2020 will be remembered as a mast year (and possibly for other reasons). But why?

Mast years are when trees across the country produce a bumper crop of fruit or nuts. This was very striking in the woods at Charley two weeks ago when the acorns were raining down on my head. Mast years are thought to be advantageous for the trees as they swamp animals which eat the seeds so that a proportion will germinate to form a new generation of trees. 2013 was the last big mast year, but why do they occur?

The simple answer is - we don't know. As the phenomenon tends to occur across the whole country it is clearly not down to local factors. Weather is thought to be involved, with the right combination of temperature and rainfall in the spring being needed. The weather was certainly nice around the start of the first lockdown. The trees produce lots of flowers, but in addition, since Oak trees are wind pollinated, a dry and warm spring is needed. On the other hand, producing lots of fruit is costly and reduces the growth of the tree, so they don't want to do this every year. What will happen in 2021? Probably not another mast year, whatever the weather, because trees have spent a lot of energy on fruiting this year. And likely, a boom in rodents and Jays that will have a good winter feasting on acorns.