Analysis on Vertical Structure Characteristics of Juglans mandshurica Secondary Forest in Eastern Liaoning Mountainous Area

Taking the secondary forest of Juglans mandshurica in the mountainous area of eastern Liaoning Province as the research object, the stand was divided into upper, middle and lower layers according to the canopy competition height(CCH), and on this basis, the tree species composition, diameter class structure and spatial structure characteristics of each forest layer were analyzed. The result showed that the average tree heights of the upper, middle and lower layers were 14.86−17.02, 11.18−12.77 m and 7.33−8.01 m, respectively. The ANOVA results showed that there were significant differences among tree heights of different forest layers, with excellent layering results. The upper forest layer was the main contributor to the stand volume, accounting for 61.86%−78.7%, followed by the middle layer, and the lowest in the lower layer. The diameter distribution curve differs between forest layers, with the lower layer showing an inverse 'J' curve, the middle layer a left-skewed single-peaked curve and the upper layer a multi-peaked curve. The stand was in a state of transition from moderate to strong mixing. The mean mixedness of the upper and middle layers in 3 samples was 0.512 and 0.574 respectively, which was moderate mixedness, while the mean mixedness of the lower layer was 0.671, which was close to strong mixedness, and the mean mixedness of each forest layer showed an increase with decreasing vertical height. Sample plots 1 and 3 are aggregated and sample plot 2 is randomly distributed. Both stand aggregation and competition index increased as the vertical height of the stand decreased. The secondary forest of J. mandshurica is relatively stable by judging from the vertical structure of the forest, and its future succession direction is likely to be a mixed coniferous forest with Larix gmelinii and J. mandshurica as the dominant species or a mixed broadleaf forest with J. mandshurica, Quercus mongolica and Fraxinus rhynchophylla, where the dominant species J. mandshurica is less capable of regeneration and needs to be artificially promoted for natural regeneration.