Relationship between stand spatial structure and DBH increment of principal species in natural spruce-fir mixed forest in Changbai Mountains of northeastern China

  Objective  The stability and development possibility of mixed forest are closely related to its spatial structure. Exploring the influence of spatial structure on stand growth plays an important role in promoting the benign development of forest.

  Method  Based on the 5 periods of monitoring data of two fixed sample plots, the proportion of spruce (Picea jezoensis) accumulation in the sample plot was 0.1−0.2 and 0.4, respectively, which were recorded as 1P and 4P. The three parameters of spatial structure were calculated by 4 adjacent tree methods, and the multivariate distribution map was drawn. The changes of DBH increment of spruce, fir (Abies nephrolepis) and Korean pine (Pinus koraiensis) under different diameter classes, mingling degrees and neighborhood comparison in 1P and 4P were compared and analyzed.

  Result  1P and 4P were both medium and strong mixed (M was 0.625 and 0.657, respectively) and randomly distributed. The growth of fir and Korean pine was between sub-dominant state and median state (U = 0.25 − 0.50), the growth of spruce was between sub-dominant state and median state (U = 0.48) in 1P, and was between median state and inferior state in 4P (U = 0.70). The annual DBH increment of spruce and fir increased with the increase of DBH class (P < 0.05) and the mingling degree of subject trees, and the DBH increment of small-diameter spruce and large, medium and small diameter’s fir was significantly correlated with mingling degree (P < 0.05). The annual DBH increment of spruce, fir and Korean pine decreased with the increase of subject trees’ neighborhood comparison, and the correlation between the DBH increment of mid-diameter tree and dominance was significant (P < 0.05). The annual DBH increment of spruce in 1P was lower than that in 4P cloud, while that of Korean pines was opposite.

  Conclusion  There are significant differences in the growth of trees under different diameter classes. Reducing the neighborhood comparison and appropriately increasing the mingling are beneficial to the DBH growth of trees. The competition in different growth stages leads to the difference in the response of different diameter classes to mingling degree and neighborhood comparison. Therefore, different management measures should be taken to adjust and optimize the stand structure to promote the long-term stable development of stand.