抚育间伐对蒙古栎次生林生长的影响

Effects of thinning on growth of Mongolian oak(Quercus mongolica)secondary forests

科学合理的抚育间伐措施是实现天然次生林稳定、高效、可持续经营的必然要求。以辽宁白石砬子国家级自然保护区萌生蒙古栎次生林为研究对象,设置幼龄林(15年生)和中龄林(35年生)两组抚育间伐试验区,利用两组试验区伐后8a和26a的长期连续测定数据,比较分析了不同抚育间伐强度对林分生长及结构的影响。结果表明,蒙古栎次生林幼龄林阶段经轻度、中度、强度间伐8a后,林分平均胸径及定期生长量与对照相比均有极显著差异,平均胸径分别比对照高2.1、1.3和2 cm;不同间伐强度对林分蓄积增长量影响不大,轻度、中度和强度间伐12 cm以上径阶蓄积定期生长量累计分别是对照的0.97、1.03和1.21倍。中龄林阶段,轻度、中度、强度间伐26a后林分平均胸径分别比对照高0.3、1.7和5.1 cm,强度间伐能显著提高林分平均胸径生长量;间伐能显著提高林分蓄积定期生长量累计及定期生长量,轻度、中度和强度间伐12 cm以上径阶蓄积定期生长量累计分别是对照的1.97、1.65和1.63倍;轻度、强度间伐林分胸径呈单峰右偏山状分布,大径阶树木占绝对优势,而中度间伐、对照林分胸径呈单峰左偏山状分布。综合分析不同林龄阶段不同强度抚育间伐措施对林分生长状况的影响,可以得出蒙古栎天然次生林高效经营技术为幼龄阶段时采用轻度、中度、强度间伐均可,在中龄林时宜采用强度间伐(保留密度1600株/hm2)。

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 an increase 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 single-peak 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.