Studies on the role of geomorphology on vegetation structure at the basin scale are rarely available and less likely in the future due to access, funding, and potential health risks. Our goal is to determine the primary abiotic controlling factor(s) on shrub canopy structure using a dataset of approximately 23 million individual shrubs, generated using remote sensing and ground-truthing by Young et al. (in Remote Sens 9(5):16, https://doi.org/10.3390/rs9050458 , 2017). We posit that landscape position and local-scale geomorphic features in a desert alluvial fan environment will influence canopy volume and shrub spacing of creosote bush Larrea tridentata. We relate selected characteristics (canopy volume and spatial distribution) of identified L. tridentata to aspect and surface geomorphology at each shrub location. Statistical analyses included K-S testing, distribution fitting, and several generalized linear models (GLMs). The study was located in Eldorado Valley, Nevada, USA. Aspect and surface age have demonstrable influences on both shrub canopy volume and shrub spacing for all 5 geomorphic surfaces studied, with the highest median canopy volumes on east-facing surface (0.758 m3) almost 5 × larger than the lowest median volumes (0.152 m3) on the WNW-facing surfaces; variability in shrub volume was also higher on east-facing than west-facing surfaces. Shrub spacing on alluvial flat and fan skirt surfaces (2.418 and 2.333 m, respectively) were larger than older alluvial fan, fan piedmont and fan remnant surfaces (1.776, 1.837 and 1.892 m, respectively). Results show a significant relationship between shrub spacing and canopy volume by aspect and geomorphic surface, indicating a threshold at which biotic effects on canopy structure from intra-species competition transition to abiotic effects governed by geomorphic and climatological factors.

中文翻译：

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美国莫哈韦沙漠北部杂酚油灌木丛冠层体积和间距的地貌控制

由于获取、资金和潜在的健康风险，关于地貌对流域尺度植被结构作用的研究很少可用，而且在未来不太可能进行。我们的目标是使用约 2300 万株个体灌木的数据集确定灌木冠层结构的主要非生物控制因素，该数据集由 Young 等人使用遥感和地面实况生成。（在 Remote Sens 9(5):16，https://doi.org/10.3390/rs9050458，2017 年）。我们假设沙漠冲积扇环境中的景观位置和局部尺度地貌特征将影响杂酚油灌木 Larrea tridentata 的冠层体积和灌木间距。我们将已识别的三齿龙舌兰的选定特征（冠层体积和空间分布）与每个灌木位置的坡向和地表地貌联系起来。统计分析包括 KS 检验、分布拟合和几个广义线性模型 (GLM)。该研究位于美国内华达州的埃尔多拉多谷。坡向和地表年龄对所有 5 个地貌表面的灌木冠层体积和灌木间距都有明显的影响，朝东表面的最高中值冠层体积 (0.758 m3) 比最低中值体积 (0.152 m3) 大近 5 倍在面向 WNW 的表面上；朝东表面的灌木体积变异性也高于朝西表面。冲积平坦面和扇裙面的灌木间距（分别为 2.418 和 2.333 m）大于旧的冲积扇、扇前和扇残面（分别为 1.776、1.837 和 1.892 m）。