The multi-trophic impact of ash dieback

人们越来越认识到，为了更好地了解生态系统动态响应全球变化的因素，需要进行多营养研究，但这种研究很少，大多数集中在特定的类群和单向生态相互作用。当代全球生态系统变化的主要因素之一是病原体和害虫在全球范围内的传播和发生频率的增加，对生物多样性、生态系统功能和生物圈碳平衡产生了影响。在欧洲森林中，最近最严重的问题是真菌病原体Fraxineus在欧洲白蜡树（Fraxinus excelsior）范围内的传播，导致高达90%的白蜡树死亡率（“白蜡树枯死”）。通常情况下，50% - 70%的白蜡树在感染后的五年内死亡，有证据表明，年轻的树木会比成熟的树木死得更快，使再生不太可能。白蜡树是一种具有重要生态意义的物种，由于其高度可降解的凋落物，白蜡树生长迅速，养分周转率高，由于其天然稀疏的树冠，白蜡树的地面植物群多样性高。由于这些原因，它还影响着关键的生态系统属性和过程，如地球化学循环、林地结构和生物多样性。2017年，在牛津标志性的生态观测站怀瑟姆森林（Wytham Woods）发现了灰顶枯病。灰是Wytham林冠的主要组成部分，因此该物种的减少将对林地的生态，动态和碳收支产生深远的影响。虽然灰枯梢对灰树本身的影响已受到关注，但迄今为止还没有研究探讨灰枯梢的后果如何通过森林生态系统的多个营养级级联。Wytham是唯一定位于跟踪疾病的全部生态后果。我们建议研究灰枯梢对生物地球化学循环，栖息地结构和捕食，空间异质性和连通性的多营养影响。这将通过协调和扩大现有的对植被、鸟类和哺乳动物的监测，并启动对土壤和垃圾生物以及小气候的新研究来实现。这种协调的努力超过四年，将导致一个新的多营养树病原体破坏森林的后果的理解，提供适用于管理和减轻树木枯死事件的生态后果的见解。这些目标将通过一系列调查和实验来实现，为此，我们将采用“模拟白蜡树枯死”的实验方法，在选定的地块上，通过白蜡树的环树皮，导致死亡率>80%。这些处理将使我们能够专注于枯死的长期影响（感染后10-20年），树木死亡过程将占主导地位，相比之下，早期（3-7年）阶段的灰枯死监测在未操作的地块，占主导地位的冠层损失，而不是死亡率。此外，我们将利用现有的基础设施，监测整个林地的灰枯梢病的多营养效应。我们建议应用一个独特的多营养和数据丰富的检查级联的后果，这样一个广泛的大规模死亡事件的一个关键树种，检查方面，从生物化学循环到栖息地结构和空间连接使用模型类群从微生物和无脊椎动物的哺乳动物和鸟类。我们打算，这一广泛的分析将提供一个模型的影响，在全球温带阔叶林地的大规模树木死亡事件的研究。

It is increasingly recognised that multitrophic studies are needed for better understanding of ecosystem dynamics in response to agents of global change, yet such studies are rare, with most focusing on specific taxa and one-way ecological interactions. One of the major agents of contemporary global change in ecosystems is the global spread and increased frequency of pathogens and pests, with consequences for biodiversity, ecosystem functioning and biosphere carbon balance. In European forests, the most acute recent concern is the spread of the fungal pathogen Hymenoscyphus fraxineus across the range of the European ash tree (Fraxinus excelsior), resulting in up to 90% ash mortality ("ash dieback"). Typically, between 50% - 70% of ash trees die within five years of becoming infected and evidence suggests that young trees will die faster than mature ones, making regeneration unlikely. Ash is an ecologically important species that is associated with fast growth and high nutrient turnover, due to its highly degradable litter, and a high diversity of ground flora due to its naturally sparse canopy. For these reasons it also influences key ecosystem attributes and processes such as biogeochemical cycling and woodland structure and biodiversity.In 2017 ash dieback was detected in Wytham Woods, Oxford's iconic ecological observatory. Ash is a major component of the canopy in Wytham and so the decline of this species will have profound impacts on the ecology, dynamics and carbon budget of the woodland. While the impacts of ash dieback on ash trees themselves have received attention, no studies to date have explored how the consequences of ash dieback cascade through multiple trophic levels of a forest ecosystem. Wytham is uniquely positioned to track the full ecological consequences of the disease.We propose to examine the multi-trophic impacts of ash dieback on biogeochemical cycling, habitat structure and predation, and spatial heterogeneity and connectivity. This will be achieved by coordinating and expanding existing monitoring of vegetation, birds and mammals, and initiating new studies of soil and litter organisms and microclimate. This coordinated effort over four years will result in a novel multi-trophic understanding of the consequences of forest disruption by tree pathogens, providing insights that are applicable to managing and mitigating the ecological consequences of tree dieback events. The aims will be met through a range of surveys and experiments for which we will adopt an experimental approach of "simulated ash dieback" which will lead to >80% mortality through ring-barking of ash trees in selected plots. These treatments will enable us to focus on the longer-term impacts of the dieback (10-20 years after infection), when tree mortality process will dominate, in contrast to the early (3-7 years) stages of ash dieback monitored in the unmanipulated plots, dominated by canopy loss rather than mortality. Additionally, we will take advantage of existing infrastructure and monitor the multi-trophic effect of ash dieback across the woodland. We propose to apply a uniquely multitrophic and data-rich examination of the cascading consequences of such an extensive mass-mortality event of a key tree species, examining aspects ranging from biochemical cycling to habitat structure and spatial connectivity using model taxa from microorganisms and invertebrates to mammals and birds. We intend that this extensive analysis will provide a model for studies of the impact of mass tree mortality events in temperate broadleaf woodlands worldwide.