| Pinus armandii is an arbor species endemic to China.It is of great significance in theory and practice to study the population dynamics and stand growth of P.armandii.In this paper,the population of P.armandii in Qinling Mountains was investigated and analyzed,and the static growth table of P.armandii was drawn to understand its growth status.Combined with surface soil pollen analysis and vegetation composition,the distribution shift of P.armandii population in Qinling Mountains was verified.The physicochemical properties of soil were analyzed.The variations of soil nutrient content and elements in the P.armandii forests were tracked.The relationship between the diversity of P.armandii forests and soil conditions was explored.Based on the existing biomass model,re-fitting the empirical equation of biomass of P.armandii,and then introducing the tree growth model Moses to simulate the growth of P.armandii stand in Qinling Mountains and finally to evaluate the carbon sink capacity of P.armandii forests in Qinling Mountains.The main findings are as follows:(1)We found that the P.armandii forests comprised two main forest types.One was the same-generation and single-layer heterogeneous forest,mostly coming from the remained maternal recovery of the forests in China in the 1960 s.The other was the multi-generational stratification heterogeneous forest,renewing based on the former forest,after the implementation of natural forest protection project in China.The diameter at breast height and height class structures of P.armandii reflected the composition of these two forest structures of P.armandii to some extent,with their own bimodal structures.According to the death curve,survival curve and static life table,the growth and survival trends of P.armandii population at middle and low age classes were relatively stable,while the P.armandii population at older age class had a higher mortality rate.(2)Based on the relationship between vegetation composition and surface soil pollen analysing,we confirmed that the geographical distribution of P.armandii population gradually changed in Qinling Mountains.Combining the current situation of the lower limit of the upper limit of the forest edge in the existing observations,and the experimental results of the disappearance of P.armandii in the blank plot with relatively low elevation,we speculate that the geographical distribution of the P.armandii in Qinling Mountainsis moving towards high altitude area,and the distribution range is gradually narrowing.Increasing temperatures will continue affecting the distribution shift of P.armandii,and the P.armandii population will exhibit ecological adaptability to habitats with higher altitudes or norther latitudes.(3)The soil physical and chemical properties of P.armandii forests in Qinling Mountains have obvious spatial heterogeneity,and the differences are mainly concentrated in soil layer A.The soil physical properties of P.armandii forests in Qinling Mountains change with the change of soil layer,and they have significant differences in the forests with different dominating species Generally,the species diversity in the P.armandii forests clustered with two the true Shannon Index of 1.98 and 3.86 has a significant impact on the soil physical and chemical properties,and the physical and chemical properties of P.armandii forest in Qinling Mountains are closely related to the species diversity.Soil fertility of mixed forest is higher than that of pure forests while soil physical properties are not affected by stand composition.The species diversity will affect the physical and chemical properties of soil under the forest,especially the physical and chemical properties of soil layer A.(4)The soil nutrient content of P.armandii forest in Qinling Mountains is accelerating degradation with time.The soil nutrient elements of P.armandii forest,especially the available nitrogen and phosphorus content decreased significantly in the area.The soil organic matter content and the total nitrogen and total phosphorus content also existed different degrees of decline.The ever-increasing annual average temperature gradually become the highest explanatory factor for the change of soil available nitrogen content in P.armandii forest in Qinling Mountains,and the soil available nitrogen content of P.armandii forest in Qinling Mountains also has the highest sensitivity to temperature.The stand density is the optimal factor for the change of available phosphorus content in the soil,and the soil available phosphorus content of P.armandii forest in Qinling Mountains also has the highest sensitivity to the stand density.(5)The growth simulation results show that under the premise of maintaining the current habitat,the growth capacity of P.armandii forests in Qinling Mountains will remain at a good status.In the next five to ten years,the increment of the diameter at breast of P.armandii will be reduced to a stable status year by year.The volume and biomass of the crown will stabilize after a rapid growth in the next five to ten years.The growth rate of branches,bark,trunks and total biomass has gradually slowed down in the next five to ten years,then followed by rapid growth.The P.armandii forest gradually entered the maturity stage,that is,the P.armandii forest will enter the rapid accumulation period of total biomass,and will maintain a high carbon sink capacity for a long period of time in the future. |
