Where are all the acorns?

15 November 2021 | Posted in Charlotte Owen , Plants
Where are all the acorns?
Acorns © Neil Fletcher

Charlotte Owen

WildCall Officer 

Have you noticed that the Oak trees have been a bit bare this autumn? We’ve seen hardly any acorns but there were plenty last year. What’s going on?

The acorn crop does naturally vary from year to year, most noticeably due to the phenomenon of ‘masting’. In a ‘mast year’ Oak trees produce a bumper crop, with up to 10,000 acorns per tree. This creates such a super-abundant food supply for Jays, Wood Mice, Grey Squirrels and other small mammals that they cannot possibly eat them all – a strategy known as ‘predator satiation.’ Producing such a glut of acorns pretty much guarantees that some will survive to put down roots as the next generation of Oak saplings. It’s a successful strategy but it does come at a cost. Tree growth is stunted in a mast year, since nearly all of the Oak’s resources are diverted to acorn production. As a result, far fewer acorns will be produced in subsequent years as the tree recovers from its mammoth reproductive effort. Interestingly, producing fewer acorns for several consecutive years may also benefit the tree by keeping mice and other acorn predators under control, limiting their numbers via short rations.

Jay with acorn
Alan Price

Last year was a mast year, so this year was always going to be lighter on acorns – but they are still scarcer than expected. This is because the number of acorns produced also depends on weather conditions experienced in spring, when Oak trees are in flower. Only pollinated flowers will turn into acorns and Oaks are wind-pollinated, so they really need a warm, dry spring to create the ideal conditions for a good acorn crop. A cold, wet spring with late frosts will have the opposite effect, so this year’s challenging spring conditions on top of last year’s mast have resulted in a shortage of acorns.

Mast years tend to occur every 5-10 years but they don’t necessarily happen on a regular basis and are difficult to predict, due to the huge number of underlying factors that can influence when they might occur. The really fascinating thing about mast years is the coordination: if it’s going to happen, then it will happen right across the UK and nearly every single Oak tree will produce a bumper crop in the same year. Other trees also experience mast years, most notably Beech, and major mast years can even be synchronised right across northern and western Europe.

Comments

  • Mac Poulton:

    18 Nov 2021 11:52:00

    And apple trees – our old Discovery tree was covered in blossom last Spring ready for a bumper crop, then the severe weather took most of it onto the lawn and the crop was barely sufficient to feed the caddis fly larvae and starlings!

  • Liz:

    18 Nov 2021 11:53:00

    Yet, weather conditions will never be the same across the whole of UK, let alone across NW Europe. Some other mechanism must also be at play. Fascinating.

  • Jacqui:

    18 Nov 2021 12:51:00

    Thank you for this great explanation, I have two Oaks in the garden and there’s not a single acorn in sight, we were concerned that the trees were poorly but knowing what’s going on has put our minds at rest.

  • Craig Dann:

    18 Nov 2021 13:37:00

    Great to know.. couldn’t find one this year..

  • Sue:

    18 Nov 2021 13:39:00

    Bizarrely in West Sussex my large oak produced a massive harvest of acorns this year, far more than in 2020. The jays and squirrels have had a wonderful time.

  • Graham:

    18 Nov 2021 15:14:00

    I have noticed earlier this autumn that quite a few of the acorns had “gone fuzzy” with some sort of flower type growth. Not all the acorns were affected on the same trees but it was evident that the ones that were are not going to be viable. No idea what the cause is and not seen it before.

  • Pamela Rowland:

    18 Nov 2021 15:39:00

    We have several oaks, not an acorn in sight !
    Last year we had so many they became dangerous to walk on and we had to sweep them up several times. This year we have lots of baby oak trees. So…you win some you lose some !!

  • Rosalie:

    18 Nov 2021 17:05:00

    Another member from West Sussex- where I live – has said they’ve a bumper acorn year. We haven’t. I’m hoping that the squirrels will – well – die off a bit! In our very small garden surrounded by oaks we still have at least one in sight at most times of day. Sadly. Stealing the bird food.

  • Jennifer Bromfield:

    18 Nov 2021 17:11:00

    I was vaguely aware of the term ‘mask year’ thank you so much for a clear explanation. This has not been a good year for crabapples either, I usually produce 20-30 jars of crabapple jelly, not so this year. What fruit there is is poor quality, either unripe or if the colour has gone red the fruit is mushy. Also most contain a maggot. On the bright side the birds are having a real feast.

  • Mike:

    18 Nov 2021 18:07:00

    Many thanks for the explanation. I was wondering why I hadn’t seen any acorns so far this year!

  • Nicola:

    18 Nov 2021 19:00:00

    Thank you! We live in a lane full of Oaks and have been wondering where the acorns are this year!

  • Helen:

    19 Nov 2021 05:06:00

    I can’t say I has noticed a lack of acorns but now thinking about it I haven’t seen any. Fascinating read, thank you

  • Kevin Hannavy:

    19 Nov 2021 11:32:00

    Super clear explanation. Mast years phenomenon epitomizes nature of scientific knowledge—-some aspects well understood but plenty still to be discovered. Any evidence that mycorrhizal networks are involved with coordination?

  • Sue McRae:

    19 Nov 2021 13:07:00

    I was aware of mast years for oak – and no, our 3 oaks had no acorns this year, but do horse chestnuts have a similar regime? I normally pick up at least a thousand but there was maybe only a hundred this year.

  • 20 Nov 2021 17:57:00

    I’m convinced it works mainly through mycorrhizal networks

  • Jan Bennett:

    23 Nov 2021 15:08:00

    Often see beautiful jays in my local cemetery, plus a green woodpecker. When recently bringing home the geraniums from our family graves, an acorn had landed in one. Have left it there to see what happens!

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