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Why have there been so few acorns this Seed Gathering Season?

The Tree Council

October 15, 2021

Whilst out seed gathering this year, you may have noticed that acorns are hard to come by. And you’re not alone. Right across the country, we are seeing one of the lowest fall of acorns for roughly 7 years.

Why are there fewer acorns this year?

The quick answer is that last year was what is known as a ‘mast year’. A mast year occurs roughly once every 5-10 years, and is where a tree species such as oak drastically increase the number of acorns they produce. The oak trees put so much energy into this bumper crop of acorns that they leave themselves little energy to continue producing the following years. So, since last year was a mast year, this year our beloved oaks are recovering resulting in far fewer acorns for wildlife and nature-lovers to enjoy.

Why do oak trees do this?

We do not know for sure why oak trees do this. But one theory is that there is an evolutionary advantage to producing an unreliable number of acorns each year. If it were too reliable, the theory goes, surrounding wildlife populations like that of squirrels, deer and birds would adjust and learn to eat the entire yearly crop. Mast years stop this from happening. In these years, oak trees flood the ecosystem and produce too many acorns for local wildlife to consume, meaning more will have the chance to grow into saplings come spring. And in the several years that follow a mast year where we see far fewer acorns, like this one, the cut to the food supply helps to control these wildlife populations so that there are fewer animals to gobble up acorns when the mast year comes back around. Effectively, what we are seeing are oak trees trying to stop their acorns from being eaten.

This phenomenon also isn’t exclusive to oak trees. Other iconic species such as beech also employ it, theoretically for the same reason: to stop so many of their seeds from being eaten.

When will there be acorns again?

The recovery period normally lasts 1-2 years. So you might begin to see acorns in the autumn of 2022, and come autumn 2023 we are likely to see acorns littering green spaces in full swing again.

How will it affect the supply of oak trees from tree nurseries?

Adam Owen, Director of Moor Trees and partner in our Close the Gap programme, runs community tree nurseries across Dartmoor and South Devon, and he gave his perspective on the issue:

“The lack of acorns this year means that there may well be a supply shortage of native British Oak trees in 2023/24 from our tree nurseries. Normally it takes 2 years in a nursery for an acorn to become a 20-40cm tall tree suitable for woodland or hedgerow planting.

In the past two years, we’ve had a good haul of acorns and so this year and next we’re ok. To mitigate for the challenge ahead, we’re looking at different options including:

  • improved compost and feeding techniques to get next year’s acorns to grow to the desired size within one year
  • holding back some 2022/23 oaks by reducing feed /watering /retention in pots to slow growth (oak trees are very good at waiting for the right conditions to put on growth, so respond well to being ‘slowed down’)
  • seeking a method to store acorns for longer so we pause germination within the year they fall, so we have a ready supply of acorns in the event of another fallow year.

Fingers crossed, we’ll be able to continue our supply of oak trees to local landowners, along with the other 20 native broadleaved tree species we annually grow.”

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