[Evaluation of the tree form quality of middle-aged Pinus tabuliformis plantation under different canopy densities in Huanglong Mountains, Northwest China].

To clarify the effects of different canopy densities on tree form quality of Pinus tabuliformis, a hierarchical indicator system was structured, which brought about a set of grading criteria to evaluate tree form quality of the middle-aged P. tabuliformis plantation under four canopy densities in Huanglong Mountains by using the analytic hierarchy process (AHP). Plots were divided into four classes according to the stand canopy density (CD) : CD<0.65 (type 1), 0.65≤CD<0.75 (type 2), 0.75≤CD<0.85 (type 3) and CD≥0.85 (type 4). The results indicated that, by comprehensive analysis of ten related indicators, i.e., diameter at breast height (DBH), tree height, diameter height ratio, taperingness, stem straightness, forking ratio, height under living branch, number of branches, max-branch base diameter and average base diameter of branches, the tree form quality could be evaluated. Among these factors, stem straightness, forking ratio and DBH were the most important ones influencing the tree form quality with a total weight of 0.7382. So, these three indicators were the major determinants of tree form quality. The comprehensive scores of the tree form quality evaluations fluctuated as the canopy density decreased and topped at 90.28 when CD was valued at 0.75 (type 2). The indicators and evaluation system developed in this study were easy to operate, and quite fit for solving the quantity problem of the tree form quality evaluation. Our system would be capable for applications in evaluating the tree form quality of other tree species on the Loess Plateau.