The Ash Bud Moth and Woodland Connectivity

Fragmentation of habitat plays a major role in the decline of species and, as ecological research seeks for more evidence of the changing conditions across a wider landscape, increasing problems from the spread of tree diseases are adding to these threats to survival. In some cases, there is an obvious, visible isolation of trees and woodlands but we must also consider the less apparent isolation of some of the small but vital species that rely on those trees. Some wild species are generalists and may be more able to adapt to changing habitat, but others are specialists that may find the loss of certain species more of a challenge where movements, connections and gene flow around the landscape is more likely to be compromised.

On top of that, tree disease is an important factor and, in the wake of the well-known Dutch Elm disease some decades ago, a new threat to one of our important woodland trees has emerged in the form of ash dieback. Ash trees across the UK are dying or showing signs of serious decline. The question is, how will this loss of ash trees affect the movements of other species that rely on them, in particular, those that are known as ‘ash obligates’?

To answer this question, PhD researcher Fiona Plenderleith from the University of Aberdeen has recently taken the long trip south to begin her PhD field work on this subject. Standing on high ground over a mixed Dartmoor woodland, she explained, “I will be looking for the emerging caterpillars of the Ash Bud Moth (Prays fraxinella) which is an ash obligate moth. I plan to collect samples of them and other moth larvae emerging from ash buds at the same time.” Research shows that other studies have “considered the impact of ash dieback directly on forest insect biodiversity but little is known about the long-term impact to species … as a result of losses in connectivity”.

Fiona explained that, “This project aims to predict the impact of ash dieback on the persistence of ash-associated invertebrates at a local and regional scale.” She has specific lines of enquiry to investigate how the tree disease may impact gene flow among the moths, indicating the consequences of ash dieback for habitat connectivity.

“After a few weeks here, I will travel to different regions of the UK, following the arrival of Spring across the country.” Starting in Devon, she has had the help of the Woodland Trust, Devon Wildlife Trust, Natural England and others to gain permission to collect samples from a number of sites in and around Dartmoor. As things turned out, it was unfortunate timing; Fiona arrived in Devon in the middle of an unpredictable cold spell that would delay the signs of spring and the emergence of tree leaves. With rapidly diminishing time to carry out her field work she set about finding some caterpillars but firstly had to find the trees. At Hisley Wood in the Bovey Valley she spent a few hours walking around to plot the most likely areas where ash trees stood, beginning to look for feeding signs and frass, the tiny clusters of caterpillar droppings.

The ash bud moth emerges at a similar time to other moths that also feed on ash, so they are difficult to identify for certain – especially when they are so small. But an additional list of moth species that also have a high dependency on ash as a food plant are going to be useful if they also become part of the sample.

Fiona’s photos demonstrating the caterpillars and their feeding signs

During Fiona’s stay in Devon she was looking for around 10 to 15 caterpillar samples from each of the selected sites. With the weather conditions against her, her admirable enthusiasm emerged above the lack of Springtime progress. She explained she has, “really connected with wildlife and developed a fascination for UK wildlife” and she sees herself working in the UK for the foreseeable future. “There is a lot we need to do to demonstrate the full interconnectivity between species and across our landscapes.” It is valuable research as she may also be able to use computer simulations to assess different scenarios of tree loss and explore mitigation options, a particularly useful outcome for woodland managers.

So, the trees in Devon are marked with GPS locations and Fiona will collect more caterpillars from Suffolk and Cumbria before returning in a few weeks with a set of small mobile moth traps to collect some moth samples at the adult stage. Keep an eye on this blog to see how she gets on.

by Matt Parkins

Fiona Plenderleith is based at the University of Aberdeen, School of Biological Sciences and the James Hutton Institute and her work is sponsored (in part) by the Woodland Trust.

You can find out more about tree pests and diseases on the Woodland Trust website

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