Population Dynamic Of Pinus Massoniana In Response To Different Understory Vegetation Coverage In Changting Erosion Region

Forests play an important role in maintaining ecological balance and protecting biodiversity,and also provide indispensable natural resources for economic development.Undergrowth vegetation is one of the important components of the forest ecosystem,and it has an important impact on the stability,productivity and nutrient cycle of the forest ecosystem.With the implementation of various ecological restoration measures and vegetation reconstruction projects in the soil and water loss areas in the south,the undergrowth vegetation has gradually developed and continuously changed.The pioneer tree species Pinus massoniana population structure and its dynamics will also undergo continuous changes and adjustments.A field survey in Changting,Fujian found that the Pinus massoniana seedlings were rarely seen in the densely forested areas,which seriously affected the restoration and sustainable development of the Pinus massoniana secondary forest.This article takes the Changting eroded and degraded land as the research area,and takes Masson pine populations that are widely distributed in this area as the research object.Based on the three-year life history survey of Pinus massoniana populations in the low,middle,and high forest cover gradients,an integral projection model（IPM,Integral Projection Model）Combines traditional population statistical analysis methods to reveal the dynamic process of Pinus massoniana population and response strategies for individual survival,growth,and reproduction under different forest vegetation coverage,for ecological management and vegetation restoration of eroded degraded land Provide theoretical guidance.The main findings are as follows:（1）The survival rate of Pinus massoniana in low,medium,and high understory vegetation coverage plots showed significant interannual fluctuations,and there were also significant differences between plots.In the low-forest vegetation coverage plots.With the increase of understory vegetation coverage,the survival rate decreases rapidly as the base diameter increases.When it reaches the stage of vegetation coverage under high forest,there are deaths in all stages of life history.（2）In the stage of low forest vegetation coverage,growth of large individual plants slowed down,growth of medium individual plants accelerated,and overall population growth was low.With the increase of undergrowth vegetation coverage,the population growth increased year by year and was significantly higher than that of low undergrowth vegetation coverage plots,in which the growth of large individual plants was significantly higher than that of small individuals,and the growth difference between individuals gradually increased.（3）Compared with the Pinus massoniana populations covered by vegetation under low forests,the size of horsetail reproduction in the mid-and high-forest vegetation plots appeared earlier.The number of new seedlings continued to decline,and the size difference between individuals gradually increased.The number of new seedlings in the vegetation cover plots in the middle and high forests is mainly limited by the establishment of seedlings,and the Pinus massoniana seedlings in the vegetation cover plots in the low forests are mainly limited by the canopy seed bank.（4）Pinus massoniana populations in the middle and high understory vegetation coverage plots are complete in diameter structure,and the population is in a stable development state(λ_low=0.912,0.903).Among them,the survival and growth of seedlings contribute the most to population development.The positive growth of Pinus massoniana seedlings and small trees can promote the development of the population,and the negative growth and reproduction have almost no effect on the development of the population.（5）In the middle understory vegetation coverage,the population structure of Pinus massoniana population is relatively complete,the population is in a stable development state,and the population growth rate isλ_mid=1.199,1.197.Similar to low-vegetation vegetation coverage plots,the survival of the individual Pinus massoniana is the most important for the population;the growth of the Pinus massoniana seedlings and young trees has a positive effect on the population development,while the positive growth of the large tree hinders the population development;The negative growth of pine is not conducive to population development,while the negative growth of large-diameter grade is conducive to population development;the effect of reproduction on population growth is negligible.（6）In the high understory vegetation coverage plots,the number of seedlings dropped significantly,and the number of trees increased relatively.The population was in a state of decline to expansion and then remained relatively stable.The population growth rate wasλ_high=1.029,1.057.In this plot,the survival of Pinus massoniana is very important for the maintenance of the population.The positive growth of Pinus massoniana seedlings and small trees has a positive effect on the population development.The negative growth of the large diameter level is beneficial to the population development.Reproduction rate has little effect on population growth.