Why nature’s gone nuts for acorns!

It happens rarely. But this year our woodlands are inundated with them – and the reason is one of the wonders of the natural world

WITH golden leaves crunching underfoot and the rustle of birds and animals searching the undergrowth for food to add to winter stores, this is a rewarding time of year to be out in the British countryside.

But, as many people report bumper crops of acorns on this year’s oak trees, the pressing question for nature-lovers is this: will 2017 be a mast year?

The word ‘mast’ is used for the fruit of oak, beech, chestnut and other woodland trees. and for reasons scientists still don’t fully understand, our oaks do not produce uniform numbers of nuts each year.

sometimes there are next to none, in others only meagre crops. But at irregular intervals about every five to ten years, almost all oaks across the country join in a co-ordinated acorn boom.

In a mast year, far more acorns fall than wildlife can possibly consume. This gives the trees a better chance of creating oak saplings the following spring. It’s Mother Nature’s way of rigging the odds.

We already know that in the appalachian mountains of the United states, oaks are enjoying what looks like an epic mast year. But oak species vary around the world, as, of course, does the climate. It is too early to say for certain that Britain can look forward to a similar rich harvest, though the signs are good.

The last British mast was in 2013, so we may well be due for one.

Dr kate Lewthwaite, at the Woodland Trust, advises caution though, as its collectors’ data is not yet complete: ‘Many of them prefer using pen and paper and don’t like to send in their figures by email.’

Her team always likes to hear from the public, so this is a marvellous excuse for families to go out and collect valuable data.

To find oaks, don’t just look for the classic lone tree standing in a field. Oaks are common in hedgerows too, and in woodland, where, because they live much longer than all other trees (except the yew), they dominate. Oaks

can live for a millennium. according to an old saying, they take 300 years to grow, 300 years to stand still and 300 years to die. Their peak acorn-producing years are between the ages of about 40 and 150. It’s a long retirement.

This longevity affects their shape. Oaks can have a massive girth at the base, spreading out like an elephant’s foot to take all the extra weight of centuries.

They are also easy to spot because of their distinctive leaves and, of course, their acorns.

Defining what constitutes an exceptional crop is not an exact science. It’s all down to memory, familiarity and common sense.

The Woodland Trust asks volunteers to make an assessment by eye and produce a numerical grade: 1= no fruit, 2= meagre, 3= moderate, 4= good crop, 5= exceptional crop.

Dr Lewthwaite says: ‘The differences can be quite subtle. Most years score between 2 and 3. In 2013 the scores got close to 4.’

Though no one is sure how the trees work together, scientists generally agree that the most likely cause of mast years is ‘predator satiation’.

acorns and beechnuts are vital food sources for animals and birds including mice, deer, jays, wild boar and squirrels. It is possible the trees are, in effect, holding back food from these ravenous hordes, keeping their populations low before deluging them with more nuts than they can possibly eat, so as to ensure more acorns survive to become saplings.

after a mast year, there is often a population explosion of quick-breeding animals such as mice.

Just yesterday there were reports that this year’s bountiful supply of acorns could increase the incidence of tick- spread Lyme disease. Mice harbour this, and the more mice that survive the winter, the more ticks they infect in the spring — and those ticks can go on to bite humans. Up to 3,000 people a year are now infected with the disease.

some animals don’t just eat the trees’ nuts but help them to spread and propagate.

The squirrel (greys in particular) bustles around the forest floor at this time of year, scoffing as many acorns as it can and storing what it doesn’t immediately need in a collection of larders. squirrels have an extraordinary memory for where they stored acorns, but inevitably some will be left or not needed, and eventually take root.

an even more prolific acorn-gatherer is the jay. This colourful member of the crow family stores about three acorns (sometimes more) in its gullet and one in its beak, then hides them under leaves, in cracks in tree bark and in any other handy cubbyhole.

an adult jay can collect up to 5,000 acorns in a season and despite its formidable retrieval instincts, many of those will grow into oak trees. Not all animals are so helpful. Wild boar roamed Britain’s woods until the last one was killed in the 17th century. Now escapees from farms have made a return to some southern woods and are guzzling acorns and beechnuts.

since saxon times there has been a tradition of ‘pannage’, letting pigs loose in the forest so they can feast on acorns and beechnuts. This still happens each year in the New Forest in Hampshire.

AHappy side-effect of the tradition is it prevents the New Forest ponies poisoning themselves by eating too many acorns. The pigs are impervious to the acorns’ toxicity.

Trees expend a great amount of energy producing nuts for a mast year. They couldn’t do this every year without risking disease or stunting their growth. Experts say you can tell which years were mast years by examining the trunk of a felled tree to see where the rings are closest together — a sign all the tree’s energy went into its fruit that year.

It wouldn’t be wise for trees to over-supply acorn feeders continually. a voracious deer herd, for example, can strip a forest bare, not just gorging on nuts but eating bark, which can kill the tree. so the trees must co- operate, withholding nuts for years before simultaneously coming into fruit.

so how do trees of the same species growing hundreds of miles apart come to have the same mast years? It must, scientists believe, be related to temperature or rainfall in the spring.

The right combination of warmth, wind and moisture should produce the perfect conditions for the beech or oak trees’ flowers to bloom and their pollen to spread (although a late frost may ruin it all).

yet a string of what appear to be identical springs can produce just one that is magically followed by an unexpected mast autumn.

It is a puzzle but Dr Lewthwaite says: ‘I like mysteries in nature, and trees have had millions of years to evolve. I’m sure they know what they’re doing.’