Quantitative Analysis Of Spatial Structure And Growth In Spruce Fir Broad-leaved Mixed Forest

Mixed forest has complex structure and rich species diversity,with higher economic,social and ecological value than pure artificial forest.In the history of forest management,the management method of gradually transforming pure artificial forest into multi-layer,different age and mixed forest has been formed in theory.Understanding the complex spatial structure of natural mixed forests,analyzing the effects of different management measures on spatial structure and the relationship between spatial structure and individual trees and stand growth are particularly important for accurate forest management.For this reason,12 plots of 1 hectare spruce-fir broad-leaved mixed forest plot in Jingouling Forest Farm,Wangqing Forestry Bureau,Jilin Province were taken as the research object,and judged the goodness and effectiveness of the classification of three forest layers of three forest layer quantitative division methods under different sampling areas and different adjustment parameters,and then determined the optimal forest layer quantitative division method and parameters;Based on the structural unit with 1 object tree and 4 nearest adjacent trees to construct structural unit type that can reflect finer spatial structure,and compared with the classical structure unit parameters（Uniform angle,Dominance,Mingling and Crowding）and free-to-growth structure index,to analysis the relationship between spatial structure and increment in individual level;Based on the triangular units that constituted the Delaunay triangle network,to construct triangular unit type which is similar to the structural unit type,and compared with the mean value of classical structure unit parameters and structural complexity index,to analysis the relationship between spatial structure and increment in stand level.Based on the structural unit parameters and structural unit type,the spatial structure changes caused by different management measures（crop tree management 1 CTR1,crop tree management 2 CTR2,traditional management TM and control CK）at the individual level were analyzed;Based on mean value of structure unit parameters and triangle unit type,the spatial structure changes caused by different management measuresat the stand level were analyzed.The main research results are summarized as follows:（1）In the method of adjusting top height（Topht）,the minimum number method is the best,when the lower limit value of tree height（Hmin）is 4m,6m and h₀,the number of forest layer division and the goodness of layer division are the best,but the lower limit value of the optimal tree height（Hmin）satisfying the effectiveness of forest layer division is 12m;In the method of light competitive height TSTRAT,when the cut-off coefficient（c）is 0.4 and 0.5,the number of forest layer division and the goodness of division are the best,but the optimal cut-off coefficient（c）meet the requirements of forest layer division is 0.6 and 0.7,when the sampling area is greater than 0.09 ha,0.6 is the best,when the sampling area is less than or equal to 0.09ha,0.7 is the best;In the method of overlap canopy（LMS）,when the overlap constant k₀is 7 m,the number of forest layer division and the goodness of division are the best,but no forest layer divided by any overlap constant can fully meet the judgment of the effectiveness of forest layer division.The optimal method of forest layer quantitative division of spruce fir broad-leaved mixed forest is adjusting top height（Topht）of combined 12m of the lower limit of tree height and the minimum quantity method.（2）Among the structural unit parameters,from the upper layer to the middle layer and then to the lower layer,the angle scale has almost no significant effect on the individual growth,but the object trees in the aggregated structure may have a higher growth amount;but the influence of size ratio,mixing degree and density on the individual growth is more and more obvious,the growth of the trees in the dominant position,with extremely strong mixing and wide growing space was the largest,which was consistent with the expectation.Releasing free to growth space,the height growth was promoted for small diameter class,and the radial growth was promoted for medium and large diameter class.Releasing free growth space has little effect on the growth of birch,Betula platyphylla,Acer mono and Fraxinus mandshurica,medium effect on the growth of Tilia amurensis and Larix olgensis,and the greatest effect on the growth of Korean pine,Abies koraiensis and Picea schrenkiana;Korean pine is suitable for three directions,while Tilia amurensis,Abies koraiensis and Picea schrenkiana are suitable for four directions.Increasing two directions of free growth space is more likely to produce significant growth enhancement effect than increasing only one direction.（3）The relationship between growth the and mean value of spatial structure parameters,their respective value types was affected by stand density.The Angle scale density was larger,the mixing degree was general,and the size ratio was not regular.For the average individual trees growth of stand,the mean value of Uniform angle was positively correlated with it,and the mean value of Dominance was negatively correlated with it.The mean value of Mingling was positively correlated with the mean value of mixing degree,and the more type of 1,the higher the growth amount was.The mean value of Crowding is negatively correlated with the mean value of density.The less type of value 1 is,the higher the growth quantity is.The relationship between the mean value of parameters of each structural unit and each value type and average individual trees growth of stand is consistent with the theoretical trend.（4）Based on the analysis of the influence of stand structure types and stand triangulation types on stand growth,it is concluded that increasing structure diversity of forest layer can improve stand productivity.By analyzing the effects of species group structure types and species group triangulation types on stand growth,it is concluded that promoting the forward succession of stand to increase the proportion of top species is an effective means to improve the growth capacity（5）The change degree of stand spatial structure was TM>CRT2>CRT1>CK,and there was a great correlation between stand spatial structure and management cutting intensity.The results showed that CK and TM increased the degree of community aggregation,while CRT1and CRT2 increased the degree of community aggregation;different management measures had no obvious effect on the degree of size differentiation;all management methods improved the intraspecific competition and crown compression competition.The results showed that the three kinds of management and cutting methods could promote the stand to develop in the direction of better spatial structure,but CRT1 had the best effect.（6）The analysis results of species group structure types and species group triangle types showed that,regardless of the management mode,its development direction or goal is to promote the positive succession of the community.The intraspecie competition between pioneer and associated trees is weak.The composition types of trees with stronger internal competition in the top trees indicated that the community was in a process of positive succession.The associated tree species were suitable for updating into the boundary near more of the same species group,while the top species were suitable for updating into the boundary near a moderate number of the same species group（7）The results of both the size structure types and the size triangle types showed that the growth and development law of the spatial structure of stand tended to be complex was the same regardless of the management mode.In the traditional management,the cutting mainly aimed at the overall structure of stand or the optimization of competition,while the crop tree management focused on the optimization of the crop tree subject to competition.The death of trees is generally more affected by trees of the same size class,followed by the convergence of larger trees.The regenration regeneration ingrowth are often aggregated.