The Strategy for Optimizing the Stand Structure of Pinus tabuliformis Carr. Forests to Enhance the Ecological Function on the Loess Plateau, China

Abstract

The enhancement of the ecological functions of forests through stand structure optimization is a key issue for high-quality forestry and its sustainable development on the Loess Plateau. In this study, fifty standard plots of Pinus tabuliformis Carr. forest were established in the Loess Plateau of western Shanxi, China. Eleven factors of the stand structure, three topographical factors, and four functional indices of the ecological function, including 20 sub-functional indices, were investigated and monitored. The study results indicated that the stand structure and topographical conditions could significantly affect the ecological functions of the Pinus tabuliformis forest, which was primarily reflected in the water-holding function, soil improvement function, and diversity function of understory plants, but had little effect on the function of reducing runoff and sediment yield on slope. We found that the stand density and uniform angle index could be used to achieve the optimal regulation of the stand structure to enhance the ecological functions of the Pinus tabuliformis forest. Overall, the optimization strategy for the stand structure of Pinus tabuliformis on the Loess Plateau should be to (1) determine the characteristics of the regulation target by understanding the stand structure and its ecological function characteristics through stand surveys on the altitude of the stand, stand density, uniform angle index of the individual trees in the sample plot, and average uniform angle index of the sample plot; (2) determine the optimization target by quantifying and analyzing the ecological functions of the stand, selecting a certain functional index as the optimization target, and specifying the degree of improvement in the functional index; and (3) substitute the optimization target and elevation of the stand into the corresponding stand structure optimization model and determine the regulation direction and regulation range of the stand density, uniform angle index, and specific stand structure regulation measures. The results of this study serve as a guide for optimizing the stand structure on the Loess Plateau.