Effects Of Induced Transformation On Structure And Ecological Function Of Low-Quality Forests In Daxing'an Mountain

As an important forest barrier in China,Daxing'an mountain has an irreplaceable ecological role.Due to the early unreasonable management and over cutting,a large number of low-quality and inefficient forests have been formed.The implementation of the natural forest protection makes the forest resources recovering and improving effectively,but on the whole,the quality of forest resources is still low,and the function of ecological environment is still weak.This paper selects three kinds of typical forest stands after induced transformation in Daxing'an mountain,analyzes the restoration state of ecological environment,in order to master the dynamic process of ecological environment restoration after induced transformation of different low-quality and low-efficiency forests,improve the productivity and quality of forest stands,provide scientific reference for the sustainable management of low-quality and low-efficiency forest in Daxing'an mountain,and promote forest resources recovery and promotion.In this paper,the coniferous and broad-leaved mixed forest,Quercus mongolica forest and Betulaplatyphylla forest in Daxing'an mountain were taken as the research objects,and the banded transformation of different bandwidths was carried out,including 6m(S1),10m(S2),14m(S3),18m(S4),and three seedlings of Larix gmelinii,Pinus sylvestris and Pinus koraiensis were planted respectively,and the uncut plot was set as the control plot(CK).At the same time,five sample plots were randomly set up in each forest subarea to determine the species name,tree height,DBH,crown width and position coordinates.Continuous observation(2010-2018)was carried out on the indicators of soil chemical properties,hydrological efficiency of soil layer,hydrological efficiency of litter layer,canopy structure,photosynthesis,species diversity,growth state of reserved and renewed trees in the transformed sample plots to analyze the temporal and spatial changes of each indicator in different stands.A comprehensive evaluation model was established based on the data at the end of the investigation period to evaluate the ecological environment restoration of different transformed plots.(1)The R software were used to analyze the univariate and binary distribution characteristics of tree height DBH,and Winkelmass software was used to calculate the spatial structure parameters of three low-quality forests.The proportion of small-diameter trees was higher than that of large-diameter trees,and the spatial structure of the three stands was in the form of clusters,with fierce competition.Coniferous and broad-leaved mixed forest had no advantage in tree size and spatial structure.Induced transformation had a greater impact on the spatial distribution of forest stands and accelerates the process of forest succession.(2)The effect of induced transformation on soil chemical properties and hydrological efficiency was analyzed by using the time-varying index and repeated measurement variance.Combined with the litter decomposition model,the effect of induced modification on the hydrological efficiency of litter was analyzed.As of 2018,the soil chemical properties of coniferous and broad-leaved mixed forest and Betula platyphylla forest basically recovered to the original state,but Quercus mongolica forest had not yet recovered to the state before the transformation.The influence of the transformation bandwidth on the chemical properties of soil fluctuated with the change of years,but had no significant influence on the hydrological efficiency of soil layer and the decomposition rate of litter.The relationship between litter volume and interception volume was exponential function with time.The improvement of seedlings had no significant effect on the soil chemical properties,on the hydrological efficiency of soil layers of Quercus mongolica forest and Betula platyphylla forest,but had some significant effect on the hydrological efficiency index of some soil layers of coniferous and broad-leaved mixed forest.The parameters of litter decomposition model of different modified seedlings were different.(3)Single factor analysis of variance(ANOVA)was used to analyze the relationship between canopy structure parameters and photosynthesis parameters of three low-quality forests.The results show that the leaf area index of the three kinds of forest decreased with the increase of the bandwidth,but it was still smaller than that of the sample plot as of 2018.The transpiration rate,photosynthetic rate and stomatal conductance of the undergrowth were higher than those of the others in the strip with of 14m and 18m,which promoted photosynthesis.There was no significant effect on canopy structure and photosynthetic parameters of transformation.There was a significant negative correlation between canopy gap fraction and leaf area index,and there was a positive correlation between photosynthetic rate and transpiration rate.Photosynthesis and transpiration were consistent in time.(4)Single factor analysis of variance(ANOVA)was used to analyze the effects of induced transformation on species diversity and tree growth of three low-quality forests.The zonal transformation had a greater impact on the species diversity index of herbaceous layer,a smaller impact on the species diversity index of arbor layer and shrub layer,promoted the growth of reserved trees in the forest,and the growth of reserved trees was higher.It had great influence on the spatial distribution of forest stand.As of 2018,the continuous growth rate and preservation rate of seedlings tend to be stable,the continuous growth rate of Larix gmelinii,Pinus sylvestris and Pinus koraiensis are smaller,the preservation rate of Larix gmelinii is higher,and the preservation rate of Pinus koraiensis is bwer.(5)In this study,34 indexes of 5 environmental factors,including soil chemical properties,hydrological efficiency of forest land,light environment in forest,species diversity,growth state of reserved and renewed trees,were selected.The weight of the indexes was obtained by subjective and objective comprehensive weighting method,the influence of the transformation method on various environmental factors was evaluated by grey correlation method,and the ecology of various lands at the end of the investigation period was evaluated by fuzzy membership function comprehensive evaluation.The results showed that the coniferous and broad-leaved mixed forest did not return to the initial state of transformation within the investigation period,and the induced transformation of Betula platyphylla forest could improve the ecological environment of the forest.The ecological environment of the three forest stands was the best when the reconstruction bandwidth is 10m,14m and 18m respectively at the end of investigation period,but they were still in the recovery period,and the effect needed to be further verified by long-term observation.