Study On Environmental Factors And Natural Regeneration Of Gap In Chinese Pine Plantation

Chinese pine(pinus tabulaeformis)is the main afforestation tree species in northern China.It has the characteristics of drought resistance,barren tolerance,light likeness,etc and has the functions of maintaining water and soil,conserving water sources,providing materials and improving soil.However,Pinus tabulaeformis plantation forests are facing a single stand structure,simple stand heterogeneity,and most stands are in mature forest stage,so the problem of regeneration is imminent.It is generally believed that there is a close relationship between gaps and natural regeneration,so what is the relationship between gaps and natural regeneration in Chinese pine plantations? To solve this problem,We established four forest gap classes based on the forest-gap breadth to the average height(H)of surrounding trees,which was classified into small(0.75H),mediun(H),large(1.25H)gaps and closed canopy reference plots(CK)in a plantation.Three repetitions were set for each gap size class.Each gap was divided into B(gap center area),C(gap edge area)and D(gap surrounding area).We investigated the regeneration performance of Chinese pine and measured the environmental factors(photosynthetically active radiation,air temperature,air humidity,soil temperature and soil humidity)during the growth peak season.The results of the study first elaborated the differences in species composition,growth status and environmental factors at different gap sizes,and the relationship between the growth status of regenerated seedlings and environmental factors;second elaborated the internal mechanism of the effect of natural regeneration,to explore the relationship between environmental factors and the growth of Chinese pine seedlings.The main research contents and results are as follows:1.The effect of different gap sizes on the growth status and pattern of regenerated seedlings(1)The number of regenerated Pinus tabulaeformis seedlings in all gap classes accounted for most of all plant species,> 82.6%,and the proportion of regenerated Pinus tabulaeformis seedlings was not significantly different(p> 0.05),indicated that Creating gaps in planted forests does not change the composition of plant species in Pinus tabulaeformis plantation forest.(2)The gap size has a significant effect on the average density(ALL),average height and average growth of the current year(p <0.05).The maximum density of Pinus tabulaeformis seedlings in all gaps was always located in the C area.(3)The distribution of seedling age is almost normal,and the age of renewed seedlings is mainly concentrated in the range of 3-10 a.The seedling age of most individuals is 5a,6a,7a and 8a.The number of younger seedlings in all gaps is larger than that of younger seedlings.(4)Nuclear density analysis shows that the density of renewing seedlings in all gaps of the gap is generally the smallest in the marginal area of the gap;seedlings and young trees at all gap levels that is a clear positive correlation between them,that is to say,the seedlings and young trees tend to gather and distribute.2.The impact of different gap sizes on environmental factors(1)The photosynthetically active radiation and soil temperature between different grade gaps reached significant differences(p <0.05)and increased with the increase of the gap area.(2)Photosynthetically active radiation showed significant differences among different areas of the three area grades.The soil temperature reached a significant difference only in the L-II area grade gap(p <0.05).the photosynthetically active radiation and soil temperature have maximum values in the central area of gaps.(3)the gaps and gap areas of different levels produced by thinning has a significant impact on photosynthetically active radiation and soil temperature,and have little effect on other environmental factors in Chinese pine plantation.3.Correlation analysis of regenerated Pinus tabulaeformis seedlings and environmental factors(1)Person analysis showed that photosynthetically active radiation and soil temperature was the main factors affecting the regeneration status of the regenerated seedlings in the forest gap.(2)GAM model analysis shows that Photosynthetic effective radiation has a significant effect on the density of regenerated seedlings in all gaps,(3)Analysis of the logliner model based on the point pattern of spatial coordinates shows that photosynthetically active radiation and air humidity was the main factors affecting the spatial distribution of the regenerated seedlings in small gaps of Chinese pine planatation;the photosynthetically active radiation,air temperature and air humidity coefficient all reached extremely significant levels in the middle forest gap;The coefficients of the five environmental factor models in the large gaps have reached significant differences.