Relationship Between Regenerating Characteristics And Microhabitat Heterogeneity Of Pine-oak Mixed Forests In Qinling Mountains

Pine-oak mixed forest is one of the most typical zonal communities that widely distributed in the Qinling Mountains.Pine-oak mixed forests and mosaic of Pinus tabulaeformis,Quercus aliena var.acuteserrata and Pinus armandii,also called pine-oak belts,are common in the altitude from 800 to 2300 meters in the forest ecosystem of Qinling Mountains.The area of pine-oak belts accounts for more than 40% of total forest area in Qinling Mountains.As the main forest type in the Qinling Mountains,it plays an important role in stabilizing the forest ecosystem of the Qinling Mountains,maintaining biodiversity,and supporting the functions of forest ecosystem services.In this study,we focused on the seedlings and saplings of dominant species and investigated the spatial distribution of pine-oak mixed forest.Semi-variogram analysis and Kriging interpolation were used to analyze the spatial correlation between spatial distribution and 13 environmental factors,including litter thickness,herbal cover,canopy closure,soil temperature,soil moisture content,pH,total nitrogen,total phosphorus,total potassium,available nitrogen,available phosphorus,available potassium,and organic matter,quantitatively.And then illuminate the relationship between regenerating characteristics and microhabitat heterogeneity of pine-oak mixed forest in Qinling Mountains.It would be necessary to understand the significance of microhabitat heterogeneity in regeneration pattern and find the limited environmental factors that affect the seedling establishment of dominant species.This study might provide a theoretical basis in studying community succession of pine-oak mixed forest in Qinling Mountains.The main conclusions are as follows:(1)There are significant differences in the spatial distribution pattern of different growth stages among different dominant species in pine-oak mixed forest.The result of Semi-variogram analysis showed that Pinus tabulaeformis seedlings,saplings,tree structure ratio are over 75%.The structural ratio of saplings of Pinus armandii and sharp-toothed larvae is between 25% and 75%.The structural distribution ratio of the spatial distribution of other life history stages of Pinus armandii and Quercus aliena var.acuteserrata is more than 75%.It showed that the spatial distribution of the three growth stages of the three species is highly spatial autocorrelation.Structural factors strongly influence the spatial heterogeneity.The value of the abutment indicates that the pattern of the three growth stages in different growth stages is consistent,spatial heterogeneity was highest in seedlings,followed by trees,and lowest in young trees.The range value showed that the spatial autocorrelation scales(from 9.5 m to 210.9 m)and the regulations are completely different in different life-history stages for different dominant species.The range of Pinus tabulaeformis is shortest in tree and longest in saplings.The range of Pinus armandii is shortest in saplings and longest in trees.And the range of Quercus aliena var.acuteserrata is shortest in seedlings and longest in trees.(2)13 environmental factors related to settlement and development of seedlings in study area were analyzed.pH,soil temperature and total potassium showed weak variation,and the remaining factors showed moderate variation.There are significant differences among different factors(canopy,herb cover,litter thickness)of different stand.There are significant or insignificant differences in soil physical and chemical properties.The results of semi-variance analysis showed that the spatial distribution ratio of all micro-environmental factors is more than 50%,and most of them exceed 75%.It means structural factors dominate and strongly influence spatial distribution of micro-environmental factors.Canopy closure,herbaceous cover,litter thickness,soil moisture,total nitrogen,total potassium,and available phosphorus showed strong spatial correlation.The model showed higher degree of fitness.The thickness of litter,the coverage of herbaceous layer,and the spatial distribution of available phosphorus have a relatively large range and large spatial autocorrelation scale.(3)The CCA sorting results of trees,saplings,seedlings of 3 dominant species and 13 micro-environmental factors showed that there is a relationship between the spatial distribution of dominant species and the micro-habitat factors.The interpretation rate of 13 micro-habitats to the distribution pattern of dominant species was 35.26%.The distribution of Pinus tabulaeformis seedlings were mainly affected by soil moisture and canopy density.The distribution of Pinus armandii seedlings were mainly affected by organic matter and available phosphorus.Litter thickness and herb layer coverage are key micro-environmental factors in the seedlings distribution of Quercus aliena var.acuteserrata.Seedlings of 3 dominant species affected by different micro-environmental factors.There is a positive correlation between trees and seedlings of Pinus tabulaeformis and Quercus aliena var.acuteserrata,respectively.However,sapling distribution is negatively related to seedling and tree distribution.There is no significant correlation between different stages of Pinus armandi.Different dominant species,spatial distribution of different life stages are affected by various micro-environmental factors.This shows the niche differentiation of the three dominant species and the change of the niche in different stand stage.(4)There are significant correlation between micro-environmental factors and dynamic changes of seedlings of different dominant species.The dynamics of seedling growth and death are affected by complex factors,which vary in different years.The interactions between various factors contribute to the fluctuation of dominant species.Canopy closure,soil temperature,herbaceous cover and litter thickness are main factors that affect the regeneration of pine-oak mixed forests.