Forest understories play a vital role in ecosystem functioning and the provision of ecosystem services. However, the extent to which environmental conditions drive dominant ecological strategies in forest understories at the continental scale remains understudied. Here, we used ~29 500 forest vegetation plots sampled across Europe and classified into 25 forest types to explore the relative role of macroclimate, soil pH and tree canopy cover in driving abundance-weighted patterns in the leaf economic spectrum (LES) and plant size spectrum (PSS) of forest understories (shrub and herb layers). We calculated LES using specific leaf area (SLA) and leaf dry matter content (LDMC) and PSS using plant height and seed mass of vascular plant species found in the understories. We found that forest understories had more conservative leaf economics in areas with more extreme mean annual temperatures (mainly Fennoscandia and the Mediterranean Basin), more extreme soil pH and under more open canopies. Warm and summer-dry regions around the Mediterranean Basin and areas of Atlantic Europe also had taller understories with heavier seeds than continental temperate or boreal areas. Understories of broadleaved deciduous forests, such as Fagus forests on non-acid soils, or ravine forests, more commonly hosted species with acquisitive leaf economics. In contrast, some coniferous forests, such as Pinus, Larix and Picea mire forests, or Pinus sylvestris light taiga and sclerophyllous forests, more commonly hosted species with conservative leaf economics. Our findings highlight the importance of macroclimate and soil factors in driving trait variation of understory communities at the continental scale and the mediator effect of canopy cover on these relationships. We also provide the first maps and analyses of LES and PSS of forest understories across Europe and give evidence that the understories of European forest types are differently positioned along major axes of trait variation.

中文翻译：

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欧洲森林林下植被的叶经济和植物大小光谱

林下林木在生态系统功能和生态系统服务提供方面发挥着至关重要的作用。然而，环境条件在多大程度上推动了大陆范围内林下林木的主要生态战略，这一点仍未得到充分研究。在这里，我们使用了大约 29 500 个在欧洲采样的森林植被地块，并将其分为 25 种森林类型，以探索大气候、土壤 pH 值和树冠覆盖率在驱动叶片经济谱 (LES) 和植物大小的丰度加权模式中的相对作用林下层（灌木和草本层）的光谱 (PSS)。我们使用比叶面积 (SLA) 和叶干物质含量 (LDMC) 计算 LES，并使用林下发现的维管植物物种的植物高度和种子质量计算 LES。我们发现，在年平均气温更极端（主要是芬诺斯坎迪亚和地中海盆地）、土壤 pH 值更极端和树冠更开放的地区，林下林下的叶子经济更为保守。地中海盆地周围温暖和夏季干燥的地区和大西洋欧洲地区也有比大陆温带或北方地区更高的林下层和更重的种子。阔叶落叶林的林下，如非酸性土壤上的山毛榉森林，或沟谷森林，更常见的寄宿物种具有贪婪的叶子经济。相比之下，一些针叶林，如松、落叶松和云杉的泥沼林，或樟子松轻针叶林和硬叶林，更常见的寄宿物种，具有保守的叶子经济。我们的研究结果强调了大气候和土壤因素在推动大陆尺度林下群落性状变化方面的重要性，以及冠层覆盖对这些关系的中介作用。我们还提供了欧洲森林林下林木 LES 和 PSS 的第一张地图和分析，并提供证据表明欧洲森林类型的林木在性状变异的主轴上的位置不同。