The multi-trophic impact of ash dieback

人们越来越认识到，需要进行多营养研究，以便更好地了解生态系统动态，以应对全球变化的影响，但这类研究很少，大多数集中在特定的类群和单向生态相互作用上。当代全球生态系统变化的主要原因之一是病原体和害虫的全球传播和频率增加，对生物多样性、生态系统功能和生物圈碳平衡造成影响。在欧洲森林中，最近最令人担忧的是真菌病原体Fraxineus在整个欧洲白蜡树(Fraxinus Excelsior)范围内的传播，导致高达90%的白蜡树死亡(“白蜡树枯萎”)。通常，50%-70%的白蜡树在感染后五年内死亡，有证据表明，幼树比成熟树死亡得更快，因此不太可能再生。白蜡树是一种重要的生态物种，由于其高度可降解的凋落物而具有快速生长和较高的养分周转，而由于其天然稀疏的树冠而具有高度的地面植物多样性。出于这些原因，它还影响到关键的生态系统属性和过程，如生物地球化学循环和林地结构和生物多样性。2017年，在牛津标志性的生态天文台威瑟姆森林发现了白蜡树枯萎病。白蜡树是威瑟姆林冠的主要组成部分，因此白蜡树的减少将对林地的生态、动态和碳收支产生深远的影响。虽然白蜡树枯萎对白蜡树本身的影响已经受到关注，但到目前为止还没有研究探讨白蜡树枯萎的后果如何通过森林生态系统的多个营养水平级联作用。我们建议研究白蜡树枯萎病对生物地球化学循环、栖息地结构和捕食以及空间异质性和连通性的多重营养影响。这将通过协调和扩大对植被、鸟类和哺乳动物的现有监测，并启动对土壤、凋落物生物体和小气候的新研究来实现。这项为期四年的协调努力将导致对树木病原体破坏森林的后果的新的多营养理解，提供适用于管理和减轻树木枯萎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“模拟白蜡树枯萎”的实验方法，在选定的地块，通过对白蜡树进行环剥，将导致80%的死亡率。这些处理将使我们能够将重点放在枯萎的较长期影响上(感染后10-20年)，那时树木死亡过程将占主导地位，而不是在未经处理的地块中监测的白蜡树枯萎的早期阶段(3-7年)，以树冠损失为主，而不是死亡。此外，我们将利用现有的基础设施，监测整个林地白蜡树枯萎的多重营养效应。我们建议应用一种独特的多营养和数据丰富的方法来检验这种关键树种大规模大规模死亡事件的级联后果，使用从微生物和无脊椎动物到哺乳动物和鸟类的模式分类群检查从生化循环到栖息地结构和空间连通性的方方面面。我们希望这一广泛的分析将为研究全球温带阔叶林中大量树木死亡事件的影响提供一个模型。

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.