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Seed Gathering Season: Acorns abound this autumn!

The Tree Council

October 7, 2022

Science and research
The number of acorns produced by the UK’s mighty native oaks appears to have increased significantly this autumn, following an almost total absence in 2021. This will come as a welcome relief for seed gatherers and wildlife alike.

The Tree Council celebrates Seed Gathering Season each autumn, but the number of acorns produced by an oak varies hugely year on year – with some years of extreme bounty – called ‘mast years’. The word ‘mast’ relates to the old English word ‘mæst’ – when acorns accumulated on the ground and were eaten by domestic animals like pigs. 2022 looks to be a really good acorn year.

Jon Stokes, Director of Science and Research from The Tree Council said “Our oak trees are an iconic feature of our countryside, but they are in fact two species: sessile oak (Quercus petraea) and pedunculate oak (Quercus robur). Despite being the most widely planted broadleaf tree in the UK, the supply of British acorns to tree nurseries is still limited. To be able to plan ahead and successfully collect more acorns at the right time, we need to better understand the biology of masting.”

Ryan McClory, a PhD candidate at the University of Reading, is focusing on the possible triggers for oak ‘masting’ in the UK – insight that is particularly useful for the conservation and tree growing industries. Ryan, whose PhD is part-funded by our friends at Action Oak, said: “2021 was a poor year for acorns seemingly across the whole of the UK, but in 2022, there has been a vast recovery in acorn numbers”

Similar to other tree species, oak trees flower each year, and yet only masts at irregular intervals, occasionally separated by several years. The acorns cannot be stored for long periods of time, increasing the importance of understanding, and harnessing the masting cycle for successful native oak regeneration.

Ryan said – “My acorn counts in Wytham Woods near Oxford were: 2020 = 4,787 acorns; 2021 = 1 acorn; 2022 = 2,828 acorns”

A mast year sees a tree species drastically increase the number of seeds it produces, such as acorns, but no-one is quite sure of the cause or the reason. The longest known study of acorn production we have in the UK is at Silwood Park in Berkshire, collected over 44 years by Professor Mick Crawley. His data shows that the average acorn crop fluctuates from year to year, often with low acorn years alternating with higher acorn years. He has also observed multiple poor years in a row, but what is rarer is two good years in a row. The factors that lead to this variability, are however still unclear.
Ryan believes mast years are influenced by three key factors: the weather; pollination efficiency and a tree’s ability to regenerate spent internal resources, and for oak ‘a dry and warm spring seems important, to allow for efficient flowering’. He suspects that ‘the warm, dry spring air caused all the oaks to flower at once aiding pollination – plus there was less rain to wash pollen out of the air.’

It can take over 40 years for oaks to produce acorns and they can suffer from poor natural regeneration in the UK as acorns are such an important food source for wildlife. The majority of new oak woodland in Britain is therefore established via planting which is why we need to encourage more acorn collection to set up local community tree nurseries.

Over at Moor Trees, a charity dedicated to restoring native woodland in Dartmoor and south Devon, Director Adam Owen has also observed the abundant return of acorns following 2021’s low count.
Adam said: “Last year, there were virtually no acorns around Dartmoor for Moor Trees to collect, so we are very pleased to see a good crop once again this year. We were concerned by the potential impacts of the drought, but it appears the oak trees, alongside other species, have produced ample seed.
Adam believes the summer drought “undoubtedly had an impact” on tree seed production, with many trees producing seed in numbers, but very early. He cited rowan as an example, where seeds would normally be collected in late September “but most rowan seed has now passed over and withered, if not eaten by birds”.

Jon said “Climate change will likely result in more and more extreme weather events, and whilst most oaks seem to have fared well and produced many healthy-looking acorns this autumn, the trees will also have suffered drought stress, with some acorns dropping early or dying on the branch. We have also noticed a surprising number of jet-black acorns on many oak trees, the biology of which is still unclear.”

You can play your part in growing the mighty oaks of the future, by collecting some acorns from your local trees this year and giving each seed the chance to become a tree benefitting many generations to come. You can find out more about how to grow trees from seed at www.treegrowersguide.org.uk from 17 October 2022.

Visit our Seed Gathering Season page for lots of useful resources and tips, and don’t forget to share your discoveries on social media using #GetGathering2022.

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