The multi-trophic impact of ash dieback

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.

This project will deliver impact to a range of stakeholders

1. Academic researchers interested in an integrated understanding of ecosystems, and in the whole ecosystem consequences of mass tree mortality. The work in this project provides a rare opportunity to develop a detailed multitrophic understanding of the functioning of a complex ecosystem, and of how that functioning is distorted by by ash dieback. Such an understanding would be of broad interest to ecologists and ecosystem scientists beyond the specifics of ash dieback, while also providing an ecologically rounded understanding of how ash dieback will affect woodland ecology and function.

2. The general public interested in woodland ecology, the complex connections within ecosystems and the consequences of ash dieback. This will in particular be delivered through a custom exhibition in the Museum of Natural History at Oxford. The Museum has a dedicated Wytham Room which features a range of exhibitions around ongoing research at Wytham. This museum has over 670,000 visitors a year, including over 35,000 schoolchildren on organised visits, and provides an outstanding forum with which to engage with the public and communicate our science. Many aspects of our research (forest disturbance, loss of an iconic tree species, three dimensional laser scanning, multitrophic interactions across plants, microbes, vertebrates and invertebrates) have inherent accessibility and potential to engage the public. We will develop a custom exhibition for the museum highlighting the full spectrum of our research, and engaging with museum staff, local artists and volunteers in its construction). We anticipate that at least 200,000 people would see this exhibition over a year. As part of this exhibition we will also develop some custom films describing the multitrophic ecology of Wytham Woods and the spread and impacts of ash dieback that will also be made available through the Oxford University Web Site.

3. Members of the wider scientific community and public interested in the data sets and research
As part of our strong philosophical commitment to free, fairly rapid and unrestricted availability of our field data for use by the wider community, the data collected by this project will be made freely available through Oxford University's newly constructed Wytham database, subject to fair use agreements that protect the ability of primary data collectors (especially students) to publish their data This task will be a key part of the job description of the assigned PDRA, using the databasing tools that we have already developed and engaging with student casual labour to facilitate the process. A copy of the data will also be deposited in the NERC Environmental Information Data Centre (see Outline Data Management Plan).

4. Policymakers and stakeholders
Understanding the complex ecological impacts of ash dieback are of inherent interest to policy makers and stakeholders. The direct impacts of ash dieback are expected to cost the UK £15 billion (Hill et al 2019), but these figures do not take into account many possible multitrophic feedbacks and interactions (which may be detrimental or beneficial). We will convene two policy stakeholder workshops in London, one at the start of the project to identify what sorts of output from this project would be most useful for shaping, and one towards the end of the project that would discuss the major findings of this project. Key stakeholders would include government departments (including DEFRA), agencies such as Natural England and the Forestry Commission, and NGOs such as the Woodland Trust. Meetings would be held either at the Royal Society, or at a Westminster venue if possible.