British forests still feel the impact of the 1976 drought
24 July 2013
British Ecological Society press release
The drought caused by the blazing summer of 1976 caused permanent changes to British forests that are still evident today, researchers part-funded by NERC have discovered.
The scientists found that in Lady Park Wood in the Wye Valley, the long, hot summer of 1976 selectively killed off the more drought-sensitive beech, permanently suppressing the growth of the surviving trees. This tipped the balance in favour of the more drought-tolerant oak. There are now more oak relative to beech than in 1976, and oak is more competitive and growing better.
Published today in the British Ecological Society's journal Functional Ecology, the study could help us make our forests more resilient to future climate change.
Most research into the impact of climate change on plants and animals focuses on the effect of gradual warming over long periods of time. But extreme events like droughts and floods are also becoming more frequent and more intense due to climate change. And while they can cause major damage to plants and animals, they are difficult to study because of their rarity.
Ecologists from the University of Stirling and the Joint Nature Conservation Committee decided to investigate how the great drought of 1976 affected our forests by looking at Lady Park Wood in the Wye Valley. Hugging the border of England and Wales near Symonds Yat, the 45-hectare National Nature Reserve is ideal for this kind of study because it is an unmanaged woodland which has been the subject of long-term ecological research since 1945.
Drawing on regular forest surveys going back almost 70 years, Professor Alistair Jump of the University of Stirling and his team looked at how relative abundance of beech and sessile oak changed between 1945 and 2010. They also examined tree ring data to discover how growth rates of the two species altered over the same period.
Professor Jump said, "We wanted to identify whether events that we consider extreme from a human point of view are extreme for the trees that also experienced them. To help us to predict the impacts of future extreme events, we wanted to see how long it took for beech trees to recover from extreme drought and to compare drought effects on beech with another, more drought tolerant species, namely sessile oak."
"The drought of 1976 - the most intense since records began - has led to long-term changes in forest structure to this day, more than 30 years after the event," he adds.
The results show that forests can respond suddenly and unpredictably to extreme drought.
"Our study shows that the beech trees could tolerate drought with little long-term impact until a threshold of drought severity was reached. At this point, the trees suffered a sudden and previously unpredictable reduction in growth, with a very slow recovery. For beech, even the healthiest trees have never fully recovered from this most severe historical drought: even decades later, their growth is still suppressed," says Jump.
The results also have important implications for commercial forestry, because forests made up of tree species with different drought tolerances are much more resilient to environmental change than a single species system.
Jump says, "In managed forests, this has particular implications for resource stability in the future, given that trees are a long-term crop and extreme events are set to increase in frequency and intensity as our climate changes. Where appropriate, forest managers could promote resilience to future extreme events through manipulating species mixes in planted forests.
"Given the long lifespan of the trees which form forests, actions taken now have consequences far into the future. We urgently need to know now how they might respond to the kinds of challenges that are predicted for the rest of the 21st century and beyond, so that we can plan effectively."
Professor Alistair Jump
University of Stirling
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1. Liam Cavin et al (2013) 'Extreme drought alters competitive dominance within and between tree species in a mixed forest stand', doi: 10.1111/1365-2435.12126, is published in Functional Ecology on 24 July 2013.
2. The study was partially funded through the ERA-Net BiodivERsA project Beech Forests for the Future by the UK Natural Environment Research Council (NERC, grant NE/G002118/1).
3. Functional Ecology is published by Wiley-Blackwell for the British Ecological Society. Contents lists are available on the Functional Ecology website.
4. The British Ecological Society is the oldest ecological society in the world. A learned society and registered charity, the BES supports ecological science through its five academic journals, other publications, events, grants and awards. Founded in 1913, the BES is celebrating its centenary this year with a series of special events across the UK designed to give everyone the chance to get involved in ecology.
Press release: 39/13
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