Preliminary Study On Regeneration Mechanism And Influencing Factors Of Platycladus Orientalis Plantation

Artificial forest accounts for 36% of the total forest area in China,which has a very important impact on the overall quality of forest in China.Due to the long-term pursuit of heavy construction and light pipe,the quality of plantation is generally low.Forest regeneration is of great significance to the stability and sustainable development of forest benefits.However,the long natural regeneration cycle,many limiting factors and the lack of management for a long time make the regeneration effect of artificial forest very poor.With the large area of plantation constructed since 1950s entering mature or over mature status,it is necessary to renew the plantation.Platycladus orientalis is one of the pioneer tree species for afforestation in limestone mountain area.In Qingshi mountain area of Shandong Province,the area of P.orientalis is huge and most of it is artificial forest.The investigation of P.orientalis foreston the opposite side shows that the regeneration under the forest is uneven.The seed germination and seedling establishment stage of regeneration process are very sensitive to the external environment.In this paper,the P.Orientalis plantation in hongdingshan of Dongping County,Tai'an City was taken as the research object.Through field and pot experiments,the seed germination and seedling establishment in the process of understory regeneration of P.orientalis plantation were studied deeply and systematically,in order to find out the key limiting factors and regeneration rules,and to provide effective artificial promotion technology.The results are as follows:(1)Stand density has a certain effect on soil physical and chemical properties.The soil pH value,total salt content and total phosphorus content of low-density stand were significantly higher than those of middle and high-density stand,but the differences of total nitrogen,hydrolytic nitrogen,available phosphorus,available potassium and organic matter were not significant.The difference of soil water content between different density stands is significant,and the difference between months is extremely significant.The lowest water content of low density stands is significantly affected by rainfall and temperature.(2)The density of soil seed bank reached the maximum in September when the seeds were mature,and the density of soil seed bank in high-density stands was the maximum;the seed vigor gradually decreased with the extension of time after maturity,and it was the lowest before the seeds were mature in that year.(3)The growth of regeneration seedlings was significantly different under different stand densities.With the increase of stand density,seedling height and ground diameter of seed lings gradually decreased,root length,root surface area,root volume and root average diameter gradually decreased,root biomass ratio increased first and then decreased,stem biomass ratio decreased,and leaf biomass ratio increased.The seedlings of over dense regeneration are short,the roots are underdeveloped,and the proportion of leaf biomass is increased.In the forest,the number of young seedlings that germinated in the same year decreased obviously,and the retention rate was very low.(4)Biological factors such as the age of mother tree and the size of seed have significant effects on Seed Germination and early growth of seedlings.With the increase of the age of the parent tree,the germination rate and germination index of the seeds increased,but the biomass of the seedlings after germination decreased significantly except the stem biomass.In terms of seed size,large seeds have higher germination rate,germination index,vigor index and average germination time than small seeds.The root,stem,leaf biomass and total biomass of large seeds are larger than those of small seeds,which is more obvious under adversity.(5)Environmental factors such as soil water content and litter thickness have significant effects on Seed Germination and early seedling growth.With the increase of PEG concentration,the germination rate(GR),germination index(GI)and vigor index(VI)decreased significantly,and the average germination time(MGT)increased significantly,When the PEG concentration reached 20%,the germination rate was 0,and the length of embryo(GL),radicle(RAL),embryo/radicle,root length(RL),root surface area(RSA)and root volume(RV)decreased significantly with the increase of PEG concentration.With the increase of litter thickness,the germination rate,average germination time,germination index and seedling height of P.orientalis seeds increased first and then decreased,the ground diameter increased in waves,the root,stem,leaf biomass and total biomass increased first and then decreased,the root biomass ratio and root crown ratio of seedlings increased in waves.It showed the best germination and seedling growth effect at 2cm.Through the study,the following suggestions are put forward:appropriate cutting and maintaining the appropriate stand density are the key measures to ensure the regeneration of the forest,and the density is appropriate to maintain about 1300 plants/hm~2;the places with low seed bank density and poor regeneration of the forest can be updated through timely Artificial Supplementary sowing;reasonable regulation of litter thickness can effectively promote the regeneration of the forest,and the litter thickness is appropriate to 2cm.