| In order to reveal and grasp the productivity of mixed coniferous forests and its relationship with the non-spatial structure of the stands,the data from two successive forest resource inventories in Zhejiang Province in 2004 and 2009 were used as research materials to calculate the biomass of the stands before and after the two periods based on the single wood biomass model,and the productivity was calculated accordingly.The non-spatial structure of forest stands was characterized from six major structures and 20 indicators.The formation of stand productivity was decomposed into four components,including retained wood productivity,incoming wood productivity,dead wood productivity and harvested wood productivity.Their relationships with non-spatial structure were investigated one by one through correlation analysis and structural equation modeling,and the following conclusions were obtained.(1)The average stand productivity was 3.64 t/(hm~2·a),including 3.40 t/(hm~2·a)for retained wood,2.01 t/(hm~2·a)for incoming wood,-0.81 t/(hm~2·a)for dead wood,and-0.96 t/(hm~2·a)for harvested wood.The average stand productivity was-0.81 t/(hm~2·a)and-0.96 t/(hm~2·a)for harvested wood and-0.96 t/(hm~2·a)for mixed coniferous forests.(2)Stand productivity was significantly and positively correlated with species structure,stocking structure and stand density,and the correlations were in descending order of stand density,stocking structure and species structure,respectively.Among them,the number of plants per hectare,small diameter group accumulation and Simpson index were the most closely related to stand productivity among the structures.In the structural equation model,the effect of stand productivity in relation to non-spatial structure was not clear,and only the Simpson index had a significant combined effect on stand productivity.(3)Retained wood productivity is an important component of stand productivity and is most closely related to the non-spatial structure of the stand.Stand density had a more prominent effect on productivity than other non-spatial structures of the stand,followed by stocking structure,species structure,and tree height structure.Species richness and uniformity of needle and broad comparisons were more closely correlated with retained wood productivity in the species structure,and the size-divergence of the stand was more closely related to productivity than the average diameter at breast height level of the stand.In the structural equation model,squared mean diameter at breast height had the largest combined effect on retained wood productivity,followed by stand density index,Simpson index,mean age,mean height,Shannon size diversity index,and conifer species stocking percentage.Overall,it can be concluded that the higher the number of plants,the higher the diversity level,the higher the average age,the higher the average tree height,the more pronounced the size differentiation,and the lower the percentage of coniferous species accumulation,the higher the retained wood productivity of the stand.(4)Productivity of other components.Younger stands with predominantly coniferous species and much less pronounced stand size differentiation were relatively more likely to have high incoming stand productivity.The older the average age and the higher the number of trees,the higher the amount of dieback in the stand.Stands with more pronounced stand size differentiation,higher average tree height,and higher age are likely to have higher harvesting volumes.(5)In the management of mixed coniferous forests,if we want to improve forest productivity,we should mainly start from increasing the density of forest stands,species diversity and promoting the differentiation of forest size,so as to form a forest stand structure with rich species,obvious differentiation,high density and diverse age.On this basis,effective measures should be taken to scientifically manage and utilize the dead and harvested trees,and timely implement the forest replenishment and renewal. |
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