Leaves fall in autumn. At least, they tend to do that if they hang on deciduous trees in temperate climates. Here, the months of October and November are dedicated to splendid colour displays and hours of raking leaves into piles.

It is a simple fact, this falling of leaves, and we all have seen it ample times. But even though the fact itself might be simple, there is a lot we do not understand about the why and how, and especially when.

Do the leaves fall becauses days get shorter? Do trees base their decision to shift colours entirely on this reduction in the so-called ‘photoperiod’? But what if they do? The decrease in daylength is a predictable factor in autumn over the years, but what if the temperatures start to change under the influence of climate warming? What if a tree is running out of nutrients? Do they take all these other factors into account, and which one of these will be decisive?

It is only when my colleague Matteo Campeoli recently got funded a big European project to find the answers on these questions, that I realised what a big mystery autumn actually is. And that struck me as a big surprise: how can we experience autumn year after year, and still not know such fundamental things?

Please, dr. Campeoli, make haste in finding the answers!