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，易发生火灾的林地与稀树草原均面临因火抑制措施及后续火敏感树种入侵所引发的管理难题。在美国太平洋西北地区，盖氏栎（Quercus garryana）林与稀树草原在无火烧的情况下，正遭受本土针叶树花旗松（Pseudotsuga menziesii）的入侵威胁。
在美国加利福尼亚州红杉国家公园的鲍尔德山（Bald Hills）区域，研究人员已采用计划火烧与针叶树移除的手段对已受入侵的林地进行修复。本研究探讨了火敏感树种入侵与修复措施对林下植被的影响，共设置四类处理组：计划火烧组、计划火烧+针叶树移除组、针叶树移除组，以及未实施任何修复的入侵林（对照组）。
包含计划火烧的处理组拥有最高的本土物种丰富度，这两类处理组同时在样地与处理尺度上拥有最高的外来物种丰富度。仅实施针叶树移除而未进行计划火烧的林地，其物种丰富度与多样性介于火烧处理组与未受修复的入侵林地之间。与所有修复处理组相比，未受修复的入侵林的物种丰富度与多样性均有所降低。非度量多维标度（NMS）排序分析显示，针叶树胸高断面积、针叶树枯落物与细木质残体与较低的物种丰富度和多样性呈负相关，而海拔与枯草丛厚度则与较高的物种丰富度和多样性呈正相关。指示物种分析表明，多数本土与外来物种均与未受火敏感树种入侵的火烧林地相关联。
综合与应用。本研究结果表明，计划火烧与针叶树移除均对林下植物群落具有积极作用：可提升栎林的物种丰富度、多样性与植被盖度，并促使林下植物群落从森林关联物种向更偏向林地关联的物种转变。由于外来草本植物持续大量存在，残存盖氏栎林的修复工作仍面临诸多挑战。