Forest Nature Conservation, Faculty of Forest Science and Ecology, University of Göttingen, Göttingen, Germany.
Bordeaux-Sciences-Agro, INRAE, UMR ISPA, Villenave d'Ornon, France.
Ecol Appl. 2023 Mar;33(2):e2786. doi: 10.1002/eap.2786. Epub 2023 Jan 8.
Recent ecological research suggests that, in general, mixtures are more resistant to insect herbivores and pathogens than monocultures. However, we know little about mixtures with non-native trees, where enemy release could lead to patterns that differ from commonly observed relationships among native species. This becomes particularly relevant when considering that adaptation strategies to climate change increasingly promote a larger share of non-native tree species, such as North American Douglas fir in Central Europe. We studied leaf damage on European beech (Fagus sylvatica) saplings and mature trees across a wide range of site conditions in monocultures and mixtures with phylogenetically distant conifers native Norway spruce (Picea abies) and non-native Douglas fir (Pseudotsuga menziesii). We analyzed leaf herbivory and pathogen damage in relation to tree diversity and composition effects, as well as effects of environmental factors and plant characteristics. We observed lower sapling herbivory and tree sucking damage on beech in non-native Douglas fir mixtures than in beech monocultures, probably due to a lower herbivore diversity on Douglas fir trees, and higher pathogen damage on beech saplings in Norway spruce than Douglas fir mixtures, possibly because of higher canopy openness. Our findings suggest that for low diversity gradients, tree diversity effects on leaf damage can strongly depend on tree species composition, in addition to modifications caused by feeding guild and tree ontogeny. Moreover, we found that nutrient capacity modulated the effects of tree diversity, composition, and environmental factors, with different responses in sites with low or high nutrient capacity. The existence of contrasting diversity effects based on tree species composition provides important information on our understanding of the relationships between tree diversity and plant-herbivore interactions in light of non-native tree species introductions. Especially with recent Norway spruce die-off, the planting of Douglas fir as replacement is likely to strongly increase in Central Europe. Our findings suggest that mixtures with Douglas fir could benefit the survival or growth rates of beech saplings and mature trees due to lower leaf damage, emphasizing the need to clearly identify and compare the potential benefits and ecological trade-offs of non-native tree species in forest management under ongoing environmental change.
最近的生态研究表明，一般来说，与单一种植相比，混交林更能抵御昆虫食草动物和病原体的侵害。然而，我们对非本地树木的混交林知之甚少，在这种混交林中，天敌的释放可能导致与常见的本地物种关系不同的模式。当考虑到适应气候变化的策略越来越多地促进更多的非本地树种，如中欧的北美花旗松时，这一点尤其重要。我们研究了在广泛的地点条件下，欧洲山毛榉（Fagus sylvatica）幼树和成熟树木的叶片损伤，这些地点条件包括单一种植和与远缘针叶树本地挪威云杉（Picea abies）和非本地花旗松（Pseudotsuga menziesii）的混交。我们分析了叶片食草动物和病原体损伤与树木多样性和组成效应的关系，以及环境因素和植物特征的效应。我们观察到，在非本地花旗松混交林中，山毛榉幼树的食草动物和树木吸吮伤害较低，而在山毛榉单一种植林中则较高，这可能是由于花旗松树上的食草动物多样性较低，以及在挪威云杉中比在花旗松混交林中的山毛榉幼树的病原体损伤较高，这可能是由于树冠开阔度较高。我们的研究结果表明，对于低多样性梯度，树木多样性对叶片损伤的影响除了受到取食群和树木个体发育的改变之外，还强烈依赖于树种组成。此外，我们发现养分能力调节了树木多样性、组成和环境因素的影响，在养分能力低或高的地点有不同的反应。基于树种组成的多样性效应的存在，为我们理解在非本地树种引入的情况下，树木多样性与植物-食草动物相互作用之间的关系提供了重要信息。特别是在最近的挪威云杉死亡之后，作为替代品种植花旗松在中欧很可能会大幅增加。我们的研究结果表明，由于叶片损伤较低，花旗松混交林可能有利于山毛榉幼树和成熟树木的存活或生长速度，这强调了在持续的环境变化下，森林管理中需要明确识别和比较非本地树种的潜在益处和生态权衡。
