Differences in Soil Physicochemical Properties in Different-Aged Pinus massoniana Plantations in Southwest China

With increasing age, plants will cause changes in soil physicochemical properties. The objective of this study was to investigate differences in the soil physicochemical properties in different-aged Masson pine forest plantations (i.e., 10, 20, 40, and 60 years old). Soil samples were collected in a pure Masson pine forest plantation in Southwest China. The soil determination indexes included organic carbon, nitrogen, phosphorus and potassium contents, water content, bulk density, and pH. The soil pH of a 20-year-old forest was significantly (p < 0.05) higher than that of a 10, 40, and 60-year-old forest. In addition, soil-available phosphorus in a 60-year-old forest was significantly (p < 0.05) higher than that in the other three age forest groups. With increasing forest age, available phosphorus increased, while available nitrogen decreased at 20 years old and then increased at 40 years old. There was a significant positive correlation (p < 0.05) between total nitrogen and available potassium; no significant correlation (p> 0.05) between total phosphorus and total potassium, organic carbon, bulk density, and pH; and a significant negative correlation (p < 0.05) between available phosphorus and the water content. The availability and utilization efficiency of soil nutrients in young forests were higher than those in old forests and the intermediate forest age was an important time point that affected the soil properties. To improve the availability of soil nutrients and ensure the sustainable utilization of soil resources, it is necessary to increase the input of nitrogen and especially phosphorus. More attention should be given to the phytochemometric response with respect to the age of plantations.

Close-to-nature management positively improves the spatial structure of Masson pine forest stands

Close-to-nature management (CTNM) has been proposed as a promising forestry management approach to improve the structure and quality of forests, which integrates wood production and ecological service functions. Research on the effect of CTNM on the univariate and bivariate distribution of the spatial structure of forest stands provides a scientific basis for the evaluation of CTNM implemented in forestry. Here, we analyzed and compared the spatial-structure characteristics of Masson pine (Pinus massoniana) plantations (young, middle-age, and near-mature stages) under CTNM 8 years after selective cutting and unmanaged control. We used univariate and bivariate distribution of three spatial-structure parameters: mingling (M), dominance (U), and uniform-angle index (W). Results showed that the effect of CTNM on spatial structure was more remarkable in middle-aged and near-mature Masson pine forests compared with the young forest. CTNM significantly improved mingling degree and promoted the horizontal distribution, thereby changing from a cluster to a random distribution. Moreover, CTNM improved the proportion of trees with a high mixing degree and random distribution and the proportion of trees having a micro-structure of random distribution with a high degree of mixture and dominance with a high degree of mixture in middle-aged and near-mature Masson pine forest. Overall, the implementation of CTNM 8 years ago showed a positive effect on the improvement of the spatial structure of Masson pine forest, but the present spatial structure is suboptimal. Further implementation of CTNM to adjust the mingling and uniform-angle index is necessary, and CTNM according to this method of frequency distribution of stand structure parameters can improve the success of forest management.