阔叶红松林森林资源可持续利用方案

Evaluation of a sustainable forest utilization program for broadleaved Korean pine mixed forests in the Changbai Mountain region of Northeast China

天保工程实施后,为了促进次生林向原始阔叶红松林恢复,不采红松只采伐阔叶树种的经营方式在长白山地区被广泛应用,部分林区陷入可采伐资源匮乏的困境。为了探究阔叶红松林森林资源可持续利用方案,针对红松(蓄积)比例不同的阔叶红松林次生林,利用林木材积生长方程与保留系数模型,模拟了预设经营方案下林分总蓄积量与可采蓄积量动态变化。研究结果表明,在禁止采伐红松的经营方式下,红松(蓄积)比例较高的次生林将无法达到森林资源可持续利用的目标,次生林的经营方案需要根据林分中红松(蓄积)比例不同而区别制定:对于红松蓄积低于40%的次生林,推荐不采伐红松、20%采伐强度、40a周期的经营方案;对于红松蓄积高于40%的次生林,推荐可以采伐红松、20%采伐强度、30a周期的经营方案。另外,可采蓄积量的恢复期比总蓄积量的恢复期更长,以可采蓄积恢复期作为评价指标,确定采伐周期,更有利于森林资源的可持续利用。

China＇s Natural Forest Conservation Program was launched in 1998. Since then, a harvesting model based on logging broadleaved species while retaining Pinus koraiensis has been widely applied in the Changbai Mountain region of Northeast China. The primary goal of this model is to promote the return of degraded secondary forests to primary broadleaved Korean pine mixed forests （BKFs）. However, because of differences in tree species composition among secondary forests, this harvest model has led to a decrease in timber resources in some parts of the region. In order to explore a sustainable utilization program for BKFs, we simulated the dynamics of total timber stocks under different harvest scenarios. We selected five secondary 1-hm2 BKF plots, which had been established in 2007 in the area administered by the Lushuihe Forestry Bureau. In these plots, Pinus koraiensis accounted for approximately 20%, 30%, 40%, 50%, or 60% of the gross volume. We divided each plot into 25 subplots, each measuring 20 m20 m. Within these plots, we identified and measured all free-standing trees with a diameter at breast height of ≥2 cm at 1.3 m above the ground. To simulate volume dynamics in the plots, we divided the tree species into three groups, namely, conifer trees, commercial broadleaved trees, and other trees. For each group, we applied volume growth equations and survival index equations to predict the volume dynamics of stands. In addition, we tested the validity of the harvesting model by using paired t-tests to analyze data obtained over a 10-year period from 10 permanent plots, ranging in area from 0.25 hm2 to 0.5 hm2. We calculated the gross volumes and the volumes available for harvesting of stands under a range of management programs, with harvest intensities of 20%, 30%, or 40% and cutting cycles of 10 years, 20 years, 30 years, or 40 years. In addition, we divided the programs into two groups： in the first group, harvesting of Pinus koraiensis was permitted, whereas in the second group, harvesting of Pinus koraiensis was prohibited. We verified the validity of the harvesting model （t=0.229, P=0.829）. The logging schemes that prohibited harvesting of Pinus koraiensis not only restricted the volume of available timber but also made restoration more difficult. Even under the lowest harvest intensity of 20%, the available timber volumes did not return to original levels after 40 years of restoration in secondary forests, where Pinus koraiensis comprised 〉40% of the total volume. Hence, to achieve sustainable utilization in secondary forests, the characteristics of tree composition should be considered when developing harvest schemes. For secondary forests in which Pinus koraiensis comprises 〉40% of the total volume, the harvest scheme should permit harvesting of Pinus koraiensis with a cutting intensity of 20% at 30-year intervals. In contrast, for secondary forests in which Pinus koraiensis comprises 〈 40% of the total volume, the harvest scheme should prohibit harvesting of this species, with a cutting intensity of 20% at 40-year intervals. We further showed that the period required for restoring the volume available for harvesting was longer than the period required for restoring the gross volume. Hence, evaluation of the logging cycle according to the period required for restoring the volume available for harvest will more efficiently promote sustainable forest utilization.