Simulating the Impacts of Wind Damage on Stand Structure and Dynamics of Plantations: a Case Study of Long-Term Cryptomeria japonica Experimental Plots with Two Spacing Trials

摘要

Wind damage often causes unexpected risks and losses for forest managers. The impacts of catastrophic wind damage can lead to considerable disturbances in forest management plans. In this study, we analyzed the effects of wind damage on 2 long-term experimental plots of Japanese cedar (Cryptomeria japonica D. Don) with 2 spacing trials (CJ_(3000) with an original density of 3000 trees ha~(-1) and CJ_(5400) with an initial density of 5400 trees ha~(-1)) in 1944 (from Typhoon B 174; T_1)and 1955 (from Typhoon Iris; T_2). These 2 experimental plots are located next to each other in the Xitou area of central Taiwan and were established via 2-yr-old seedlings in 1929. The objective was to simulate the impact of typhoons on the stand structure in terms of the present and long-term dynamics. First, the 3-parameter Weibull probability density function was used to fit and compare the diameter at breast height (DBH) distribution before and after wind damage occurred. Second, under an assumption of a self-thinning slope, a switching regression was used to simulate the number of trees between the 2 plots over time. Interventions by typhoons in 4 scenarios were assumed: plots suffered T_1, plots suffered T_2, plots suffered both T1 and T_2, and simulated plots experienced no intervention. Results showed that (1) more trees with medium and smaller DBHs were removed than larger ones in both plots, (2) the 3-parameter Weibull probability density function effectively fitted and described the DBH-class structure of plots before and after the disturbance, with the patterns of DBH distribution after the interventions being more concentrated and similar to the consequences of low (or light) thinning, (3) the switching regression with dummy variables effectively estimated changes due to the typhoon intervention and reductions in the number of trees in the 2 plots, in particular, the number of trees in CJ_(3000) were higher than those in CJ_(5400) after 50 yr of age, and (4) the impact of wind damage could change the original density structure, which would lead to long-term changes in stand structure and stock.