停止商业性采伐对大兴安岭森林结构与地上生物量的影响

采伐是北方森林最主要的人为干扰之一,过去高强度采伐导致森林植被组成单一化和均质化。为提高森林的生态功能和经济效益,国家先后于2000年实施"天然林资源保护工程"、2014年实施全面停止天然林商业性采伐。为评价这两种政策下不同的采伐干扰对森林的直接影响,以大兴安岭林区为研究对象,采用空间直观景观模型LANDIS PRO,模拟比较2000—2100年"天然林资源保护工程"、全面停止商业性采伐政策下森林树种组成、年龄结构及森林地上生物量的长期变化特征及其差异性。研究结果表明:1)模型初始化的林分密度、地上生物量与2000年野外调查数据相吻合(P0.01),模型模拟结果具有较高的可靠性;2)对比分类经营,全面停止商业性采伐的实施:增大了优势树种(落叶松与白桦)的树种组成比例,减小了保护树种(云杉与樟子松)的比例;对树种组成在中长期影响显著(P0.05),降低了树种组成结构的多样性;总体上增加了林分平均胸高断面积,减小了林分密度;3)模型模拟100年,全面停止商业性采伐下中幼龄林向成熟林过渡,改善森林年龄结构;4)与分类经营相比,整个模拟时期内全面停止商业性采伐增加森林地上生物量,提高森林恢复速率,有助于森林地上总生物量的恢复与累积。但保护树种(云杉与樟子松)森林地上生物量在一定程度上有所下降,不利于提高珍贵树种的丰度。对评估森林管理方案在森林资源恢复上的作用和有效实施森林生态系统管理有重要的参考意义。

Long-term effects of commercial harvest exclusion on forest structure and aboveground biomass in the Great Xing'an Mountains, China

Boreal forests retain larger carbon reserves than other biomes. The boreal forests of China are in the Great Xing''an Mountains region, which contains approximately 24%-31% of the total forest carbon storage in China, and thus plays an important role in maintaining the national carbon balance. Timber harvest is a major anthropogenic disturbance in boreal forests, affecting forest structure and aboveground forest biomass over the long term. High-intensity harvest has resulted in simplification and homogenization of forest structure and composition in the past. Therefore, the Natural Forest Conservation Policy and the Commercial Harvest Exclusion Policy were successively implemented in 2000 and 2014, respectively, to balance ecological restoration and timber supply. The objective of this study was to investigate long-term effects of Commercial Harvest Exclusion on the structure and biomass of a boreal forest landscape in northeastern China. To do this, we simulated the effects of Natural Forest Conservation and Commercial Harvest Exclusion on forest structure and biomass using a spatially explicit forest landscape model (LANDIS PRO).We initialized the model using forest inventory data (second and third tier data from 2000) and conducted simulations for the Great Xing''an Mountains from 2000 to 2100. Our results suggested that 1) density and basal area between the initialized modeling results and forest inventory data in 2000 were consistent (P<0.01), suggesting that the initialized model results could represent the real forest landscape, and harvest results adequately represented real harvest events. 2) Larch and birch were now dominant, whereas a low proportion of aspen and spruce was present. Compared to the Natural Forest Conservation scenario, the Commercial Harvest Exclusion reduced the diversity of tree species by raising the proportion of the dominant species (larch and birch) and reducing the proportion of protected rare species (pine and spruce). There was a significant effect on forest composition in the medium and long-term periods. Overall, basal area was higher and density was lower under the Commercial Harvest Exclusion scenario than those under the Natural Forest Conservation scenario. 3) Commercial Harvest Exclusion strongly decreased tree abundance in the early stage and increased their abundance in the late, old-growth stage. 4) Compared to the Natural Forest Conservation scenario, the simulated biomass and rate of forest regeneration increased under the Commercial Harvest Exclusion scenario across all simulation periods. Commercial Harvest Exclusion helped to increase overall forest biomass, but reduced the biomass of pine and spruce, two rare and economically important species, suggesting that greater intensity of sylvicultural treatments are needed. These results could help to develop a forest management policy for the region.