Oaks and acorns

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Dr Ryan McClory spent three years at Wytham investigating oak masting. 

This is an unusual feature of the reproductive cycle of certain tree species, including oaks in the UK. There are big variations in how many acorns each tree produces each year, and these are synchronised in trees all over the country. 

Every few years, there is a so-called 'mast year', in which oaks produce huge numbers of acorns together, carpeting the floors of woods all over the UK. 

Some theories suggest this protects oaks against seed predators like acorn weevils. The trees starve the predators during poor seasons and reduce their numbers. This means when the mast year comes they can't take full advantage of the glut, and many acorns survive to become young trees. 

There is still a lot we don't understand about this strange phenomenon, and Ryan's research at Wytham Woods has revealed new layers of complexity. By measuring how many acorns trees in different parts of the Woods produced over several years, he found that many of them don't actually make the same quantity in the same years as their neighbours. Some that are on heavy clay soils with plenty of sunlight are 'super-producers', with a good acorn crop every year. 

Ryan also looked at the impact of pollinating oaks in certain areas by hand. His results suggest that poor acorn years are often simply a matter of too little pollen in the air. 

Read more about Ryan's work - or watch our video on oak research at the Woods.