Abstract Background insect herbivory, i.e. the minor but chronic plant damage caused by insects, is usually considered ‘negligible’ for plants when compared with the severe defoliation associated with forest pest outbreaks. We experimentally tested the hypothesis that the impacts of background herbivory on tree growth and mortality accumulate over years, resulting in much larger effects than usually assumed. In boreal taiga forests near Arkhangelsk (Northern Russia), application of insecticide at 10-day intervals for four growth seasons (June–September of 2014–2017) decreased foliage losses to insects in our study species (early successional deciduous Betula pubescens and Populus tremula; late successional coniferous Picea abies and Pinus sylvestris) from 2.04–6.35% to 0.72–1.18%. The magnitude of the insecticide treatment effect on plant losses to defoliating insects varied considerably among the study species, with the highest effect observed in white birch and the lowest effects in the two late successional species. Across all tree species, insecticide treatment nearly doubled the increase in tree biomass relative to control plots, demonstrating that background insect herbivory has major negative impacts on tree growth and productivity. The insecticide-treated plots showed the largest increase in biomass in Norway spruce and the smallest increase in European aspen when compared to the control plots. The changes in birch growth following the release from insect herbivory were three times greater than the effects of the same level of simulated herbivory in an earlier experiment, thereby hinting at the importance of herbivore-specific elicitors in the growth suppression of trees damaged by insects. The mortality of late successional species in the treatment plots increased nearly three-fold, whereas the mortality of early successional species did not change relative to controls, suggesting an increase in competitiveness of the early successional trees released from herbivory. Thus, in agreement with an earlier modelling study, we conclude that minor herbivore damage, over the long term, substantially reduces biomass production in North European forest trees. Due to differential effects on coexisting tree species, this damage has a pronounced impact on plant competitiveness and affects both the productivity and the structure of boreal forests.

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通过对背景昆虫食草动物的四年抑制，欧洲北方森林树木的生物量产量翻了一番

摘要 背景昆虫食草，即由昆虫引起的轻微但慢性的植物损害，与与森林害虫爆发相关的严重落叶相比，通常被认为对植物来说“微不足道”。我们通过实验测试了这样一个假设，即背景食草对树木生长和死亡率的影响会随着时间的推移不断累积，从而产生比通常假设的更大的影响。在阿尔汉格尔斯克（俄罗斯北部）附近的北方针叶林中，在四个生长季节（2014 年 6 月至 2017 年 9 月）中每隔 10 天使用杀虫剂减少了我们研究物种（早期演替落叶桦；晚演替针叶冷杉和樟子松）从 2.04-6.35% 到 0.72-1.18%。杀虫剂处理对落叶昆虫植物损失的影响程度在研究物种之间差异很大，在白桦中观察到的效果最高，在两个晚期演替物种中观察到的效果最低。在所有树种中，相对于对照地块，杀虫剂处理使树木生物量的增加几乎翻了一番，这表明背景昆虫食草对树木的生长和生产力有重大的负面影响。与对照地块相比，经杀虫剂处理的地块显示，挪威云杉的生物量增幅最大，而欧洲白杨的增幅最小。从昆虫食草动物释放后桦木生长的变化是早期实验中相同水平的模拟食草动物的影响的三倍，从而暗示了草食动物特异性诱导物在抑制被昆虫破坏的树木的生长中的重要性。处理地块中晚期演替物种的死亡率增加了近三倍，而早期演替物种的死亡率相对于对照没有变化，表明从食草动物释放的早期演替树木的竞争力增加。因此，与较早的建模研究一致，我们得出结论，从长远来看，轻微的食草动物损害会大大降低北欧林木的生物量产量。由于对共存树种的不同影响，这种损害对植物竞争力具有显着影响，并影响北方森林的生产力和结构。处理地块中晚期演替物种的死亡率增加了近三倍，而早期演替物种的死亡率相对于对照没有变化，表明从食草动物释放的早期演替树木的竞争力增加。因此，与较早的建模研究一致，我们得出结论，从长远来看，轻微的食草动物损害会大大降低北欧林木的生物量产量。由于对共存树种的不同影响，这种损害对植物竞争力具有显着影响，并影响北方森林的生产力和结构。处理地块中晚期演替物种的死亡率增加了近三倍，而早期演替物种的死亡率相对于对照没有变化，表明从食草动物释放的早期演替树木的竞争力增加。因此，与较早的建模研究一致，我们得出结论，从长远来看，轻微的食草动物损害会大大降低北欧林木的生物量产量。由于对共存树种的不同影响，这种损害对植物竞争力具有显着影响，并影响北方森林的生产力和结构。表明从食草动物释放的早期演替树木的竞争力增加。因此，与较早的建模研究一致，我们得出结论，从长远来看，轻微的食草动物损害会大大降低北欧林木的生物量产量。由于对共存树种的不同影响，这种损害对植物竞争力具有显着影响，并影响北方森林的生产力和结构。表明从食草动物释放的早期演替树木的竞争力增加。因此，与较早的建模研究一致，我们得出结论，从长远来看，轻微的食草动物损害会大大降低北欧林木的生物量产量。由于对共存树种的不同影响，这种损害对植物竞争力具有显着影响，并影响北方森林的生产力和结构。