Objective A comprehensive index of stand spatial structure based on adjacent trees was constructed to evaluate the advantages and disadvantages of stand spatial structure and guide the optimization of stand structure.

Method Based on the interpretation of the mean values of stand spatial structure parameters of uniform angle index, crowding, neighborhood comparison and mingling, they were assigned and standardized to make them positive indicators; the average value of mingling is a positive index, and the measured value is adopted; Then the stand spatial structure parameters were combined with the unit circle method to construct the stand spatial structure comprehensive evaluation index (FSS), and its effectiveness was verified by different stand types.

Result The evaluation results of 47 sample plots in 4 regions of China using the constructed spatial structure comprehensive evaluation index showed that: 1) The spatial structure of natural pure forests under extreme site conditions was the worst among natural forests; 2) The spatial structure of natural mixed forest was better than that of artificial mixed forest; 3) The stand spatial structure of mixed plantation is obviously better than that of pure plantation; 4) The spatial structure of natural pure forest was better than that of artificial pure forest.

Conclusion The comprehensive evaluation index of stand spatial structure can evaluate the advantages and disadvantages of stand spatial structure, and can scientifically express the general understanding that "the spatial structure of natural mixed forest is superior to that of artificial mixed forest, artificial mixed forest is superior to that of artificial pure forest, and natural pure forest is superior to that of artificial pure forest". It is a better comprehensive measure index of stand spatial structure, and has guiding significance for optimization of stand spatial structure and effect evaluation.