Data from: Empirical relationships between tree fall and landscape-level amounts of logging and fire

Large old trees are critically important keystone structures in forest ecosystems globally. Populations of these trees are also in rapid decline in many forest ecosystems, making it important to quantify the factors that influence their dynamics at different spatial scales. Large old trees often occur in forest landscapes also subject to fire and logging. However, the effects on the risk of collapse of large old trees of the amount of logging and fire in the surrounding landscape are not well understood. Using an 18-year study in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria, we quantify relationships between the probability of collapse of large old hollow-bearing trees at a site and the amount of logging and the amount of fire in the surrounding landscape. We found the probability of collapse increased with an increasing amount of logged forest in the surrounding landscape. It also increased with a greater amount of burned area in the surrounding landscape, particularly for trees in highly advanced stages of decay. The most likely explanation for elevated tree fall with an increasing amount of logged or burned areas in the surrounding landscape is change in wind movement patterns associated with cutblocks or burned areas. Previous studies show that large old hollow-bearing trees are already at high risk of collapse in our study area. New analyses presented here indicate that additional logging operations in the surrounding landscape will further elevate that risk. Current logging prescriptions require the protection of large old hollow-bearing trees on cutblocks. We suggest that efforts to reduce the probability of collapse of large old hollow-bearing trees on unlogged sites will demand careful landscape planning to limit the amount of timber harvesting in the surrounding landscape.全球森林生态系统中，老龄大树是至关重要的关键枢纽结构。当前诸多森林生态系统内，这类大树的种群正快速衰退，因此量化不同空间尺度下影响其动态的因素具有重要意义。老龄大树常分布于同时受火灾与采伐干扰的森林景观中，但目前学界对周边景观内的采伐与火烧程度如何影响老龄大树倒伏风险的认知仍较为匮乏。本研究依托维多利亚州中部高地山灰桉（Eucalyptus regnans）林区开展的18年长期定位研究，量化了样地内具树洞的老龄大树倒伏概率与周边景观采伐程度、火烧程度之间的关联。 研究结果显示，周边景观内的采伐森林面积越大，大树倒伏概率越高；周边火烧面积越大，倒伏概率同样升高，这一现象在处于高度腐朽阶段的个体中尤为显著。周边采伐或火烧面积增加导致大树倒伏风险上升的最合理解释，是采伐迹地或火烧迹地会改变与之相关的局地气流运动模式。 已有研究表明，本研究区域内的具树洞老龄大树本就面临较高的倒伏风险。本文新增的分析结果进一步显示，在周边景观开展额外采伐作业将进一步推高这一风险。现行采伐规程要求对采伐迹地上的具树洞老龄大树实施保护。我们建议，若要降低未采伐样地内具树洞老龄大树的倒伏概率，需开展精细化的景观规划，以限制周边景观内的木材采伐规模。