Response Of Seedling Regeneration To The Initial Stage Of Close To Natural Forest Management And Promotion Measures Under Different Forest Types

The land forest ecosystem is the main component of the earth’s carbon pool and one of the regional carbon sink capacity indicators.Close to natural forest management measures can accelerate the natural recovery process of secondary forests and plantation forests by defining the target tree,removing disturbing trees,reducing stand density,improving understory microhabitats,and effectively promoting the growth of target trees and natural understory regeneration,which is an important means to improve the carbon sink capacity of forests.However,the species composition,canopy structure,and understory microhabitats of different types of secondary forests and plantation forests are very different,which will cause different responses of different forest types to the seedling regeneration process to close to natural forest management measures.This is crucial for the adjustment of close to natural forest management measures among different forest types to improve their management efficiency.However,there is a lack of research on the response of seedling regeneration processes to close to natural forest management measures in different forest types.This study,typical subtropical evergreen broad-leaved secondary forests and Pinus massoniana were selected in Ningbo,Zhejiang Province（TX-Pinus massoniana+Schima Superba and TX-Pinus massoniana in the TX forest area as well as YW-Pinus massoniana+Scherba and YW-Pinus massoniana+Liquidambar formosana）in the YW forest area were studied By comparing the differences in the natural regeneration process of seedlings and understory microhabitat between the managed（mgt）and unmanaged（CK）plots in the early stage（within 4 years）of close natural management,and the effects of adding different regeneration promotion measures（understory replanting,tilling and weeding）on the effect of close natural management,we used ANOVA and Generalized Linear Mixed models were used to investigate the differences in the response of the understory microenvironment and the natural regeneration process of seedlings to the initial regeneration measures in each forest type,as well as the association between them.Based on this,the cooperative relationship between different regeneration promotion measures and near-natural management measures was also analyzed.The main results and main conclusions of the study are as follows:（1）Leaf area index（LAI）was significantly different among the different forest types,with LAI in the TX-Pinus massoniana being significantly lower than that in the three secondary forest types.The difference between the LAI of the management plots and the control plots within 4 years of close to natural management gradually decreased with the management time,among which the LAI of TX-Pinus massoniana was higher than that of the control plots after 4 years.In addition,the atmospheric and soil temperatures of the two forest types in the YW forest area were significantly higher than those of the two forest types in the TX forest area,but there was no significant difference between the control and management plots.（2）The abundance of germinating seedlings in the management plots of all four forest types was higher than that in the control plots,but only the species richness of germinating seedlings in the management plots of TX-Pinus massoniana+Schima Superba was significantly higher than that in the control plots（P<0.05）.In addition,the abundance of newly germinated seedlings in the management plots was gradually decreasing as the management time increased.In the seedling establishment stage,the seedling establishment rate was significantly higher in all three secondary forest management plots than in the control plots,where only a few seedlings were successfully established into the growth stage in the control plots and only a significant number of seedlings were established in the control plots of Pinus massoniana.However,the growth rate of seedlings after Pinus massoniana establishment was not significantly different between the management and control plots.（3）Under the replanting seedlings,in the TX-Pinus massoniana+Schima Superba,the initial survival rates of Phoebe chekiangensis and Cyclobalanopsis gilva were significantly higher in the management plots than in the control plots,but only the initial growth rates of the sun-loving Cyclobalanopsis gilva were significantly higher in the management plots than in the control plots.In contrast,the survival and growth rate of the initial stage of Cyclobalanopsis gilva and Phoebe chekiangensis within the TXPinus massoniana were higher in the management plots than in the control plots,with only Cyclobalanopsis gilva showing a significant level.Under the tilled and weeded measures,the abundance of emerged seedlings was significantly higher in the management plots than in the untilled and weeded plots in YW-Pinus massoniana+Liquidambar formosana,but there was no significant difference between the two in the control plots.In summary,at the early stage of close natural forest management,its management measures can better improve the light environment in the understory of subtropical broad-leaved evergreen secondary forest and maintain it for a longer period of time,which can promote the germination of natural seeds and the establishment of seedlings in the understory.However,the promotion of natural seedling regeneration by its management measures is limited due to the seed limitation,while replanting seedlings and turning and weeding measures can improve the seed limitation problem and expand the promotion of secondary forest seedling regeneration by close natural management measures through cooperative effects.In Pinus massoniana,the light environment is better in the understory,and the light resources are more abundant in the early stage after close natural management,so it is suitable for replanting species with higher light resource demand to promote seedling regeneration cooperatively.However,the Pinus massoniana has a higher degree of depression in the late stage of management,so the promotion of natural regeneration is limited.If we choose to replant native species with higher shade tolerance,it will help to accelerate the transformation of Pinus massoniana to forests with higher depression.Therefore,for different forest types,we need to apply different regeneration promotion measures to ensure the effective regeneration of the community while increasing forest productivity,and ensure the sustainable growth of forest carbon sink capacity.