Spruce budworm (SBW) outbreaks are a major disturbance in North American forests. In Quebec, Canada, the recent history of SBW outbreaks at the local scale is well-known. Studies at the Québec scale nonetheless remain rare despite the need to better understand the dynamics of SBW outbreaks at a larger scale. This study aimed to reconstruct the spatiotemporal dynamics of SBW outbreaks during the 20th century across the insect's range in southern Quebec. To this end, we sampled 83 stands throughout southern Quebec. These stands were selected according to their age and the presence of black, white, and red spruce. In fact, spruce, unlike balsam fir, survives the SBW outbreaks and can record them in these growth rings. In each stand, cores were taken from 20 spruce trees. The dendrochronological series of more than 1,600 trees were analyzed, and we identified, through the k-means grouping of stands, the spatial patterns of tree growth for the three previously documented 20th century SBW outbreaks. The outbreaks were not homogeneous across the distribution range of the insect. Two groups of stands showed early- (1905–1930) and late-century (1968–1988) outbreaks of high severity and a mid-century (1935–1965) outbreak of moderate severity. This pattern is explained mainly by the presence of the insect within the balsam fir–yellow birch and balsam fir–white birch bioclimatic domains, areas where outbreaks tend to be most severe because of the abundance of balsam fir, the main SBW host species. However, these two models differ in terms of the duration of outbreaks. A third, more northern, cluster of stands experienced lower severity outbreaks over the 20th century, a pattern explained by a lower proportion of balsam fir trees in these landscapes. Our study shows that, on the one hand, these three groups of stands are defined by outbreaks of specific duration (an outbreak period beginning when more than 20% of the trees are affected and ending when <20% of the trees are affected) and severity (in terms of percentage of affected trees), and on the other hand they are spatially distinct and subject to different climatic conditions.

中文翻译：

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加拿大东部 20 世纪云杉芽虫爆发的时空动态：三种不同的爆发严重程度模式

云杉 budworm (SBW) 爆发是北美森林的主要干扰。在加拿大魁北克省，当地规模的 SBW 近期爆发历史是众所周知的。尽管需要更好地了解更大规模的 SBW 爆发的动态，但魁北克规模的研究仍然很少见。本研究旨在重建 20 世纪魁北克南部昆虫分布范围内 SBW 爆发的时空动态。为此，我们对魁北克南部的 83 个林地进行了采样。这些林分是根据它们的年龄以及黑色、白色和红色云杉的存在情况选择的。事实上，与香脂冷杉不同，云杉能够在 SBW 爆发中幸存下来，并且可以在这些年轮中记录它们。在每个林分中，核取自 20 棵云杉树。对 1,600 多棵树木的树木年代学系列进行了分析，我们通过林分的 k 均值分组确定了先前记录的三个 20 世纪 SBW 爆发的树木生长的空间模式。在昆虫的分布范围内，爆发并不均匀。两组林分显示了早期（1905-1930）和世纪晚期（1968-1988）的高度严重的爆发和一个中等严重程度的世纪中期（1935-1965）爆发。这种模式主要是由于在香脂冷杉-黄桦和香脂冷杉-白桦生物气候域中存在昆虫，这些区域的爆发往往最严重，因为香脂冷杉是主要的 SBW 宿主物种。但是，这两种模型在爆发持续时间方面有所不同。第三个更靠北的林分群在 20 世纪爆发了较轻的疫情，这些景观中香脂冷杉树的比例较低可以解释这种模式。我们的研究表明，一方面，这三组林分是由特定持续时间的暴发定义的（暴发期从超过 20% 的树木受到影响时开始，到不到 20% 的树木受到影响时结束）和严重性（就受影响树木的百分比而言），另一方面，它们在空间上是不同的，并受不同气候条件的影响。