Forest insect outbreaks cause large changes in ecosystem structure, composition, and function. Humans often respond to insect outbreaks by conducting salvage logging, which can amplify the immediate effects, but it is unclear whether logging will result in lasting differences in forest structure and dynamics when compared with forests affected only by insect outbreaks. We used 15 years of data from an experimental removal of Tsuga canadensis (L.) Carr. (Eastern hemlock), a foundation tree species within eastern North American forests, and contrasted the rate, magnitude, and persistence of response trajectories between girdling (emulating mortality from insect outbreak) and timber harvest treatments. Girdling and logging were equally likely to lead to large changes in forest structure and dynamics, but logging resulted in faster rates of change. Understory light increases and community composition changes were larger and more rapid in the logged plots. Tree seedling and understory vegetation abundance increased more in the girdled plots; this likely occurred because seedlings grew rapidly into the sapling- and tree-size classes after logging and quickly shaded out plants on the forest floor. Downed deadwood pools increased more after logging but standing deadwood pools increased dramatically after girdling. Understory light levels remained elevated for a longer time after girdling. Perhaps because the window of opportunity for understory species to establish was longer in the girdled plots, total species richness increased more in the girdled than logged plots. Despite the potential for greater diversity in the girdled plots, Betula lenta L. (black birch) was the most abundant tree species recruited into the sapling- and tree-size classes in both the girdled and logged plots and is poised to dominate the new forest canopy. The largest difference between the girdling and logging treatments—deadwood structure and quantity—will persist and continue to bolster aboveground carbon storage and structural and habitat diversity in the girdled plots. Human responses to insect outbreaks hasten forest reorganization and remove structural resources that may further alter forest response to ongoing climate stress and future disturbances.

中文翻译：

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伐木响应改变了基础树种丧失后的重组轨迹

森林昆虫爆发导致生态系统结构、组成和功能发生巨大变化。人类通常通过抢救性采伐来应对昆虫爆发，这可以放大直接影响，但与仅受昆虫爆发影响的森林相比，尚不清楚采伐是否会导致森林结构和动态的持久差异。我们使用了 15 年的加拿大铁杉实验清除数据。 （东部铁杉）是北美东部森林中的基础树种，并对比了环剥（模拟昆虫爆发造成的死亡率）和木材采伐处理之间的反应轨迹的速率、幅度和持久性。环割和伐木同样可能导致森林结构和动态发生巨大变化，但伐木导致变化速度更快。在记录的地块中，林下光照增加和群落组成变化更大、更快。环带地块的树苗和林下植被丰度增加较多；发生这种情况的原因可能是，伐木后幼苗迅速长成幼树和乔木大小，并迅速遮蔽了森林地面上的植物。伐木后倒下的枯木池增加更多，但环割后直立的枯木池急剧增加。环割后林下光照水平在较长时间内保持较高水平。也许是因为环带地块中林下物种建立的机会窗口较长，环带地块的总物种丰富度比伐木地块增加得更多。尽管环围地块有可能实现更大的多样性，但黑桦树是环围地块和伐木地块中树苗和乔木大小类别中最丰富的树种，并且有望在新森林中占据主导地位天篷。环割和伐木处理之间的最大差异（死木结构和数量）将持续存在，并继续增强环割地块的地上碳储存以及结构和栖息地多样性。人类对昆虫爆发的反应加速了森林重组并消除了结构性资源，这可能进一步改变森林对持续气候压力和未来干扰的反应。