| Stand spatial structure,non-spatial structure,stand regeneration and soil and stand growth are important components of forest structure.Tending felling can have the most direct impact on the structure of the forest,which can better explore the impact mechanism of tending felling on forest stands and provide a reference for sustainable forest management.In this study,the natural Larix gmelinii forest plots with different tending intensities(control(CK),light logging(average 14.96%),moderate logging(average 28.96%),and heavy logging(average 43.80%))were selected as the research object.In August 2012,a total of 18 representative forest plots were selected at the Xinlin Forest Farm of the Xinlin Forestry Bureau in Daxinganling District,Heilongjiang Province for understory tending of young and middle-aged forests and the sample plots of Xinlin Forest Farm and Cuigang Forest Farm were investigated in September 2015 and July-August 2019.The spatial structure,non-spatial structure,stand regeneration diversity,soil and stand growth and other stand characteristics under different tending intensities were compared and analyzed,and the structural equation model was used to study the effects of tending logging on the spatial structure,non-spatial structure,and the impact of stand regeneration and soil and stand growth in order to provide a theoretical basis for production practice.The main conclusions are as follows:(1)The indicators selected for each stand feature can well represent stand spatial structure,non-spatial structure,stand regeneration and soil,etc.(p<0.05),and the cumulative contribution rate of the factors all reach 90%.Correlation analysis showed that the forest competition index has a high correlation with other spatial indicators(p<0.01),the forest diversity index and the regeneration diversity index have a high correlation(p<0.01),and the forest tree density and the regeneration tree density are relatively high(p<0.01).There is no correlation with diversity index(p>0.05).The correlation between soil organic matter and nitrogen content in soil is relatively high(p<0.01).(2)Tending felling can promote the growth of forest stands,and the plots with moderate tending intensity were the best.The diameter at breast height increased in 12-15 years and 12-19 years were 0.87 and 1.58 cm,respectively,and the growth rate at breast height is 9.22%and 16.74%.The accumulated growth were 1.92,3.70m3,and the accumulation growth rates were 28.79%and 55.41%.The accumulation growth of Larix gmelinii in each plot was higher than that of Betula platyphylla,while the growth of diameter at breast height of the light-loving tree species Betula platyphylla was higher than that of Larix gmelinii.(3)When analyzing the regeneration of different height levels,the forest regeneration is divided into three levels according to height,level I:plant height≤60cm;level II:60cm<plant height≤200cm;level Ⅲ:plant height>200cm.The number of grade Ⅰ regeneration in each tending level plot was 0,3,7,and 1,respectively,the number of grade Ⅱ regenerationwas 8,45,41,28 plants,and the number of grade Ⅲ regeneration was 24,53,45,and 60 plants,respectively.There is a lack of level Ⅰ height regeneration in different tending plots,and the number of levelⅡ and Ⅲ height regeneration are significantly higher than that of level Ⅰ(p<0.01).There was no significant difference in in the number of updates of light,moderate,and severe tending intensity plots(p>0.05),but it was increased compared with the control plots.(4)The fitting results of the structural equation model showed that the spatial structure,non-spatial structure,stand regeneration diversity and stand soil characteristics were positively correlated with stand unit accumulation,and the path coefficients were 0.440,0.234,0.096,0.104,respectively..(5)Tending felling had varying degrees of impact on stand spatial structure,non-spatial structure,stand regeneration,stand soil and growth.Taking all factors into consideration,this study believes that the comparison results of various tending plots are as follows:moderate tending plot>severe tending plot>light tending plot>control plot. |
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