Data_Sheet_1_Spread and Severity of Ash Dieback in Switzerland – Tree Characteristics and Landscape Features Explain Varying Mortality Probability.DOCX

Since the 1990s the invasive fungus Hymenoscyphus fraxineus has been threatening European ash (Fraxinus excelsior), a tree species with high ecological and economic importance. This pathogen is causing severe crown dieback, leading to high mortality rates across Europe and is present in Switzerland since 2008. In this study, we provide a comprehensive overview of the temporal evolution of crown damage and mortality rates in Switzerland over the 2009–2019 period. Harnessing the power of the annualized design of the Swiss national forest inventory (NFI), we show that annual mortality rates (AMRs) of ash increased significantly since the arrival of the fungus, with stronger effects in small trees [<26 cm diameter at breast height (DBH)]. Mortality modeling confirmed a size and growth-rate dependent mortality probability (MP). It also revealed that stands with higher humidity – either through higher mean annual precipitation or more humid soil conditions – showed also increased MP. Decreasing host abundance with increasing elevation was also associated with lower MP. Special ash surveys performed over the last 10 years still show a large percentage of ash trees with very low defoliation. This gives hope to finding possible tolerant or resistant trees for (inter-)national breeding programs. In the mean-time our results reinforce previously published management guidelines to promote not only healthy big trees, but also healthy and fast-growing young trees in more open stands for long-term conservation of ash in Europe.

自20世纪90年代以来，入侵性真菌蜡楝茎点霉（Hymenoscyphus fraxineus）一直威胁着欧洲白蜡树（Fraxinus excelsior）——这一兼具极高生态与经济价值的乔木树种。该病原菌可引发严重的树冠枯梢病，在欧洲全境造成极高林木死亡率，并于2008年传入瑞士。本研究全面梳理了2009至2019年间瑞士境内欧洲白蜡树的树冠损伤与死亡率随时间的演变趋势。依托瑞士国家森林清查（National Forest Inventory, NFI）的年度化调查设计，本研究证实：自该真菌入侵以来，白蜡树的年死亡率（Annual Mortality Rates, AMRs）显著升高，且对胸径（diameter at breast height, DBH）<26厘米的小径木影响更为显著。死亡率建模验证了死亡率概率（Mortality Probability, MP）与树木尺寸及生长速率的相关性；研究同时发现，林分湿度更高的样地——无论源于更高的年平均降水量，还是更湿润的土壤条件——其林木的死亡率概率也会上升。寄主丰度随海拔升高而降低的现象，同样与更低的死亡率概率相关。过去十年间开展的专项白蜡树调查仍显示，仍有大量白蜡树的落叶程度极低，这为在国家级乃至跨国育种计划中筛选潜在的耐受或抗病植株带来了希望。与此同时，本研究结果进一步支撑了此前发布的经营管理指南：为实现欧洲白蜡树的长期保育，不仅应培育健康的大径木，还应在更开阔的林分中促进健康且速生的幼木生长。