Abstract
Pinus massoniana is an important tree species for wind protection and timber forests in Southern China. In recent years, P. massoniana plantations have been developed on more than 11,300,000 hm2 in southern China, but numerous problems have been observed, such as soil degradation, biodiversity reduction, and ecological functional decline. Crop tree management impacts on fine root development, which can be explained by the variations in the root orders. In this study, a 36-year-old P. massoniana plantation located in Huaying, Sichuan Province, was selected as the research field. In 2015, crop tree management was initiated, with a crop tree intensity of 150 trees per hectare. After 3 years of growth, fine roots of crop and noncrop trees were collected by the sector method with an angle of 15 degrees and a radius of 2 meters. We analyzed the morphological characteristics and biomass in different root orders, and explored their carbon and nitrogen contents. The results were as follows: (1) The specific root length (SRL), root length density (RLD), and surface root area (SRA) of the crop trees were larger than those of the noncrop trees; the SRL increased significantly from 0–0.5 m to 1–1.5 m from the stem. (2) The fine root biomass of the crop trees was significantly larger than that of the noncrop trees. The fine root biomass of the crop and the noncrop trees increased with the horizontal distance from the stem from 0–0.5 m to 1–1.5 m. The morphological indexes of the noncrop trees at the distances of 1–1.5 m and 1.5–2 m were significantly different, while those of the crop trees at those distances were not. (3) The fine root C content of the crop trees was significantly higher than that of the noncrop trees and varied significantly along a vertical distribution. The fine root N content of the crop trees was significantly higher than that of the noncrop trees, and the N content of topsoil was higher than that of deeper soil. In conclusion, our results indicated that crop tree management increased the production of a large-diameter wood of P. massoniana, which might be attributed to the improvement of soil permeability and nutrient stock, and thus, the enhancement of fine root quantity and water/nutrient absorption ability.
Highlights
Pinus massoniana, an important shelterbelt and timber species in southern China, has a high economic value and plays an important role in subtropical forest resources and ecological services in China
The diameter of both the crop and noncrop trees decreased with the increasing root orders (GLMs: Wald χ2 = 3852.743, p < 0.001 for the crop orders)
The specific root length (SRL) of P. massoiana crop trees was found to be significantly increased compared to the noncrop trees after 3 years of crop tree management (GLMs: Wald χ2 = 1148.242, p < 0.001 for crop tree management) (Figure 3)
Summary
An important shelterbelt and timber species in southern China, has a high economic value and plays an important role in subtropical forest resources and ecological services in China. Near-natural forestry measures such as crop tree management measures can be effective means to improve the productivity and production efficiency of P. massoniana. Crop tree management suits the goals of foresters and can be beneficial for producing better woods and achieving better economic returns. Crop tree management can take into account ecological environmental requirements and balance the multiple benefits of stands, which is closely connected with the National Forest Protection Projects in China and ecological civilization construction [5]. By performing single-plant selection and management, we can support the ecological functions of the forest, and maintain maximum accumulation and biomass [6]
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