In 2021, two successive UK winter storms - Arwen and Barra - caused significant damage to UK oak across the North East of England, changing the treescape forever.
High winds are likely to continue to hit the UK as our climate crisis continues.
PhD student Kate Halstead discusses her recent research into why Storm Arwen so severely damaged notable oak across the North East of England. And, what Newcastle University is doing to understand the causes of tree damage to inform forest management.
Contents:
What is the risk to native oak?
Why was Storm Arwen so destructive to trees?
How do we mitigate future storm damage to oak?
What is the risk to native oak?
There is mounting evidence that due to climate change, storm events are increasing in intensity and occurring in once unaffected regions, where trees have less resilience to extreme windspeeds [1].
Windstorms have the potential to cause severe damage and rapid tree mortality via windthrow, windsnap and crown damage (Fig. 1). Two native oak species (Quercus robur and Quercus petraea) form a substantial component of broadleaf woodland in Great Britain [2]. Within Europe, Britain and Ireland represent the north-western extent of oak distribution and are subsequently believed to contain many unique and valuable adaptive variants that merit conservation efforts [3]. England’s woodlands contain a greater number of ancient native oak than all other European countries combined, and the longevity of oak also provides a rich habitat for many associated species.
Figure 1 Differing scales of storm damage to oak: a) windthrow, b) windsnap, and c) crown damage.
Extreme storm events have been identified as a significant abiotic threat to the health of UK native oak, causing severe damage and uprooting [3]. During Arwen, oak suffered considerable losses, in particular to notable and veteran specimens- this is of concern given the species’ ecological, cultural and historical significance.
Similarly, native UK oak take roughly 300 years to reach maximum carbon sequestration rates (Matthews, 1989). Storm events causing immediate oak mortality and inhibiting optimal carbon storage are of major concern.
This highlights the need for continuing monitoring and conservation of oak to facilitate climate change mitigation efforts.
The 2021 winter storm season
Storm Arwen brought exceptionally strong winds to the UK overnight on the 26th to 27th November 2021. The UK Meteorological Office issued a rare red warning for wind, as the developing storm in the North Sea tracked south to the North East of the UK. The North East of England and eastern Scotland were the worst affected as the storm brought northerly winds, which were gusting widely at over 31 m/s. The highest gust speed of the storm was recorded at Brizlee Wood, Northumberland, at 44 m/s (98mph) [4]. Extensive damage was experienced by trees, thousands were felled across the north of the UK.
Less than two weeks after Arwen, the UK was subjected to another named storm, Barra. Storm Barra brought strong winds and heavy rain across the UK from the 7th to 8th December 2021. In exposed coastal locations, winds gusted between 31-36 m/s (69-80mph), with the highest gust speed recorded at Aberdaron, Gwynedd, at 39 m/s (87 mph) [4]. The storm also hampered efforts to clear up remaining storm damage from Arwen, which had only occurred just 11 days earlier.
Although Barra did bring severe weather conditions to the UK, it should be noted that Barra was not an exceptional winter storm, unlike its predecessor, Arwen.
Why was Storm Arwen so destructive to trees?
The UK is subjected to a windy climate (in contrast to continental Europe), caused by the frequent passing of North-Atlantic depressions over the British Isles [3]. Historically, UK oak has been subjected to damage by catastrophic windstorms, such as the ‘Great Storm of 1987’. The prevailing wind direction in the UK is from the south west, as the winds track across the Atlantic Ocean. Storm Arwen was unique, due to the strong prevailing north-easterly wind direction, and, as such, was a once-in-a-generation storm event (Fig. 2).
Figure 2 A 24-hour storm regime for Storm Arwen recorded at Redesdale Camp weather station, Northumberland. Each segment of the wind rose corresponds to one-hourly record of wind speeds ≥ 18 m/s (gale force winds) and maximum wind gusts ≥ 25 m/s (storm force winds) and their corresponding directionality.
