Light Environment Characteristics Of Pine-Oak Mixed Forest Community In Lingkong Mountain And Its Effect On Seedling Survival

This study was conducted at 400 10 m×10 m quadrats in a 4-hm2 plot of mixed forest dominated by pine(Pinus tabuliformis)and oak(Quercus wutaishanica),which was established in 2011 in the Lingkong Mountain of Shanxi province.The community dynamic characteristics and tree seedling regeneration characteristics were analyzed based on the data of the second survey in 2016.The digital hemisphere photograph(DHP)approach was employed to measure the canopy structure and the understory light parameters.And canonical correlation analysis was used to study the multivariate correlation between them.The survival status of seedlings in 2016 was taken as the research object.The correlation between tree seedling survival and biological factors and light environment was studied from four levels using the generalized linear mixed-effects models(GLMM).The results show that:(1)A total of 5,558 stands of trees of 25 species in 18 genera of 12 families were recorded.In 2016,the number of constructive species varied greatly.Quercus wutaishanica and Pinus tabuliformis died 1 325 and 953 respectively.Compared with 2011,the number of height < 10 m decreased,while the number of height ? 10 m increased.The horizontal structure of plot has not changed.(2)A total of 25,472 seedlings were monitored in 2016,of which 14,425 were new seedlings.In the two surveys,the number of seedlings of the main trees in order: Quercus wutaishanica > Pinus tabuliformis > Acer ginnala > Pyrus betulifolia > Fraxinus chinensis.Compared with 2015,the proportion of number of constructive species seedlings to all seedlings in the plot increased in 2016.(3)The canopy openness(CO)varied from 15.0% to 25.0%,the leaf area index(LAI)from 1.5 to 2.5,and the understory light parameters from 10.0% to 30.0%.It is noted that the dominant species distribution primarily determines the canopy structure and the undergrowth light factors.The canopy structure defines the impact of light factors in the forest,and the LAI is more optimal in describing the canopy's dynamic function.Meanwhile,the CO and LAI index were found negatively correlating to the understory light availability,especially to the abundance of the incident rays of diffused light.(4)Compared with light environment,biological factors had more significant effect on the survival of tree seedlings.And the difference was obvious at each level.At the community level,the seedling survival of all species was restricted by sum of conspecific adult basal area(Acon).At the leaf functional traits level,the seedling survival of broad-leaved species was restricted by Acon.At the habitat level,the survival of the seedlings of the shade-tolerant species is restricted by the conspecific seedlings density and Acon.At the level of species,only the survival of Quercus wutaishanica seedlings was restricted by Acon.