Spatial Structure Characteristics And Their Influence On Productivity Of Typical Natural Forest In Lingkong Mountain,Shanxi Province

In this study,three typical natural forests in Lingkong Mountain of Shanxi were selected,and nine representative forests of Quercus wutaishanica forest,Pinus tabuliformis forest,and Betula platyphylla and Larix principis-rupprechtii in mixed forest were selected with similar site conditions and neat forest.Based on the investigation and analysis of the typical forest stand community structure and spatial pattern in the study area,and selected uniform angle index（W）,mingling index（M）,dominance index（U）,crowding index（C）,and storey index（S）to characterize the stand spatial structure.Besides,the study estimated the stand productivity through annual ring width and explored the impact of natural forest spatial structure on stand productivity by using redundancy analysis.And based on the stand spatial structure optimization object function（FSI）,it simulates and optimizes the forest stands with poor structure,which provides a theoretical basis for the restoration,reconstruction,protection,and sustainable management of forest vegetation in the Lingkong Mountain area of Shanxi.The result shows:（1）The tree species composition of the Betula platyphylla and Larix principis-rupprechtii forest in the three typical natural forests of Lingkong Mountain in Shanxi is relatively rich.The average diameter at breast height from high to low is:Pinus tabuliformis forest,Quercus wutaishanica forest,and Betula platyphylla and Larix principis-rupprechtii forest.Among them,the Betula platyphylla and Larix principis-rupprechtii forest has a normal distribution of diameter steps.The diameter distribution of Pinus tabuliformis forest presents a"J"shape,which is generally better than that of Quercus wutaishanica forest and Betula platyphylla and Larix principis-rupprechtii forest.The average height from high to low is:Pinus tabuliformis forest,Betula platyphylla and Larix principis-rupprechtii forest,and Quercus wutaishanica forest.（2）The spatial structure characteristics of the three forest stands are similar but slightly different.The similarity lies in the fact that the three forest stands all present an aggregated horizontal pattern and a moderately mixed state,with a relatively high density and a relatively simple vertical structure.The difference lies in the slightly disadvantaged status of Quercus wutaishanica forests,while the Pinus tabuliformis forest and mixed forests are in a moderate state（U₁=0.502,U₂=0.471,U₃=0.500）.Among them,the dominant species of the mixed forest is Betula platyphylla in a disadvantaged state,while the Larix principis-rupprechtii is in a relatively dominant state.In addition,the degree of isolation of tree species in the mixed forest was significantly greater than that of the other two forests（P<0.05）.The degree of density from high to low was as follows:Betula platyphylla and Larix principis-rupprechtii forest>Quercus wutaishanica forest>Pinus tabuliformis forest（C₁=0.955,C₂=0.994,C₃=0.902）.From high to low,the degree of vertical structure is as follows:Betula platyphylla and Larix principis-rupprechtii forest>Quercus wutaishanica forest>Pinus tabuliformis forest（S₁=0.408,S₂=0.419,S₃=0.530）.（3）The bivariate distribution of forest stand spatial structure can more accurately describe the proportion of good and bad structural units in the forest stand,so as to carry out corresponding tending measures.The W-M and W-U bivariate distribution characteristics of the three forest stands are basically similar,and they all show obvious normal distribution with W=0.5 as the axis.There is a big difference in the bivariate distribution of the M-U.Among them,the relative frequency value of the size dominance index decreases with the increase of the mingling index in Quercus wutaishanica forest and Pinus tabuliformis forests.However,the relative frequency of Betula platyphylla dominance index in mixed forest increased firstly and then decreased with the increase of mingling index,while the trend of Larix principis-rupprechtii was not obvious.（4）The stand spatial structure can effectively explain the change in stand productivity.The stand productivity of Quercus wutaishanica forest was positively correlated with U significantly（P<0.01）,negatively correlated with W,C,M,and S,and U was the main driving factor in spatial structure index（the accountability reaches 50.7%）;the stand productivity of Pinus tabuliformis forest was positively correlated with U,C,and M,negatively correlated with S,and negatively correlated with W significantly（P<0.05）and W was the main driving factor in spatial structure index（the accountability reached 57.1%）;the stand productivity of Betula platyphylla and Larix principis-rupprechtii forest was positively correlated with U,W and M,negatively correlated with C and S,and negatively correlated with S significantly（P<0.05）and S was the main driving factor in spatial structure index（the accountability reached 29.3%）.（5）Based on the stand spatial structure optimization object function（FSI）of three typical forests stand spatial structure,the FSI value of Betula platyphylla and Larix principis-rupprechtii forest is the lowest,that is,the structure is relatively better,followed by Quercus wutaishanica forest and Pinus tabuliformis forest.Among them,Pinus tabuliformis forest No.1,No.7 and No.7 Plot No.8 has the worst spatial structure.After ecological thinning,the uniform angle index of each plot is closer to a random distribution（W=0.5）,the degree of mingling index has also been improved,and the overall forest stands are developing in a dominant direction.