What factors influence the extent of midstorey development in Mountain Ash forests?

The midstorey is a critical component of the structure of many kinds of forest globally. We constructed statistical models of the factors influencing the percentage cover of two dominant Acacia spp. (Montane Wattle [Acacia frigiscens]) and Silver Wattle [Acacia dealbata]) in the midstorey of Mountain Ash (Eucalyptus regnans) forests in mainland south-eastern Australia. We modelled the influence on the percentage cover of two these two species of Acacia of : (1) the age of the overstorey eucalypts (which corresponded to the time elapsed since the last major stand-replacing disturbance), and (2) environmental drivers (slope, aspect, elevation, and topographic wetness). Stand age was an important factor influencing the percentage cover of both Montane Wattle and Silver Wattle. We found evidence of a non-linear, humped-shaped percentage cover-stand age relationship for the percentage cover of Montane Wattle, with the highest values in stands of Mountain Ash that were 30-60 years old. The...林中层（midstorey）是全球多数森林群落结构的关键组成部分。我们针对澳大利亚东南部大陆区域的巨桉（Mountain Ash，Eucalyptus regnans）林林中层，构建了两种优势金合欢属（Acacia spp.）物种盖度百分比的影响因子统计模型，这两个物种分别为山地金合欢（Montane Wattle，Acacia frigiscens）与银叶金合欢（Silver Wattle，Acacia dealbata）。我们针对这两种金合欢属物种的盖度百分比，建模分析了两类影响因素：(1) 上层桉树的林龄（即末次大规模林分更替干扰发生后的间隔时长）；(2) 环境驱动因子，涵盖坡度、坡向、海拔与地形湿度指数。林龄是影响山地金合欢与银叶金合欢盖度百分比的重要因素。研究结果显示，山地金合欢的盖度百分比与林龄呈非线性驼峰型相关关系，在树龄30~60年的巨桉林分中，其盖度达到峰值。