‘From little acorns mighty oaks grow’ - Why we should be worried for our native oak trees

Last autumn, under the canopies of native oak trees across the UK, the ground was a carpet of acorns. Each of these small, hard, cylindrical shaped nuts contains a seed of the parent tree. And so the old English saying goes, ‘from little acorns mighty oaks grow’.  

Our native Quercus species, the pedunculate or ‘English’ oak (Quercus robur) and sessile oak (Quercus petraea), have co-evolved with our native wildlife. It has been calculated that these oaks support over 2,300 other species, with 326 of them being entirely dependent on our native oaks for survival. Animals such as red squirrels and jays feast upon the energy rich acorn capsules and hoard some away for leaner times.  

A bumper crop of acorns is known as a mast year - when trees, such as oaks, synchronise high production of their fruits or nuts. Witnessing this phenomenon last autumn, people across the UK submitted acorn crop records to the Woodland Trust for their Nature’s Calendar project. It’s a long-running citizen science project that tracks signs of the changing seasons. With records going back to 1736, the Nature’s Calendar dataset is invaluable for studying the impact of weather and climate change on natural events.

Spotting the pattern of large acorn crops last year prompted me to write the BBC AutumnWatch blog: ‘What’s with all the acorns this year?’

Where have all the acorns gone?  

Scientists have identified a ‘boom and bust’ pattern in acorn production. In ‘boom’ years – like that of 2020 – oak trees produce more acorns than the animals which feast upon them can possibly eat. These are followed by ‘bust’ years, when acorn production is lower and trees instead focus on growth. Supporting this, Nature’s Calendar records so far this year show many people are finding very few acorns on their local, native oak trees. In fact the data we've had so far suggests the lowest crop of acorns in 20 years of Nature's Calendar records. 

So, should we be worried about our native oak trees? Yes, unfortunately so. 

Whilst the lack of acorns this autumn is in part due to a natural cycle, unfortunately our cherished oak trees are facing a myriad of threats. These are not only causing harm to individual trees but will also impact future generations of oak, if less acorns are produced.  

Weather and climate change 

In any given year acorn production is very much reliant on the weather. Nature’s Calendar records show oak trees usually flower from mid April to late May. 

Through April and into May this year we had some unusually late frosts, which can damage or even destroy oak flowers. Instead of the dry weather needed to aid pollination, the Met Office calculated that May had 171% of the average rainfall across the UK, making it the fourth wettest May since 1862. Following this we had a very dry summer, with each month from June to September having less than average rainfall. If a tree is suffering water stress, acorns may not develop and swell.  

It’s predicted that climate change will continue to result in more extreme weather events, as well as hotter, drier summers and this will have numerous negative impacts for our trees. Add your records to Nature’s Calendar and help us track the impacts of climate change. 

Acute oak decline 

As our climate changes and summers become drier, the resulting lack of water can cause oak trees to be more susceptible to acute oak decline. This is a disease which occurs when an individual trees are under strain, for example due to drought, waterlogging and high pollution levels. Whereas a healthy tree can withstand some pressures and fight off pests and disease, with acute oak decline the trees simply do that – they decline.  

An oak with acute decline may ‘bleed’ and its canopy will begin to dieback as the tree no longer has the energy needed for leaf production. The Woodland Trust’s tree health project, Observatree, has been tracking acute oak decline, which, at the moment, is mostly found in Wales and south of England. 

Records show that, where pressures are not alleviated, the oak tree can die within 5 years. With this pattern of weather predicted to continue with climate change, and without pressures such as high nitrogen levels being tackled, acute oak decline is only set to pose a bigger threat to our native oak trees.  

What does the future look like for our native oak trees? 

The symbol of strength. Epitomising endurance. A sign of fertility.  

Oak trees have been held in high esteem across cultures and religions for centuries, considered sacred and venerated by ancient kings, royalty and Roman commanders; their existence is wrapped up in history, folklore and legend.  

Many individual oaks are much loved and celebrated and are often given local names – something we do for few other plants: the Major Oak in Sherwood Forest was reputedly a safe haven for Robin Hood and his Merry Men, the Birnam Oak in Perth and Kinross is written about by William Shakespeare and Turner’s Oak at the Royal Botanic Gardens Kew was dubbed the ‘the tree that taught the world a lesson’. 

If we want future generations to revere oak trees in the way we have for so many centuries, we need to support our native oak trees.  

The oak leaf is also well recognised as the Woodland Trust’s symbol. I think it’s a very good choice. It’s the Woodland Trust’s 50th anniversary next year and I want it to continue being our symbol for another 50 years. And, in fact, 500 years after that, when some of the saplings we plant this autumn will be ‘middle-aged’, yet ancient oak trees.  

The Woodland Trust is the UK's largest woodland conservation charity. Our vision is a UK rich in native woods and trees, for people and wildlife. We create havens for wildlife by planting millions of trees every year, campaign for new laws to protect ancient woodland, restore damaged ancient woods, identify tree pests and diseases and track the impacts of climate change on our wildlife.  

Won’t you join us? Afterall, from little acorns mighty oaks grow and every action can make a mighty difference.  Find out more