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.

This project examines the multi-trophic impacts of ash dieback on biogeochemical cycling, habitat structure and predation, and spatial heterogeneity and connectivity. This has been 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.

This project was funded by NERC under grant number NE/T007648/1 and rand ran March 2020 - March 2025