Effects Of Tending And Thinning On The Spatial Pattern And Carbon Distribution Of Daxing’an And Xiaoxing’an Mountains

Reasonable tending thinning can improve the forest ecosystem and stand structure,accelerate the growth of trees,increase the biomass of stands,increase the carbon density of stands,obtain higher environment ecological benefits.The natural secondary mixed forest of larch and birch in Daxing’an Mountains and the natural secondary mixed forest of broad and leaved in Xiaoxing’an Mountains were two typical forests in Daxing’an and Xiaoxing’an Mountains.Carried out different intensities of tending thinning of natural forests in Daxing’an and Xiaoxing’an Mountains,adjusted the spatial structure to improve the growth environment of retained trees,and improved forest health and stand stability.Spatial distribution pattern and carbon density distribution characteristics of stands under different tending thinning intensities were investigated and analyzed,and the effects of competition index and thinning intensity factors on the variation of stand carbon density were explored.It provided a theoretical basis for the rational management of forests and was of great significance to the development of forestry carbon sinks.The thinning intensities in Xiaoxing’an Mountains were approximately 15%,25%and 35%,and that in Daxing’an Mountains were 16.7%,25.5%,34.4%,49.6%and 59.9%.Sampling survey method and O-ring statistical method were used to carry out the study,and the main results were as follows:(1)Tending thinning caused the diameter class distribution curve of coniferous in the natural secondary mixed forest of broad and leaved in Xiaoxing’an Mountains;In the control group and the plots with thinning intensity of 15%,25%and 35%,the total stand and the dominant tree species were mainly distributed randomly.Thinning changed the spatial distribution pattern of small scale(0-4m)from random to aggregate,and also changed the distribution state of dominant tree species.The spatial correlation of dominant tree species was changed from partial negative correlation to non-correlation or partial positive correlation,and the competitive pressure was reduced.In the 35%thinning intensity plots,the phenomenon of negative correlation among dominant tree species at 0-25m scales were the least.(2)The frequency curve of larch diameter step in the natural secondary mixed forest of larch and birch in Daxing’an Mountains was normal in the control group and 49.6%thinning intensity plots,while,16.7%,25.5%and 59.9%thinning intensities caused the curve to deviate from normality.With the increase of thinning intensity,the aggregation degree of larch changed,showing a trend of decreasing first and then increasing.When thinning intensity was 49.6%,there was no aggregation distribution at scales(0～20m).In the control group,16.7%plots and 34.4%thinning intensity plots,there was a negative correlation between small size larch and medium diameter larch.There was niche competition and the community structure was not stable.However,the competition pressure of medium and small larch in 25.5%,49.6%and 59.9%thinning intensity plots was small.There was no correlation between medium and large diameter larch in all thinning intensity plots.(3)The total biomass and carbon density of the natural secondary mixed forest of broad and leaved in Xiaoxing’an Mountains recovered well after 8 years of thinning with 35%intensity.However,the total biomass and carbon density of 15%and 25%thinning intensities were significantly lower than those of the control group,and the recovery was poor.The percentage of total carbon density increased first and then decreased with the increase of thinning intensity,and reached the maximum at 15%thinning intensity,while the percentage of total carbon density in branches was just the opposite.The competition index and mean nearest distance showed consistent competition intensity in all regions,all of which were T15>CK>T25>T35;Redundancy analysis(RDA)showed that competition index and thinning intensity accounted for 74.6%of the variation in carbon density,of which competition alone accounted for 27.4%,thinning intensity alone accounted for 21.1%,and the two factors together accounted for 26.1%.The thinning intensity and competition stress responded by changing the carbon density of each organ of the population.(4)When the thinning intensities were 16.7%,25.5%,34.4%,49.6%and 59.9%,the total biomass and carbon density of the natural secondary mixed forest of larch and birch in Daxing’an Mountains both decreased.However,there was no significant difference in biomass and carbon density among 16.7%,49.6%thinning intensity plots and the control plots,and 49.6%thinning intensity improved the utilization rate of forest resources per tree,accelerated the growth of trees,increased the average DBH and average tree height,shortened the mature time of trees,and recovered the biomass and carbon density well.When thinning intensity was 59.9%,the percentage of trunk carbon density in total reached the maximum,while the percentage of branch carbon density was the minimum.However,the change of thinning intensity did not significantly change the percentage of leaf carbon density.RDA ranking results showed that competition index and thinning intensity explained 85.7%of carbon density changed,among which competition alone explained 31.7%,thinning intensity alone explained 27.6%,and the two together explained 26.4%.