Abstract：
Extreme droughts are globally increasing in frequency and severity. Most research on drought in forests focuses on the response of trees, while less is known about the impacts of drought on forest understory species and how these effects are moderated by the local environment. We assessed the impacts of a 45-day experimental summer drought on the performance of six boreal forest understory plants, using a transplant experiment with rainout shelters replicated across 25 sites. We recorded growth, vitality and reproduction immediately, 2 months, and 1 year after the simulated drought, and examined how differences in ambient soil moisture and canopy cover among sites influenced the effects of drought on the performance of each species. Drought negatively affected the growth and/or vitality of all species, but the effects were stronger and more persistent in the bryophytes than in the vascular plants. The two species associated with older forests, the moss Hylocomiastrum umbratum and the orchid Goodyera repens, suffered larger effects than the more generalist species included in the experiment. The drought reduced reproductive output in the moss Hylocomium splendens in the next growing season, but increased reproduction in the graminoid Luzula pilosa. Higher ambient soil moisture reduced some negative effects of drought on vascular plants. Both denser canopy cover and higher soil moisture alleviated drought effects on bryophytes, likely through alleviating cellular damage. Our experiment shows that boreal understory species can be adversely affected by drought and that effects might be stronger for bryophytes and species associated with older forests. Our results indicate that the effects of drought can vary over small spatial scales and that forest landscapes can be actively managed to alleviate drought effects on boreal forest biodiversity. For example, by managing the tree canopy and protecting hydrological networks.
摘要：
极端干旱在全球范围内的频率和严重程度都在增加。大多数关于森林干旱的研究集中在树木的反应上，虽然人们对干旱对森林林下物种的影响以及当地环境如何调节这些影响知之甚少。我们评估了为期45天的实验性夏季干旱对六种北方森林林下植物表现的影响，使用在25个地点复制的rainout庇护所进行的移植实验。我们记录了增长，立即活力和繁殖，2个月,模拟干旱一年后，并研究了不同地点之间环境土壤水分和冠层覆盖的差异如何影响干旱对每种物种表现的影响。干旱对所有物种的生长和/或活力产生负面影响，但是苔藓植物的效果比维管植物的效果更强，更持久。这两个物种与古老的森林有关，苔藓Hyloneiastrumumbratum和兰花Goodyerarepens，比实验中包含的更多才多艺的物种遭受更大的影响。在下一个生长季节，干旱降低了苔藓的繁殖产量。但增加了黄原毛的繁殖。较高的环境土壤水分减少了干旱对维管植物的一些负面影响。更密集的冠层覆盖和更高的土壤水分都减轻了苔藓植物的干旱效应，可能是通过减轻细胞损伤。我们的实验表明，北方的林下物种可能会受到干旱的不利影响，对于苔藓植物和与较老森林相关的物种，这种影响可能会更强。我们的结果表明，干旱的影响可能在较小的空间尺度上有所不同，并且可以积极管理森林景观以减轻干旱对北方森林生物多样性的影响。例如,通过管理树冠和保护水文网络。
