Abstract More frequent and severe disturbances increasingly open the forest canopy and initiate tree regeneration. Simultaneously, increasing weather extremes, such as drought and heat, are threatening species adapted to cool and moist climate. The magnitude of the microclimatic buffering capacity of forest canopies to mitigate hot and dry weather conditions and its disturbance-induced reduction remains poorly quantified. Also, the influence of disturbance legacies (e.g., deadwood) on forest microclimate is unresolved. In a unique manipulation experiment we investigated (i) the microclimatic buffering capacity of forest canopies in years with different climatic conditions; (ii) the impacts of spatial disturbance patterns on surface light and microclimate; and (iii) the effect of deadwood presence and type on microclimate. Treatments included two disturbance patterns (i.e., aggregated and distributed), four deadwood types (i.e., standing, downed, standing and downed, removed), and one untreated control (i.e., nine treatments in total), replicated at five sites dominated by European beech (Fagus sylvatica L.) in southeastern Germany. We measured forest floor light conditions and derived diurnal extremes and variation in temperature (T) and vapor pressure deficit (VPD) during four consecutive summer seasons (2016 – 2019). The buffering capacity of intact forest canopies was higher in warm and dry years. Surface light was significantly higher in spatially aggregated disturbance gaps compared to distributed disturbances of similar severity. An increase in surface light by 10 % relative to closed canopies elevated Tmax and VPDmax by 0.42°C and 0.04 kPa, respectively. Deadwood presence and type did not affect the forest microclimate significantly. Microclimatic buffering under forest canopies can dampen the effects of climate change. However, increasing canopy disturbances result in more light penetrating the canopy, reducing the microclimatic buffering capacity of forests. We conclude that forest management should foster microclimatic buffering in forests as one element of a multi-pronged strategy to counter climate change.

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干扰模式和枯木对欧洲山毛榉林小气候的影响

摘要 更频繁和更严重的干扰越来越多地打开森林冠层并引发树木再生。同时，越来越多的极端天气，如干旱和高温，正在威胁适应凉爽潮湿气候的物种。森林冠层缓解炎热和干燥天气条件的小气候缓冲能力及其干扰引起的减少的幅度仍然很难量化。此外，干扰遗留物（例如枯木）对森林小气候的影响尚未解决。在一项独特的操作实验中，我们调查了 (i) 不同气候条件下森林冠层的小气候缓冲能力；(ii) 空间扰动模式对地表光和小气候的影响；(iii) 枯木的存在和类型对小气候的影响。处理包括两种干扰模式（即聚集和分布）、四种枯木类型（即站立、倒下、站立和倒下、移除）和一种未经处理的对照（即总共九种处理），在欧洲占主导地位的五个地点重复德国东南部的山毛榉（Fagus sylvatica L.）。我们测量了森林地面光照条件，并得出了连续四个夏季（2016 年至 2019 年）的昼夜极端温度和温度 (T) 和蒸汽压不足 (VPD) 变化。温暖干旱年份完整森林冠层的缓冲能力较高。与类似严重程度的分布式干扰相比，空间聚集干扰间隙中的表面光明显更高。相对于封闭顶篷，表面光增加 10%，Tmax 和 VPDmax 分别提高了 0.42°C 和 0.04 kPa。枯木的存在和类型对森林小气候没有显着影响。森林冠层下的小气候缓冲可以抑制气候变化的影响。然而，增加的冠层干扰会导致更多的光穿透冠层，从而降低森林的小气候缓冲能力。我们得出结论，森林管理应促进森林中的小气候缓冲，作为应对气候变化的多管齐下战略的一个要素。