Forest and Rangeland Stewardship, Colorado State University, Fort Collins, CO, USA.
Idaho Department of Agriculture, Coeur d'Alene, ID, USA.
Sci Rep. 2020 Oct 2;10(1):16400. doi: 10.1038/s41598-020-73273-z.
Landscape-scale bark beetle outbreaks alter forest structure with direct and indirect effects on plants and animals in forest ecosystems. Using alpine spruce forest and a native bee community as a study system, we tested how tree mortality from bark beetles impacts bee foraging habitats and populations. Bees were collected across the growing season (early-, middle-, and late-season) for two years using passive trapping methods, and collections were used to analyze patterns in species abundances and diversity. Three important findings emerged: (1) forest stands that were post-outbreak had 62% higher floral density and 68% more floral species during peak bloom, respectively, than non-affected stands; (2) bee captures were highest early-season (June) and were not strongly affected by bark beetle outbreak; however, mean number of bee species and Shannon-Weiner diversity were significantly higher in post-outbreak stands and this effect was pronounced early in the growing season. Corresponding analysis of β-diversity indicated higher accumulation of bee biodiversity in post-outbreak stands and a turnover in the ratio of Bombus: Osmia; (3) bee captures were linked to variation in foraging habitat, but number of bee species and diversity were more strongly predicted by forest structure. Our results provide evidence of increased alpine bee biodiversity in post-outbreak stands and increased availability of floral resources. We conclude that large-scale disturbance from bark beetle outbreaks may drive shifts in pollinator community composition through cascading effects on floral resources, mediated via mortality of overstory trees.
林火尺度的甲虫爆发通过对森林生态系统中的植物和动物产生直接和间接的影响来改变森林结构。我们以高山云杉林和本地蜜蜂群落作为研究系统，检验了甲虫引起的树木死亡如何影响蜜蜂的觅食栖息地和种群。在两年的时间里，我们使用被动诱捕法在整个生长季节（早期、中期和晚期）收集蜜蜂，并利用收集结果来分析物种丰度和多样性模式。有三个重要发现：（1）与未受影响的林分相比，爆发后林分在盛花期的花朵密度分别高出 62%，花朵物种分别高出 68%；（2）蜜蜂的捕获量在早期（6 月）最高，且不太受甲虫爆发的影响；然而，在爆发后林分中，蜜蜂物种的平均数量和香农-威纳多样性显著更高，这种影响在生长季节早期更为明显。β多样性的对应分析表明，爆发后林分中的蜜蜂生物多样性积累更高，而熊蜂：壁蜂的比例发生了变化；（3）蜜蜂的捕获与觅食栖息地的变化有关，但蜜蜂物种的数量和多样性更多地受到森林结构的预测。我们的研究结果提供了证据表明，甲虫爆发后的林分中高山蜜蜂的生物多样性增加，并且花卉资源的可用性增加。我们得出结论，大规模的甲虫爆发干扰可能通过上层树木死亡对花卉资源产生级联效应，从而驱动传粉者群落组成的变化。
