[Effects of different disturbance patterns on stand structure of infected pure Pinus massoniana plantation]

To explore the effects of different disturbance patterns on restoring the health of an infected stand, concentrated disturbance of not cutting trees before 10 years after infection, mode-rate disturbance of cutting infected pine trees, and strong distrubance of cutting infected pine trees, the neighboring trees and poorly growing pine trees were compared in a pure Pinus massomiana plantation infected by Bursaphelenchus xylophlius in Anji, Zhejiang, China. After 16 years, the importance values of P. massoniana in the three treatments were: concentrated disturbance > mode-rate disturbance > strong disturbance. However, the importance values of broad-leaved trees showed the opposite trend. Compared with the concentrated disturbance, the average DBH of P. massoniana in the moderate and strong disturbance treatments were 1.2 and 1.7 times higher, respectively, and those of broad-leaved species were 1.3 and 1.9 times higher, respectively. The average height of pine trees in the moderate and strong disturbance treatments increased 1.5 and 2.0 times, respectively, and those of broad-leaved species 1.2 and 1.8 times, respectively. The tree volume per hectare in moderate and strong disturbance treatments were 5.2 and 3.8 times that of concentrated disturbance treatment, respectively. In the moderate and strong disturbance treatments, the number of trees in each diameter class was greater than in the concentrated disturbance treatment. The stand diameter distribution in the multi-storied moderate and strong disturbance treatments followed an inverse J-shaped curve. The species richness and biodiversity were significantly higher in the mode-rate and strong disturbance treatments than in the concentrated disturbance treatment. The individual size inequality and structural complexity indices followed the order of moderate disturbance > strong disturbance > concentrated disturbance. Under moderate and strong disturbance treatments, the single-storied and evenly aged pure P. massoniana plantation became multi-storied and unevenly aged mixed stands. All the three disturbance patterns promoted the succession of broad-leaved trees, with the pace of succession in the order of strong disturbance > moderate disturbance > concentrated disturbance. In conclusion, moderate disturbance achieved better restoration. Thinning pure P. massoniana plantation could accelerate the succession of a mixed stand to enhance resistance against Bursaphelenchus xylophlius invasion.