small scales,not associated at intermediate scales,and positively associated at large scales,L.gmelinii mainly showed positive associations with P.sylvestris var.mongolica at all scales,and showed no associations with B.platyphylla.(3)The global Poisson model and the geographic weighted Poisson model(GWPR model)were established to simulate the forest regeneration in the study area.The spatial autocorrelation was analyzed by Moran I statistics,and the effect of scale effect on spatial autocorrelation was explored.The local model under 5km made the best local spatial distribution of model residuals,formed the ideal distribution state of aggregated distribution of different model residuals,the parameter estimates of the model variables produced the largest range of variation,and had the best stability.With the gradual increase of the spatial scale,the stability of the model declined gradually,but still generally better than the global model.Meanwhile,the local model under this scale showed the lowest spatial autocorrelation of model residuals.The number of regeneration trees in the study area is mainly between 1000-2000 trees/hm2,which is higher in the south and lower in the north,and the difference between the East and the west is not obvious.(4)In this paper,19 indexes affecting forest regeneration capacity were selected from five aspects:forest structure,forest factors,soil physical and chemical properties,characteristics of undergrowth vegetation and disturbance.The index weight was obtained by using the method of AHP and entropy weight.The comprehensive evaluation system of forest regeneration influence factors was established,and the comprehensive evaluation value of forest influence factors was obtained by using the linear function comprehensive evaluation method.The comprehensive evaluation value can be used to judge the quality of forest regeneration.The accuracy of the comprehensive evaluation value under different forest types to judge the quality of forest regeneration was more than 90%.Generally speaking,the regeneration of larch forest is better than that of coniferous and broad-leaved mixed forest and birch forest.From the results of the comprehensive study of forest regeneration in this paper,the overall capacity of natural forest regeneration in Greater Xing'an Mountains is at a bad level.In order to ensure the good effect of natural forest regeneration,the way of artificial promotion should be adopted for forest management.In order to improve the status of forest regeneration in this area to the greatest extent,the impact of spatial pattern,spatial relevance,the distance between trees of different diameter classes and the proportion of tree species on forest regeneration should be considered when carrying out the management measures of artificial regeneration(such as tending thinning,artificial replantation,etc.). |
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