Data from: Prescribed fire and conifer removal promote positive understory vegetation responses in oak woodlands

Fire-prone woodlands and savannas worldwide face management challenges resulting from fire exclusion and subsequent encroachment of fire-sensitive trees. In the Pacific Northwest (USA), Quercus garryana oak woodlands and savannas are threatened by encroachment from the native conifer Pseudotsuga menziesii in the absence of fire. In the Bald Hills of Redwood National Park (California, USA), prescribed fire and conifer removal have been used to restore encroached woodlands. We examined the effects of encroachment and restoration on understorey vegetation, comparing four treatments: prescribed fire, prescribed fire and conifer removal, conifer removal, and encroached (control). Treatments including prescribed fire had the greatest native species richness. These two treatments also had the greatest non-native species richness, both at the site and treatment level. Woodlands treated with conifer removal and no prescribed fire were intermediate in species richness and diversity compared to burned treatments and encroached woodlands. Encroached woodlands had diminished richness and diversity compared to all restoration treatments. Non-metric multidimensional scaling (NMS) ordination demonstrated that conifer basal area, conifer litter, and fine wood were associated with low species richness and diversity, and that elevation and thatch were associated with higher species richness and diversity. Indicator species analysis identified that most native species and non-native species were associated with burned woodlands that were never encroached. Synthesis and applications. Our results suggest that both prescribed fire and conifer removal have benefits for understorey plant communities, increasing species richness, diversity, and cover in oak woodlands, and shifting understorey communities from forest-associated species to more woodland-associated species. Restoration of remnant Quercus garryana oak woodlands is complicated by the persistence and abundance of non-native herbaceous plants.全球范围内，受火干扰频发的林地与稀树草原均面临由禁火措施及后续火敏感树种侵入扩殖所引发的经营管理难题。在美国太平洋西北地区，加里栎（Quercus garryana）林地与稀树草原在缺乏林火干扰的情况下，正受到本土针叶树种花旗松（Pseudotsuga menziesii）的侵入威胁。 在美国加利福尼亚州红杉国家公园的鲍尔希尔斯区域，研究人员已通过计划烧除（prescribed fire）与针叶树移除技术对受侵林地开展生态修复。本研究探讨了林火侵入与修复措施对林下植被的影响，共设置四组处理：计划烧除组、计划烧除联合针叶树移除组、针叶树移除组，以及未施加干预的受侵对照组。 包含计划烧除的处理组拥有最高的本土物种丰富度；该两类处理组同时在样地与处理尺度上均呈现出最高的外来物种丰富度。仅实施针叶树移除而未进行计划烧除的林地，其物种丰富度与多样性均介于火烧处理组与受侵对照林地之间。相较于所有修复处理组，受侵对照林地的物种丰富度与多样性均显著降低。非度量多维标度（Non-metric multidimensional scaling, NMS）排序分析结果表明，针叶树胸高断面积、针叶枯落物与细木质残体与较低的物种丰富度和多样性显著相关；而海拔与地表枯落物层则与较高的物种丰富度和多样性相关。指示物种分析结果显示，绝大多数本土物种与外来物种均与未受侵入的火烧修复林地显著关联。 研究总结与应用启示：本研究结果显示，计划烧除与针叶树移除均对林下植物群落具有积极效益，可提升栎类林地的物种丰富度、多样性与植被盖度，并推动林下植物群落由森林伴生物种向更适配林地生境的物种转变。由于外来草本植物持续存在且种群数量丰富，残存加里栎林地的生态修复工作仍面临复杂挑战。