| The spatial structure of trees has an important influence on the growth of trees.This study takes the typical Pinus massoniana mixed forest in Liping County as the research object.According to the mixed tree species and mixed proportion,the typical Pinus massoniana mixed forest in the study area is divided into seven types of stands,namely,Pinus massoniana accounts for 40%(type A),50%(type B),70%(type C)of mixed coniferous and broad-leaved forests,and Pinus massoniana accounts for 30%(type D),50%(type E)70%(type F)coniferous mixed forest mixed with Chinese fir and Pinus massoniana pure forest(type G).The index data of tree height,crown width,diameter at breast height,volume,etc.are obtained through standard survey,and their differences are analyzed.Then,the impact of spatial structure parameters such as angle scale,ratio of diameter at breast height,ratio of tree height to size,and mixing degree on the growth of Pinus massoniana is analyzed.Then,the tree core is drilled with the growth cone to obtain the growth data of diameter at breast height of Pinus massoniana,and the angle scale,ratio of diameter at breast height The research results can provide reference for the management and transformation of mixed forests in the study area.The main research conclusions are as follows:(1)There are significant differences in the growth of various types of Pinus massoniana.Type A of Pinus massoniana coniferous and broad-leaved mixed forest has the largest diameter at breast height,tree height,crown width and volume.Type D of Pinus massoniana coniferous mixed forest has the largest diameter at breast height,tree height,crown width and volume.When Pinus massoniana occupies a small proportion of forest types,its diameter at breast height,tree height,crown width and volume are greater than those of pure forest.The diameter of each type of Pinus massoniana conforms to weibull distribution,and the height of Pinus massoniana of type A,type D and type E conforms to weibull distribution.(4)All types of Pinus massoniana stands in the study area are in light aggregation distribution,tending to random distribution pattern;In type F,Pinus massoniana is in the middle of tree height and diameter at breast height competition state,while other types of Pinus massoniana are in the sub dominant competition state of tree height and diameter at breast height;The mixed degree of tree species in the Pinus massoniana mixed forest is relatively high,usually above the moderate mixed intensity,while the weak mixed degree of pure Pinus massoniana forest is close to zero mixed degree.The comprehensive bid evaluation price of Pinus massoniana mixed forest is superior to that of pure Pinus massoniana forest.(3)The angle scale has no significant correlation with the growth factors of various types of Pinus massoniana trees in each type.The ratio of diameter at breast height and the ratio of tree height to size have significant negative correlation with the growth factors of Pinus massoniana in the mixed coniferous and broad-leaved forests,mixed coniferous and broad-leaved forests,and pure forests.The mixing degree has significant positive correlation with diameter at breast height and single tree volume in the mixed coniferous and broad-leaved forests and mixed coniferous and broad-leaved forests.The growth factors of Pinus massoniana and Pinus massoniana in the mixed coniferous and broad-leaved forests and the mixed coniferous and broad-leaved forests were significantly positively correlated with FSSI,and significantly negatively correlated with FSSD.In the pure forests,there was no significant correlation with FSSI,but significantly negatively correlated with FSSD.(4)The average annual growth of the diameter at breast height of Pinus massoniana presents a normal distribution on different angular scales.The maximum value of the mixed coniferous and broad-leaved forests is concentrated at the angular scale of 0.75,while the mixed coniferous and pure forests are concentrated at the angular scale of 0.5.The average annual growth of the diameter at breast height of Pinus massoniana decreases with the increase of the ratio of diameter to size and the ratio of tree height.Type G is most affected by the ratio of diameter at breast height,Type E is most affected by the ratio of tree height to tree size.On the scale of different mixing degrees,the average annual growth of Pinus massoniana DBH is different from that of other types due to the large difference in the ratio of tree height to size of type A and type E,which shows that the average growth of Pinus massoniana DBH is in the law of intensity mixing>extreme intensity mixing>medium mixing>weak degree mixing>zero degree mixing,The average DBH growth of other types of Pinus massoniana stands increased with the increase of mixing degree.(5)On the scale of angle scale,the growth dynamics of DBH of masson pine of different types and different angle scales are significantly different.With the passage of time,the growth of DBH of masson pine in different spatial distribution patterns gradually differentiated.In the mixed coniferous and broad-leaved forests,the growth of DBH of masson pine in uneven distribution is better,while in the mixed coniferous forests and pure forests,the growth of DBH of masson pine in random distribution is better.In a certain period of time,the competition of Pinus massoniana in the forest is more intense.After the occurrence of self thinning or human interference,the spatial distribution pattern has changed,making the difference of DBH growth between trees gradually obvious.(6)On the scale of size ratio,the average growth of DBH of each stand is not significantly different in a certain period,which indicates that there is fierce competition among trees at this time.The continuous growth of DBH of Pinus massoniana of type A and type D is greater than the average growth again in different periods,while the pure forest shows a fluctuating decline after the average growth reaches the maximum,and the continuous growth is always less than the average growth thereafter,It shows that in type A and type D,mixed forest trees can promote the growth of Pinus massoniana trees to a certain extent.(7)In the perspective of mixing degree,the average growth of each stand in a certain period has no significant difference.Except for zero degree mixing,the continuous growth of Pinus massoniana of the other types of mixing degree fluctuates greatly in varying degrees in 16-26 years,and the fluctuation of continuous growth increases during this period.The average growth of diameter at breast height of Pinus massoniana with type E in weak mixing and medium mixing is less than that of Pinus massoniana with type E in medium mixing 8 years ago.For type B,except for zero degree mixing,the continuous growth of Pinus massoniana at other mixing degrees presents a double peak curve before it intersects with the average growth.Except for zero degree mixing,the continuous growth of Pinus massoniana in other mixing degrees presents a double peak curve before the intersection with the average growth.To sum up,there are differences between the growth and spatial structure of typical Pinus massoniana stands in the study area,and there is a certain correlation between them.The spatial structure of stands has a certain impact on the growth of the diameter at breast height of Pinus massoniana,which is roughly shown as a negative correlation between the average growth of diameter at breast height and the size ratio,and a positive correlation with the mixing degree.However,when Pinus massoniana is higher than the surrounding mixed trees,The effect of mixed forest is offset or even lower by the difference of tree height.Therefore,in the process of mixed forest management and transformation,forest management measures such as thinning and pruning should be taken in time to expand the growth space of Pinus massoniana and promote its growth.The growth of DBH of Pinus massoniana in mixed forests is different from that in pure forests.Affected by mixed forests,the DBH will grow more prominently in a certain period of time.The growth of Pinus massoniana with different dominance is significantly different.The growth of trees with other dominance except for dominant trees is not significantly different in a certain period of time.Therefore,the stands should be thinned during this period to remove the trees with inferior growth and expand the growth space of trees;The growth of Pinus massoniana of different mixing degrees is also different.Compared with zero mixing,the growth of Pinus massoniana of other mixing degrees is outstanding in a certain period.Therefore,the mixed species should be replanted in this period to improve the growth of diameter at breast height of Pinus massoniana. |
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