Objective Taking the most suitable main cutting age stand of Pinus tabuliformis construction timber as the research object, starting from the density effect, it is expected to explore the response mechanism of forest growth performance characteristics and soil physical and chemical properties of different forest densities, determine the limiting factors affecting the timber production, improve the cultivation technology of P. tabuliformis construction timber forest in Hebei Province of northern China, and provide guidance for the realization of sustainable forest management.
Method The 50, 52 and 56 years old final felling age stands of P. tabuliformis building forests in Pingquan City, Hebei Province were taken as research objects and divided into three density gradients: 450−750 plant/ha for low density, 750−1 050 plant/ha for medium density and 1 050−1 350 plant/ha for high density. The wood growth characteristics and soil physicochemical properties of three stand densities were studied. Pearson correlation analysis was conducted on each growth performance index and soil physicochemical properties. In addition, factor analysis method was used to calculate the comprehensive score and ranking of P. tabuliformis construction timber stands of each density by combining the growth performance and soil quality, and to evaluate their sustainable management ability.
Result (1) The wood output per unit of stand was not significantly affected by stand density, but decreased with the decrease of stand density. The wood output per unit of high density stand was the highest, which was 107.87 m3/ha. (2) The average output of single tree of low density P. tabuliformis construction timber forest was 0.256 4 m3, and the biomass of tree trunk per unit area was 148.02 t/ha, which was significantly higher than that of medium density and high density (P<0.01), and more than twice that of medium density and high density. The wood yield of single tree and the proportion of trunk biomass of low density stands reached 84.12% and 68.56%, respectively, which were significantly higher than those of medium and high density stands. (3) In soil physical properties, density effect had a very significant effect on soil density, non capillary porosity, saturated water holding capacity (P<0.01), and had a significant effect on soil total porosity (P<0.05); among the soil chemical properties, the density effect only had a very significant effect on soil available potassium (P<0.01). (4) The output per unit area had no significant correlation with other indicators. The average wood yield per tree was significantly positively correlated with the proportion of trunk biomass (P<0.01), and negatively correlated with non capillary porosity (P<0.05). The proportion of trunk biomass was significantly positively correlated with soil bulk density (P<0.05), significantly negatively correlated with saturated water capacity and total porosity (P<0.05), and extremely significantly negatively correlated with non capillary porosity (P<0.01). (5) The comprehensive quality of stand was the highest at the density of 750−1 050 plant/ha, which was most conducive to the sustainable management of P. tabuliformis building timber forest.
Conclusion The trees in low density (450−750 plant/ha) are used to make large-diameter building frame materials, and the trees in medium and high density (750−1 350 plant/ha) are used to make small-diameter spliced materials and furniture, etc. Soil layer mainly affects the chemical properties of soil, while stand density mainly affects the physical properties of soil. There is no significant correlation between wood yield per unit and tree growth performance and soil physicochemical properties. The accumulation of trunk biomass can promote the increase of wood output per tree. The optimal reserve density for sustainable management of P. tabuliformis building timber forest is 750−1 050 plant/ha.