The structure and soil characteristics of a Pinus tabuliformis planted forest after 60 years of natural development in North China

This study evaluated the transformation of a Pinus tabuliformis Carriere forest into a near-natural forest after 60 years of natural development. The structure and soil characteristics of P. tabuliformis planted forest, the near-natural forest (coniferous-broadleaved P. tabuliformis mixed forest), and secondary forest (Quercus mongolica Fisch. ex Ledeb. forest) were compared. Tree, shrub and herb species diversity of the mixed and Q. mongolica forests was higher than that of the planted P. tabuliformis forest. Examination of soil characteristics revealed that compared to the pure pine forest, nitrogen (N) and phosphorus (P) concentrations of the mixed and Q. mongolica forests increased in the forest floor and soil, but total carbon (C) concentration decreased in the forest floor, countered by increases in the soil. Furthermore, soil cation exchange capacity (CEC) and pH in the P. tabuliformis forest increased when deciduous broadleaved species were present. Total microbial biomass and bacterial biomass in the soils were greatest in the Q. mongolica forest, followed by the mixed, and then the P. tabuliformis forests. However, fungal biomass did not significantly differ among the three forests. Overall, the findings of this study suggest that different forest types can affect soil microbial biomass and community structure. Meanwhile, the natural development is recommended as a potential management alternative to near-natural transformation of a P. tabuliformis planted forest.