The midstorey is a critical structural component of many forests globally. Using statistical models, we quantified the influence of two sets of variables on the percentage cover and basal area of two dominant Acacia spp. (Montane Wattle [Acacia frigescens] and Silver Wattle [Acacia dealbata]) in the midstorey of Mountain Ash (Eucalyptus regnans) forests in mainland south‐eastern Australia. Specifically, we focused on the influence of (1) the age of the overstorey eucalypts (corresponding to the time since the last stand‐replacing disturbance), and (2) environmental drivers (aspect, topographic wetness index, slope, elevation). We found evidence for generally non‐linear relationships between stand age and the percentage cover and the basal area of both Silver Wattle and Montane Wattle. Silver Wattle had the highest values for percentage cover, and Montane Wattle the lowest, in stands regenerating from fire in 2009. The basal area of Silver Wattle was highest in stands that regenerated after the 2009 wildfires and after disturbance that occurred between 1960 and 1990s. For Montane Wattle, basal area was lowest in stands that regenerated in 2009 but values did not differ among stands of other ages. Both Acacia species were a midstorey component in old‐growth Mountain Ash forest. No environmental covariates influenced the percentage cover of Montane Wattle or Silver Wattle. However, our model for the basal area of Montane Wattle contained evidence of a positive relationship with topographic wetness. The general paucity of environmental drivers in most of the models we constructed is likely due to the fact that both tree species occur well beyond our study region. Hence, the set of environmental conditions modelled may not be limiting the percentage cover or basal area of these midstorey tree species. Disturbance appears to be the key driver of dynamics of Montane Wattle and Silver Wattle in Mountain Ash forests.

中文翻译：

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哪些因素会影响山灰森林中层相思的发生和丰度？

中层是全球许多森林的重要结构组成部分。使用统计模型，我们量化了两组变量对两个优势相思树种的覆盖率和基础面积的影响。（山地荆[相思frigescens ]和银合欢[金合欢]）在山灰的midstorey（杏仁桉）澳大利亚东南部大陆的森林。具体来说，我们集中在以下方面的影响：（1）高层桉树的年龄（对应于自上次林木替换干扰以来的时间），以及（2）环境驱动因素（纵横比，地形湿度指数，坡度，海拔）。我们发现了林分年龄与银Wa和山Mont的百分比覆盖率和基础面积之间通常呈非线性关系的证据。在2009年从火中再生的林分中，Silver Wattle的覆盖率最高，而Montane Wattle最低。在2009年的野火和1960至1990年代之间发生干扰后再生的林分中，Silver Wattle的基础面积最高。对于Montane Wattle，在2009年更新的林分中，基础面积最低，但其他年龄林分的值没有差异。两个都相思树种是旧的山灰森林的中层成分。没有环境协变量影响Montane Wattle或Silver Wattle的百分比覆盖率。但是，我们的Montane Wattle基底面积模型包含与地形湿度呈正相关的证据。在我们构建的大多数模型中，环境驱动因素普遍缺乏，这可能是由于两种树种都发生在我们研究区域以外的事实。因此，建模的一组环境条件可能不会限制这些中层树种的覆盖率或基础面积。干扰似乎是山区灰森林中Montane Wattle和Silver Wattle动态变化的主要驱动力。