| The spatial structure and forest growth of stands are an important part of near-nature management.This paper takes four typical forest types of Qinghai spruce forest and its mixed forests as the research object in the hilly forestry area of Taergou,Datong County,Qinghai Province.Analyzing the spatial structure characteristics of forest stand size by Voronoi neighborhood analysis,such as neighborhood comparison,mingling,uniform angle and competition index.Comparing the growth and development rules of the spruce forest.The correlation analysis between structural index and its radial growth index is used to study the influence of spatial structure of spruce forest on radial growth in near-natural state,which provides theoretical basis for regional forest structure optimization and sustainable forestry development.The main conclusions are as follows:(1)The typical types of four spruce stands,the density is 1825-4025 plants/hm~2,the basal area of breast-height is 13.42-42.16 m~2/hm~2,and the average DBH and average tree height of spruce are 7.62-11.79 cm,6.40-10.96 m.Pure spruce forest is superior to mixed forest in terms of basal area of breast-height,average breast diameter and average tree height.In the mixed forest,the average DBH and tree height of the spruce are obviously weak.There was no natural regeneration in the forests of coniferous forests,and there were naturally regenerated plants in coniferous and broad-leaved mixed forests.Among them,the mixed forest of cedar and birch 2,the density was 3175 plants/hm~2,the mixed ratio of spruce and white birch was 1:2,the average tree height of spruce species was 6.40 m and the white birch was 11.71 m.The canopy of forest stands showed obvious stratification.There are significant-differences among the individual trees.The dominant species,white birch,occupies the main forest layer of the canopy,and the pressed wood is obvious.The spruce and white birch have more natural regeneration,which belongs to the quality selection stage of natural succession of forest,and the near natural state is better.(2)Analyzing the spatial structure of forest stands of different forest types from four aspects:neighborhood comparison,mingling,uniform angle and competition index.The tree height,DBH and crown neighborhood comparison of each forest type were consistent.The pure forest of spruce had the highest degree of differentiation from three aspects,the lowest degree of differentiation of the mixed forest of pinus sylvestris.The spruce is at a disadvantage in all mixed forests.The degree of mixing of the mixed forests were all moderately mixed,and mixed forest of spruce and larch of the mixed forests were the best,followed by the mixed forest of spruce and birch,and the mixed forest of spruce and poplar was the worst.Absolutely uniform trees were not found in each type of forest,and the forests were mainly random distribution and aggregate distribution.The hegyi competition index and the crown competition index have a good consistency with the results of the forestry competition analysis.The competition pressure of the pure spruce forest is the lowest,and the competition pressure of the mixed forest of spruce and larch is the largest.Among the mixed forests,the average competition index of spruce species was higher than that of other mixed species,and the spruce species in mixed forest was in a disadvantage.The hegyi competition index is less than 5%in the pure spruce forest and higher in the mixed forest.The crown competition index is also higher in the mixed forest than in the pure forest.This shows that the mixed forest is more in line with the natural selection of the survival of the fittest.(3)The radial growth of spruce in coniferous forest and coniferous and broad-leaved mixed forest is largely different.The trend of Current annual increment of spruce in spruce forest and mixed forest of spruce and larch was consistent.It rose first and then decreased in 2003-2017.The spruce forest reached a maximum of 3.51 mm in 2007.The mixed forest reached a maximum of 3.38 mm in 2009.The growth trend of spruce in the mixed forest of spruce and white birch and mixed forest of spruce and poplar was also consistent.The performance in 2003-2017 was firstly decreased and then increased.In 2016,the maximum reached 2.74 mm in the mixed forest of spruce and white birch.In 2016,the maximum value of 3.25 mm was reached in the mixed forest of spruce and poplar.The perennial growth of spruce is higher in the coniferous forest than in the coniferous and broad-leaved mixed forest in the early growth stage,and the coniferous and broad-leaved mixed forest is superior to the coniferous forest in the late growth stage.The annual growth trend of the basal area of breast-height of spruce in the pure spruce forest and the mixed forest of spruce and larch was consistent.It rose first and then stabilized in 2003-2017.The pure spruce forest reached the maximum of 9.20 cm~2 in 2007.The mixed forest of spruce and larch reached a maximum of 9.22 cm~2 in 2009.The annual growth of basal area of breast-height of the spruce in the mixed forest of spruce and white birch and the mixed forest of spruce and poplar was consistent,and it showed a gradual increase in 2003-2017.In the mixed forest of spruce and white birch,the maximum value reached 8.82 cm~2 in 2016.The mixed forest of spruce and poplar reached a maximum of 12.51 cm~2 in 2016.The annual growth of spruce's basal area of breast-height is higher than that of coniferous and broad-leaved mixed forest in the early growth stage,and the coniferous forest is gradually surpassed in the coniferous and broad-leaved mixed forest in the late growth stage.(4)Correlation analysis of the spatial structure index of the stands and the radial growth index of the spruce stands and curve fitting regression.The results showed:the DBH?average annual growth of the DBH and average annual growth of the basal area of breast-height of the spruce stands had a good correlation with the neighborhood comparison.The neighborhood diameter comparison was better than the height and the crown neighborhood comparison,which was extremely significant.Correlation,the curve is most suitable by polynomial function fitting.The second is the competition index,the hegyi competition index is better than the crown competition index,which is a very significant negative correlation.The DBH and the basal area of breast-height curves are better fitted by the power function.The average annual growth of the DBH was better fitted by the logarithmic function.the mean distance was significantly positively correlated with the annual growth of DBH,but the correlation was lower,and the curve fitting was better using logarithmic function.The correlation of the mingling and uniform angle are not significant with radial growth of the spruce stands.(5)Multivariate linear regression analysis was carried out on the spatial structure index and the radial growth index of spruce stands by stepwise analysis.The results show that the most relevant neighborhood diameter comparison is always the first to enter the model equation,which is the best predictor of radial growth of spruce stands. |
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