抚育间伐对蒙古栎次生林生长的影响

Abstract

Forest management strategies for natural secondary forests require appropriate thinning methods that are stable,efficient,and sustainable. In the present study,we investigated the influence of thinning intensity on tree growth and forest structure. We established three different thinning regimes( light,medium,and heavy) and a no-thinning( control)treatment in young( 15 years old) and middle-aged( 35 years old) Mongolian oak( Quercus mongolica) secondary forests in Liaoning Baishilazi National Nature Reserve. Data were collected 8 years and 26 years after thinning. In the young forest,we found that light,medium,and heavy thinning significantly influenced the average diameter at breast height( DBH) of the stand and its periodical increment. After 8 years,the average stand DBHs in the light,medium,and heavy thinning plots were 2.1 cm,1.3 cm,and 2 cm larger,respectively,than that in control plot. On the contrary,thinning intensity had no significant influence on stand volume growth. After 8 years,the total increments of stand volume in trees showing anincrease in DBH of 12 cm after the light,medium,and heavy thinning treatments were 0. 97,1. 03,and 1. 21 times higher,respectively,than those of control trees. The control stand and stands subjected to each thinning treatment exhibited a left single-peak mountain shape,implying that most trees were classified in the small DBH class. In the middle-aged forest,we found that thinning significantly influenced not only the average stand DBH but also the stand volume growth and its total increment. An increase in the thinning intensity resulted in a greater increase in the average stand DBH. In addition,heavy thinning significantly influenced the periodical increment of the average stand DBH. After 26 years,the average stand DBHs in the light,medium,and heavy thinning plots were 0. 3 cm,1. 7 cm,and 5. 1 cm greater,respectively,than that of control plot. After 26 years,the total increments of stand volume in trees showing an increase in DBH of 12 cm after the light,medium,and heavy thinning treatments were 1. 97,1. 65,and 1. 63 times higher,respectively,than that of control trees. Stands subjected to the light and heavy thinning treatments exhibited a right singlepeak mountain shape,implying that most trees were classified in the large DBH class and therefore the forest structure was considered to be optimal. On the contrary,the control stand and the stand subjected to the medium thinning treatment exhibited a left single-peak mountain shape,implying that most trees were classified in the small DBH class. The results of our comprehensive analysis of the impacts of age class and thinning intensity on forest growth suggest that the most effective forest management strategy for Mongolian oak secondary forests is to conduct light,medium,and heavy thinning in young forests,but only heavy thinning in middle-aged forests. However,to achieve an increase in total volume growth,the stand density should be ≥1600 trees per hectare.