Edge influence on vegetation at natural and anthropogenic edges of boreal forests in Canada and Fennoscandia

1. Although anthropogenic edges are an important consequence of timber harvesting, edges due to natural disturbances or landscape heterogeneity are also common. Forest edges have been well-studied in temperate and tropical forests, but less so in less productive, disturbance-adapted boreal forests. 2. We synthesized data on forest vegetation at edges of boreal forests and compared edge influence among edge types (fire, cut, lake/wetland; old vs. young), forest types (broadleaf vs. coniferous) and geographic regions. Our objectives were to quantify vegetation responses at edges of all types and to compare the strength and extent of edge influence among different types of edges and forests. 3. Research was conducted using the same general sampling design in Alberta, Ontario and Quebec in Canada, and in Sweden and Finland. We conducted a meta-analysis for a variety of response variables including forest structure, deadwood abundance, regeneration, understorey abundance and diversity, and nonvascular plant cover. We also determined the magnitude and distance of edge influence using randomization tests. 4. Some edge responses (lower tree basal area, tree canopy and bryophyte cover; more logs; higher regeneration) were significant overall across studies. Edge influence on ground vegetation in boreal forests was generally weak, not very extensive (distance of edge influence usually < 20 m) and decreased with time. We found more extensive edge influence at natural edges, at younger edges and in broadleaf forests. The comparison among regions revealed weaker edge influence in Fennoscandian forests. 5. Synthesis. Edges created by forest harvesting do not appear to have as strong, extensive or persistent influence on vegetation in boreal as in tropical or temperate forested ecosystems. We attribute this apparent resistance to shorter canopy heights, inherent heterogeneity in boreal forests and their adaptation to frequent natural disturbance. Nevertheless, notable differences between forest structure responses to natural (fire) and anthropogenic (cut) edges raise concerns about biodiversity implications of extensive creation of anthropogenic edges. By highlighting universal responses to edge influence in boreal forests that are significant irrespective of edge or forest type, and those which vary by edge type, we provide a context for the conservation of boreal forests.

1. 虽然人为边缘（anthropogenic edges）是木材采伐的重要后果，但由自然干扰或景观异质性形成的边缘也十分常见。学界已对温带与热带森林的林缘开展了充分研究，但对生产力较低、适应干扰的北方针叶林（boreal forests）的林缘研究则相对不足。2. 本研究整合了北方针叶林林缘的植被数据，并对比了不同边缘类型（火烧、采伐、湖泊/湿地边缘；幼龄与老龄边缘）、森林类型（阔叶与针叶林）以及地理区域间的边缘效应差异。本研究的目标是量化各类林缘的植被响应，并对比不同类型边缘与森林间边缘效应的强度与范围。3. 研究在加拿大阿尔伯塔省、安大略省、魁北克省以及瑞典和芬兰采用统一的通用采样方案开展。我们针对多种响应变量开展了荟萃分析，涵盖森林结构、枯木丰度、森林更新、林下植被丰度与多样性，以及非维管植物盖度。此外，我们还通过随机检验确定了边缘效应的幅度与影响距离。4. 整体来看，部分边缘响应（如较低的树木胸高断面积、林冠盖度与苔藓盖度；更多的枯木；更高的更新率）在所有研究中均表现显著。北方针叶林林缘对地表植被的影响通常较弱且范围有限（边缘效应影响距离通常小于20米），并随时间推移而减弱。我们发现，自然边缘、幼龄边缘以及阔叶林中的边缘效应范围更广。区域对比结果显示，芬诺斯坎迪亚地区森林的边缘效应相对更弱。5. 综合分析表明，与热带或温带森林生态系统相比，森林采伐形成的人为边缘对北方针叶林植被的影响并未表现出同等的强度、范围与持久性。我们将这一相对抗性归因于北方针叶林较矮的林冠高度、固有的景观异质性，以及其对频繁自然干扰的适应性。尽管如此，自然干扰（火烧）与人为活动（采伐）形成的边缘对森林结构的响应存在显著差异，这引发了人们对大规模人为边缘创建对生物多样性影响的担忧。本研究明确了北方针叶林林缘响应的共性——无论边缘或森林类型如何均表现显著，以及因边缘类型而异的响应特征，从而为北方针叶林的保护提供了理论依据。