Localised damage patterns
In the aftermath of the two storms, a census of storm damage to native UK oak was carried out across three sites in the North East:
- The Wallington Estate, Northumberland,
- Cockle Park Farm, Northumberland, and
- Gosforth Nature Reserve, Tyne and Wear.
A total of 79 storm-damaged oak were recorded across all three approximately 80 ha study sites. We utilised a ground-based laser scanner to model the 3D tree structure of oak following storm damage, to understand the causes of damage (Fig. 3). Arwen and Barra were attributed to 92.4% and 7.6% of recorded damage overall respectively. Our findings highlight a clear dose/response relationship, whereby storms of greater magnitude caused a greater scale of damage.
Figure 3 A 3D point cloud of storm damaged oak using a GeoSLAM ZEB Horizon LiDAR scanner.
Crown damage was the most documented damage type and was present in 59.5% of the 79 surveyed trees, followed by windsnap, 22.8%, and windthrow, 17.7%. Bark defects were the most frequently encountered point of pre-existing structural weakness, making up 48.3% of all reported defects in damaged trees, followed by weak forks, 40%, and prune wounds, 11.7%.
However, there were several marked differences between our findings and those documented in the aftermath of the ‘Great Storm of 1987’ (the most comparable UK storm to Arwen in terms of the scale of damage). Perhaps the most notable difference was that, across the sites surveyed, oak in an open parkland or hedgerow setting appeared less storm damaged, in terms of recorded severity. In addition, there was a high incidence of recorded windsnap following Arwen, when compared to the storm in 1987, where damage was predominately windthrow.
How do we mitigate future storm damage to oak?
We are currently in the process of developing a statistical wind risk model, which aims to identify ‘predictor variables’, those factors which are most likely to predispose oak to damage during storms.
Such factors include considering the health of the oak prior to the storms using satellite imagery and tree ring analysis, and their growing location in terms of topography and aspect.
An understanding of the extent to which prior woodland management, growing location, and poor tree health contribute to damage, provides a unique insight, and will inform future management of oak for stakeholders.
References
- Quine, C.P., Gardiner, B.A. & Moore, J. (2021) ‘Wind disturbance in forests: The process of wind created gaps, tree overturning, and stem breakage’, in Plant Disturbance Ecology. [Online]. Elsevier. pp. 117–184. https://doi.org/10.1016/B978-0-12-818813-2.00004-6
- Brown, N., Vanguelova, E., Parnell, S., Broadmeadow, S. & Denman, S. (2018) ‘Predisposition of forests to biotic disturbance: Predicting the distribution of Acute Oak Decline using environmental factors’, Forest Ecology and Management, 407pp. 145–154. https://doi.org/10.1016/j.foreco.2017.10.054
- Quine, C.P., Atkinson, N., Denman, S., Desprez-Loustau, M.-L., Jackson, R. & Kirby, K. (2019) Action Oak Knowledge Review: an assessment of the current evidence on oak health in the UK, identification of evidence gaps and prioritisation of research needs. Haslemere, UK: Action Oak. ISBN 978-1-5272-4193-0
- Met Office. (2023) ‘UK Storm Centre’. Available at: https://www.metoffice.gov.uk/weather/warnings-and-advice/uk-storm-centre/index (Accessed: 13 February 2023).
Find out more
To find out more get in touch with the team:
Kate Halstead- k.e.halstead2@newcastle.ac.uk
PhD researcher, School of Natural and Environmental Sciences, funded by the NERC One Planet DTP and Action Oak.
You might also like
- read the paper: Kate Halstead, Rachel Gaulton, Roy Sanderson, Andrew Suggitt, Christopher Quine, Localised damage patterns to oak during severe UK storms in winter 2021, Forest Ecology and Management, Volume 562, 2024, 121942, ISSN 0378-1127, https://doi.org/10.1016/j.foreco.2024.121942
- learn more about the authors: Kate Halstead, Dr Rachel Gaulton, Dr Roy Sanderson, Dr Andrew Suggitt and Professor Chris Quine
- find out more about our funding partner Action Oak
- explore our innovative Modelling, Evidence and Policy research and our School of Natural and Environmental Sciences
