Study On Growth And Natural Regeneration Characteristics Of Platycladus Orientalis Plantation Based On Density

Taking the near-natural Platycladus orientalis plantation in Xujiaya Forest Farm of Feixian County and Daiyue District of Tai ’an as the object,the growth and seed setting law,soil seed bank,regeneration characteristics and population structure characteristics of Platycladus orientalis plantation were studied by investigating the stands with different stand densities,in order to provide theoretical basis and technical support for the near-natural cultivation and sustainable management of Platycladus orientalis plantation in Shandong Province.The main results are as follows:(1)The growth process of tree height,DBH and volume of Platycladus orientalis is affected by stand density and forest competition.The growth curves of Platycladus orientalis with different densities and growth grades are different,and the growth peaks of tree height and DBH are basically staggered.The seed yield of Platycladus orientalis increased with the decrease of stand density,which was closely related to the growth process of trees.The vegetative growth of Platycladus orientalis was inhibited after 6-10 years of fruiting,and the growth rate slowed down.When the fruiting of Platycladus orientalis reached its peak at about 20 years,the annual growth decreased rapidly.The order of seed yield per plant of Platycladus orientalis with different growth grades in the same density was: dominant tree >sub-dominant tree > medium tree > suppressed tree > endangered tree.The seed yield per plant of P.orientalis was affected by the individual growth difference of the plant.The cone yield was significantly positively correlated with the tree height,DBH,crown area and crown volume of the mother tree.(2)The regeneration of Platycladus orientalis plantation under near-natural management showed that there were great differences in the natural regeneration of Platycladus orientalis stands with different densities.The order of regeneration density from large to small was: medium density > high density > low density.With the increase of the age class of the regenerated seedlings,the number of regenerated seedlings showed a downward trend as a whole,which indicated that due to plant competition or external environmental factors,a large number of deaths would occur when the regenerated seedlings of P.orientalis grew to a certain stage,resulting in a gradual decrease in the number with age.The distribution of P.orientalis regeneration seedlings around the mother tree was not uniform,mainly distributed within 7 m from the mother tree.With the increase of the distance between the regeneration seedlings and the mother tree,the density decreased,while the tree height and ground diameter showed an increasing trend,which was consistent with the density dependence theory hypothesis.(3)The growth process of P.orientalis tree height,DBH and volume was affected by stand density.The DBH of Platycladus orientalis analytical trees maintained a rapid growth rate during the period of 0-48 a,and the fast-growing period of medium density Platycladus orientalis was the longest.The intersection point of the average growth and annual growth of DBH and tree height of analytical trees in high-density plots appeared earliest,indicating that excessive high density will limit the full growth of DBH and book height of trees.The dominant trees in the same density stand were in a competitive dominant position,and their tree height,DBH and volume growth were significantly higher than those of other levels of trees,and the advantages were more obvious with the increase of forest age.The annual volume growth of Platycladus orientalis in each dominant grade continued to grow after 50 years,indicating that Platycladus orientalis had a long growth cycle and was suitable for ecological forest.According to the difference of growth law of different density and dominant grade trees,the corresponding thinning period can be determined,so as to improve the effect of near-natural forest management.(4)The average DBH,average tree height and regeneration seedling density of medium density plots were higher than those of high density and low density,and there were large diameter trees.The Platycladus orientalis populations with different densities were dominated by small and medium age classes,and the age structure dynamic index was positive.The population showed a growth structure dynamic relationship at the current stage,among which the medium density population had the highest growth trend,while the high density population had the weakest growth trend,the weakest anti-interference ability and the worst population stability.The highest death peak of middle-low density population appeared in the fourth age class,and only one death peak of high density forest appeared in the third age class.After the next 2,3,4 age classes,the number of individuals in the population is on the rise,but in the long-term development,the high-density and low-density populations may be concentrated in the aging class and the regeneration of the forest is blocked.Therefore,from the perspective of sustainable management,medium-density near-natural management stands are more suitable for the cultivation of Platycladus orientalis plantations.