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.

大型古树是全球森林生态系统中至关重要的关键种结构（keystone structures）。当前诸多森林生态系统中，这类古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变化的因素显得尤为关键。大型古树常分布于易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面积如何影响大型古树的倒伏风险仍缺乏充分认知。本研究基于维多利亚州中部高地山灰桉（Eucalyptus regnans）林分长达18年的定位观测，量化了样地内大型具树洞古树的倒伏概率与周边景观内采伐面积、火烧面积之间的关联关系。研究结果显示，周边景观内采伐林分面积越大，古树倒伏概率越高；周边火烧面积越大，倒伏概率同样升高，这一现象在腐朽程度极高的古树中尤为显著。周边采伐或火烧面积增加导致古树倒伏风险升高，最合理的解释是采伐迹地或火烧迹地会改变区域风动模式。既往研究已证实，本研究区域内的大型具树洞古树本就处于较高的倒伏风险之中；本次新增的分析结果进一步表明，周边景观开展额外采伐作业将进一步推高这一风险。现行采伐规程要求在采伐迹地内对大型具树洞古树进行保护。我们建议，若要降低未采伐样地内大型具树洞古树的倒伏概率，需开展精细化的景观规划，以限制周边区域的木材采伐量。