Centre d'Etude de la Forêt, Département des Sciences du Bois et de la Forêt, Pavilion Abitibi-Price, 2405 Rue de la Terrasse, Université Laval, Québec, QC G1V0A6 Canada.
Ecol Appl. 2011 Mar;21(2):439-51. doi: 10.1890/09-2100.1.
Understanding how large herbivores shape plant diversity patterns is an important challenge in community ecology, especially because many ungulate populations in the northern hemisphere have recently expanded. Because species within plant communities can exhibit strong interactions (e.g., competition, facilitation), selective foraging by large herbivores is likely not only to affect the abundance of palatable species, but also to induce cascading effects across entire plant communities. To investigate these possibilities, we first tested the effects of deer browsing and soil disturbance on herbaceous plant diversity patterns in boreal forest, using standard analyses of variance. Second, we evaluated direct and indirect effects of deer browsing and soil disturbance on the small-scale richness of herbaceous taxa using a multilevel path analysis approach. The first set of analyses showed that deer browsing and soil disturbance influenced herb richness. Path analyses revealed that deer browsing and soil disturbance influenced richness via complex chains of interactions, involving dominant (i.e., the most abundant) browsing-tolerant (DBT) taxa and white birch (Betula papyrifera), a species highly preferred by white-tailed deer (Odocoileus virginianus). We found no evidence that an increase of white birch in fenced quadrats was the direct cause of a decrease in herb richness. However, we found strong evidence that a higher abundance of DBT taxa (i.e., graminoids and Circium arvense), both in fenced and unfenced quadrats, increased herb layer richness. We propose an empirical model in which competitive interactions between white birch and DBT taxa regulate the strength of facilitative relationships between the abundance of DBT taxa and herb richness. In this model, deer browsing and the intensity of soil disturbance initiate a complex chain of cascading effects in boreal plant communities by controlling the abundance of white birch.
了解大型食草动物如何塑造植物多样性模式是群落生态学的一个重要挑战，特别是因为北半球许多有蹄类动物种群最近有所扩张。由于植物群落中的物种之间可能存在强烈的相互作用（例如，竞争、促进），大型食草动物的选择性觅食不仅可能影响可食用物种的丰度，还可能在整个植物群落中引发级联效应。为了研究这些可能性，我们首先使用方差分析标准检验了鹿类啃食和土壤干扰对北方森林草本植物多样性模式的影响。其次，我们使用多层次路径分析方法评估了鹿类啃食和土壤干扰对草本分类丰富度的直接和间接影响。第一组分析表明，鹿类啃食和土壤干扰影响了草本植物的丰富度。路径分析表明，鹿类啃食和土壤干扰通过涉及主要（即最丰富）的耐受啃食（DBT）物种和白桦（Betula papyrifera）的复杂相互作用链影响丰富度，白桦是白尾鹿（Odocoileus virginianus）高度偏好的物种。我们没有发现证据表明围栏样方中白桦的增加是草本植物丰富度减少的直接原因。然而，我们发现强有力的证据表明，在围栏和非围栏样方中，DBT 类群（即禾本科植物和刺儿菜）的丰度较高会增加草本植物层的丰富度。我们提出了一个经验模型，其中白桦和 DBT 类群之间的竞争相互作用通过控制白桦的丰度来调节 DBT 类群丰度与草本植物丰富度之间的促进关系的强度。在这个模型中，鹿类啃食和土壤干扰的强度通过控制白桦的丰度，启动了北方植物群落中复杂的级联效应链。
