Revealing the hidden impact of plant pests and pathogens.

Plant and soil ecologist Dr Ruth Mitchell studies how human activities – such as land use, grazing pressure and the introduction of non-native pests and pathogens – affect biodiversity above and below ground, and suggests ways to mitigate these impacts.

Cascading threats

Most recently, Ruth’s work has focused on how emerging pests and pathogens threaten not only native trees but also a host of linked species. One critical current challenge in Europe is ash dieback, a non-native fungus accidently introduced around 30 years ago from Asia. Ash dieback has spread across the continent and is now decimating UK ash populations.

Ruth explains, “Ash is one of our most common native trees … we almost took them for granted until this.” But the impact of the disease goes way beyond the trees themselves. Crucially, very little was known about the effect of losing so many ash trees on other biodiversity: on the species using ash for food, or for breeding, roosting or nesting in.

Working with James Hutton colleagues as well as partners at Forest Research, the RSPB and RBGE, Ruth compiled a dataset of species using ash trees in the UK. The total was an amazing 955 species – far more than anyone had realised. “Importantly,” she explains, “45 of these species will only use ash trees and a further 62 will rarely use other species.” This means that a decline in UK ash populations impacts dozens of interdependent plants, animals and fungi. “These cascading effects of tree diseases on biodiversity had not been studied in the UK until our work,” Ruth says.

Innovative solutions

Looking to solutions, Ruth’s team worked with woodland managers and policymakers to assess whether other tree species could replace ash in this ecological context. “Obviously for those species that only use ash, there isn’t much we can do,” she laments, “But many can switch to other trees.” So they compiled data on alternative species that each of the 955 ash-associated species was able to switch to, suggesting targeted replacements to support ash-associated biodiversity.

They produced case studies with woodland managers showing how habitats could be managed to conserve as much of this biodiversity as possible, and worked with policymakers to support these efforts. For instance, Ruth explains, “We had to re-evaluate the role of sycamore, a non-native species.” Previously, the presence of sycamore led to woodlands being classified as degraded. “However, our work showed that sycamore can support some of the same species as ash, and also provides many similar ecosystem functions.” This research has already been used by NatureScot, Natural England and Defra to develop responses to ash dieback and tree health.

Welly boots and binoculars

Growing up in the countryside with a keen interest in wildlife, Ruth originally aimed at a career in practical conservation. However, she recalls, “Then I realised that what I really enjoyed was understanding how species interact and how human activities impacted those interactions – i.e., that there was a subject called ecology!” She was stubbornly undeterred by an English teacher who claimed she wouldn’t get a job “wandering around in welly boots with binoculars”. “I wish that teacher could have seen me any time over the last 30 years while on fieldwork!” she laughs.

A lady in a blue t-shirt wearing glasses, a backpack and carrying binoculars stands in front of a wooded hillside with a blue sky beyond.

An RSPB-funded PhD studentship studying the impact of tree and shrub encroachment on Dorset heathlands was a great start, “Blending advancing scientific understanding with making research results practical and accessible for conservation on the ground – something I have continued to aim for throughout my career.” Following this, Ruth worked for the RSPB before moving to Scotland: first at the Institute for Terrestrial Ecology/Centre for Ecology and Hydrology in Banchory, Aberdeenshire, then the Macaulay Land Use Research Institute (which in 2011 merged with the Scottish Crop Research Institute to become the James Hutton Institute).

It’s in Scotland that Ruth says, “I really feel I’ve found my ecological niche. I’ve been fortunate to work with some great colleagues. One of the joys of working in ecology in Scotland is that it is a fairly small world, across academia, conservation and policy. It’s easy to talk directly both with researchers doing similar work, and with policymakers and practitioners who will make use of the results. I love it when my work helps us understand more about how the natural world functions, and also when it facilitates actions to conserve or restore biodiversity. I get so much satisfaction from seeing my work used by policymakers and practitioners.”

Urgent action

Ruth is clear about the urgent need for action to protect biodiversity. “Sometimes we don’t need more science, we need more on the ground resources and action,” she says. “We must keep biodiversity high on the policy agenda … It’s easy to ignore in the face of more ‘immediate’ crises like pandemics, war and food security. We need to raise awareness that protecting biodiverse and functioning ecosystems provides solutions to many of these problems, and to build public understanding of the implications of the biodiversity crisis.”

It certainly seems there will be plenty of demand for Ruth’s expertise. “There’s an increasing number of non-native plant pests and pathogens arriving in the UK, with implications for biodiversity.” And her philosophy for finding innovative solutions to these challenges is simple: “A mix of wonder, delight and curiosity in how the natural world functions, coupled with a willingness to try new approaches and methods.” Ruth certainly has both in spades.

Dr Ruth Mitchell heads the Biodiversity and Ecosystems Group at the James Hutton Institute, and leads the Biodiversity Topic for the Scottish Government Rural Affairs, Food and Environment Strategic Research Programme. Her work is supported by the Scottish Government, NatureScot, Natural England and Defra as well as grants from UKRI. Find out more here.

This post is part of a series showcasing Scotland’s innovative, high-impact research supporting biodiversity conservation, in partnership with Scottish Government and NatureScot. Read the rest of the series here.

Further reading

Mitchell, R.J., et al. 2014. Ash dieback in the UK: a review of the ecological and conservation implications and potential management options. Biological Conservation 175: 95—109.

Mitchell, R.J., et al. 2019. Collapsing foundations: The ecology of the British oak, implications of its decline and mitigation options. Biological Conservation 233: 316—327.

Mitchell, R.J., et al. 2021. Cumulative impact assessments of multiple host species loss from plant diseases show disproportionate reductions in associated biodiversity. Journal of Ecology 110(1): 221—231.

Mitchell, R.J., et al. 2021. Functional and ecosystem service differences between tree species: implications for tree species replacement. Trees 35: 307—317.

Mitchell, R.J., et al. 2021. Identifying substitute host tree species for epiphytes: The relative importance of tree size and species, bark and site characteristics. Applied Vegetation Science 24(2): e12569.