Establishment of thinning models for Larix olgensis plantation based on spatial structure optimization

Taking Larix olgensis plantation as the research object, a set of evaluation methods of stand spatial structure optimization was constructed, and based on this, a stand thinning model was constructed to provide a scientific thinning scheme for forest tending management.

After standardized calculation, the forest survey factors such as height, DBH and crown width were weighted to Delaunay triangulation network and the stand spatial competition unit was determined. The six forest spatial structure parameters of sample plot uniform angle index, dominance, crowding, stand open degree, competition index and mingling degree were calculated, and the entropy weight method was used to give the weight of each parameter. Combined with the idea of multiplication and division, the multi-objective programming was carried out, and then the stand spatial evaluation index (SEE) and stand spatial evaluation level (SET) were calculated. Based on SEE, a stand average thinning model was constructed (This model could select the trees with poor spatial structure in the stand and make them more evenly distributed in the stand) and applied to the actual plot. In Dongsheng Forest Farm of Lushuihe Forestry Bureau, 20 square plots of Larix mixed forest with an area of 0.06 hm² were established. The changes of spatial structure parameters, SEE, SET and the canopy projection map of 6 stands before and after thinning were analyzed to verify the rationality of the model.

SEE was applied to the survey stand, and it was found that the mean SEE of the 20 plots was between 0.138 and 0.216, and SET was distributed at level 1 and level 2. Among them, 85% of the plots belonged to level 1, and 15% of the plots belonged to level 2. According to the definition of SET, the stand quality could be judged to be poor, which needed to be optimized. Taking the sample plot z17 with the lowest rating index as an example, after the application of the average thinning model, it was found that the spatial structure parameters of each stand developed in the direction of optimization, and the SET of the sample plot was upgraded from level 1 to level 2.

Based on the weighted Delaunay triangulation, the stand average thinning model constructed by combining the multiplication and division method and the entropy weight method can improve the defects of similar models, optimize the spatial structure of the stand, and has important reference significance for the construction of stand growth and harvest prediction model.