Chair of Nature Conservation and Landscape Ecology, Faculty of Environment and Natural Resources, University of Freiburg, Tennenbacherstraße 4, 79106, Freiburg, Germany.
Ecological Networks, Technical University of Darmstadt, Schnittspahnstraße 3, 64287, Darmstadt, Germany.
Oecologia. 2021 May;196(1):289-301. doi: 10.1007/s00442-021-04921-y. Epub 2021 Apr 25.
Plant diversity affects multi-trophic communities, but in young regrowth forests, where forest insects are in the process of re-establishment, other biotic and also abiotic factors might be more important. We studied cavity-nesting bees, wasps and their natural enemies along an experimental tree diversity gradient in subtropical South-East China. We compared insect communities of experimental young forests with communities of established natural forests nearby the experiment and tested for direct and indirect effects of tree diversity, tree basal area (a proxy of tree biomass), canopy cover and microclimate on bee and wasp community composition, abundance and species richness. Finally, we tested if the trophic levels of bees, herbivore-hunting wasps, spider-hunting wasps and their natural enemies respond similarly. Forest bee and wasp community composition re-established towards communities of the natural forest with increasing tree biomass and canopy cover. These factors directly and indirectly, via microclimatic conditions, increased the abundance of bees, wasps and their natural enemies. While bee and wasp species richness increased with abundance and both were not related to tree diversity, abundance increased directly with canopy cover, mediated by tree biomass. Abundance of natural enemies increased with host (bee and wasp) abundance irrespective of their trophic position. In conclusion, although maximizing tree diversity is an important goal of reforestation and forest conservation, rapid closure of canopies is also important for re-establishing communities of forest bees, wasps and their natural enemies.
植物多样性会影响多营养层生物群落，但在幼龄再生林中，森林昆虫正在重新建立，其他生物和非生物因素可能更为重要。我们在中国东南亚热带的一个实验树木多样性梯度上研究了洞穴筑巢蜜蜂、黄蜂及其天敌。我们将实验中的年轻森林昆虫群落与实验附近已建立的天然森林的昆虫群落进行了比较，并测试了树木多样性、树木基面积（树木生物量的代理）、冠层覆盖和小气候对蜜蜂和黄蜂群落组成、丰度和物种丰富度的直接和间接影响。最后，我们测试了蜜蜂、捕食性黄蜂、蜘蛛捕食性黄蜂及其天敌的营养层是否会做出类似的反应。随着树木生物量和冠层覆盖的增加，森林蜜蜂和黄蜂群落的组成逐渐向天然森林的群落恢复。这些因素通过小气候条件直接和间接增加了蜜蜂、黄蜂及其天敌的丰度。而蜜蜂和黄蜂的物种丰富度与丰度呈正相关，与树木多样性无关，而丰度则直接与冠层覆盖度有关，这是通过树木生物量介导的。天敌的丰度与宿主（蜜蜂和黄蜂）的丰度有关，而与它们的营养位置无关。总之，尽管最大限度地提高树木多样性是造林和森林保护的一个重要目标，但树冠的迅速闭合对于重新建立森林蜜蜂、黄蜂及其天敌的群落也很重要。
