With autumn in full swing it’s that time of year again when trees produce beautiful colours and then sadly start to lose their leaves. We have received a number of reports of early tinting of leaves this year, but have you noticed anything unusual about woodland trees' fruit?

What is a mast year?

Mast is the term used to describe the fruit of forest trees such as acorns and beech seeds. A mast year is when the trees that produce these fruits have a bumper crop and produce much more fruit than they normally would.

Trees such as oak and beech fluctuate massively year on year in the fruit they produce - in some years no fruit will be seen and in others, they have an exceptional crop.

Why do trees do this?

One of the major theories amongst scientists for this behaviour is predator satiation. Many animals including mammals and birds feed on this woodland fruit. The trees in effect holding back for a few years keeps these populations low. Then during a mast year, more food is produced than these frugivores can possibly eat, ensuring that some seeds will start to grow.

This has a major evolutionary advantage for the tree. Producing seeds is costly work so it's important that some of the fruit will grow. Producing fruit in a mast year does stunt growth of the tree but as this only occurs every five to ten years, it’s a worthy pay off to ensure the production of more saplings. 

How do trees do this?

Mast years are not just one off events occurring with one specific tree the vast majority of woodland trees across the UK will have a fantastic crop. So how do trees seemingly miles apart communicate with one another? This is one of nature’s mysteries, but it's probably to do with the weather. The right combination of temperature and rainfall in the spring is thought to trigger this response.

Implications of mast years

It's thought that in mast years, incidences of Lyme disease across the UK could increase. The increase in foraging materials for small mammals such as mice causes booms in their populations. Mice carry this tick-spread disease so the more that survive the winter, the more ticks they will infect in spring.

Our Nature’s Calendar project records a number of seasonal events including amount of fruit for species such as oak and beech. Have you seen an exceptional amount of fruit on these species this year? Get recording and help us to determine whether or not we are in a mast year!

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