To grow or to reproduce?

The impossible choice.

In fact, as we shall see, it’s a triple trip-up.

Fagus sylvatica, these trees can be found from Sicily, way down south to southern Norway, up north. That’s about their northward limit as they need a growing season of at least 140 days. They are monoecious, both male and female flowers can be found on the same branch. In normal times they start reproducing at 40 to 50 years old, this is fine as they can live up to 300 years.

The Beech tree roots aid air-circulation in soils and the leaves are high in Potash which means they play an important role in maintaining soil fertility. They also like to hook up, in an Ectomycorrhizal kind of way, with several species of fungi.

That’s enough of an introduction to this wonderful tree, on now to its existential problems. Someone has been changing the climate and this has had unforeseen consequences for the Beech trees and, frankly, everyone else.

The Beech trees have had to decide between two things, grow or reproduce. In Europe, they have decided to do the latter. Beech tree growth rate seems to have declined, since 2005, by 28%, which is a lot. Both activities make energetic demands on the tree, any organism adapts to minimise energy needs and maximise the benefits accrued from any energy spent. All organisms are functional parts of ecosystems which means they are involved in many interactions with other species. They are also locked into the Earth’s climatic system and influence it in a multitude of ways.

Historically Beech trees, as I mentioned above, get a lot of growing in before they start to reproduce. The Beech mast as the fruit is called attracts a number of animals that enjoy eating it. The Beech trees have put some thought into how to deal with this problem and came up with the feast/famine strategy. The trees would produce a big crop one year and then a small one, this causes a crash in the populations of the Beech mast predators. The next big drop of mast falls onto a smaller population of predators.

Today Beech trees, as mentioned, have decided to put their energy into reproduction rather than growth. This means their fruit production is more regular, it’s been called ‘masting breakdown’. The old and tested strategy has broken down and the Beech mast predators are the ones who are winning out. This is bad, the trees are putting their energy into reproducing and their efforts are wasted as the nuts are simply eaten and so they are non-viable.

You may be wondering if droughts may be causing all of this but no, it’s not the case. The culprit is warmer temperatures in general.

If the Beech trees grow less then the amount of CO2 they lockdown is reduced. As their Beech mast is now so vulnerable to predators that few survive to grow into new trees their place in European forests is endangered. If you want to check out the original research you can find it here.

This is one example of something people designing agroforestry systems have to deal with. Confronted with a rapidly changing climate and its impacts on rainfall, soil life, and more, it is sometimes difficult to know which types of trees to plant. They are long-lived, a walnut tree (Juglans regia) can live for 200 years. On planted today could live until 2225, a date we rarely see even in long-term climate forecasts. We can only imagine what the climate in Southern Europe will be like then.

To the rewilders amongst us this study brings up similar questions, basically the 3 Ws, what (type of tree), where (to plant them) and when (they should be planted).