Natural Regeneration Characteristics And Seedling Response To Nitrogen Addition Of Constructive Species In Pine Oak Forest Community On The Western Of Qinling Mountains,China

The main constructive species of natural secondary forests in the Qinling Mountains are Quercus aliena var.acuteserrata,Pinus armandii and Pinus tabuliformis.The pine forest,oak forest and pine-oak mixed forest formed by them are widely distributed community types in the Qinling forest area,and are vital in maintaining the stability,biodiversity and ecological service functions in the forest ecosystem.Regeneration ability of the constructive species in the forest community directly affects the stability and service function of the forest ecosystem.However,there are several questions that need be answered: 1)Whether the main ecological factors affecting the regeneration of constructive seedlings in pine oak forest community with dynamic succession relationship are consistent? which stage restricts the transformation of constructive species seedlings to young trees? and the ecological factors affecting the transformation process Is it consistent? The answers to those questions are vital for revealing the natural regeneration pattern.This study took three natural secondary pine oak forest communities on the western of Qinling Mountains as the research objects,and set up four replicated quadrats for field investigation.Initially,we investigated the species composition of constructive species,then the diameter class structure,spatial distribution pattern,regeneration characteristics of seedlings and saplings were analyzed.Secondly,the effects of 10 environmental factors,such as light index(LI),soil moisture content(SMC),total phosphorus(TP),etc.on the regeneration and survival of constructive species seedlings,were determined and analyzed.Finally,through field potted control experiments,the survival response of constructive species seedlings with different ages to nitrogen addition in the external environment was explored.The research is vital for revealing the natural regeneration characteristics of the natural secondary pine oak forest community,clarifying the main ecological factors affecting regeneration,inferring the succession trend of the community and promoting restoration management.The study reached the following main conclusions:(1)The population diameter level structure of the three natural secondary pine oak forest communities was similar to the inverted J type,which was a growing population but there were differences in the regeneration characteristics.In the pine forest and pine-oak mixed forest,the regeneration of Pinus armandii is best,and in the oak forest,the regeneration of Quercus aliena var.acuteserrata is best.The spatial distribution pattern of constructive species changed from aggregation distribution to random distribution with the increase of scale,the spatial distribution pattern of Quercus aliena var.acuteserrata was affected by habitat heterogeneity,and the spatial distribution pattern of Pinus tabuliformis and Pinus armandii were affected by the restriction effect of homogeneous density.(2)There were significant differences but consistencies among the 10 environmental factors in the three natural secondary pine oak forest communities.In addition to soil available phosphorus(SAP)and ammonium nitrogen(AN),other environmental factors differed significantly in the three natural secondary pine oak forests,and the spatial autocorrelation of environmental factors in the pine-oak mixed forest was lower than in the pine forest and oak forest.(3)The main ecological factors affecting the renewal and survival of constructive species seedlings in the three natural secondary pine oak forests are different.In the pine forest,it is the soil total phosphorus(TP),which mainly affects the renewal of the Pinus tabuliformis;in the pine-oak mixed forest,the soil moisture content(SMC)is mainly affected the survival of the Pinus tabuliformis;in the oak forest,it is the light index(LI),which mainly affects the renewal and survival of the seedlings of Pinus armandii and Quercus aliena var.acuteserrata.(4)The effect of nitrogen addition on the survival rate of constructive species seedlings of different seedling ages under three natural pine oak secondary forests was inconsistent.Nitrogen addition improved the survival rate of Quercus aliena var.acuteserrata,especially4-year seedlings under oak forest.Nitrogen additions had no significant effect on the survival rate of Pinus tabuliformis and Pinus armandii.