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Chestnut plantation, mushroom cultivation and some evolutionary biology

This winter I’m going to plant 6 grafted Corsican chestnuts provided by the Groupement Régional des Producteurs et Transformateurs de Châtaignes et Marrons de Corse. This autumn, Tom (a Wageningen University student who has been helping me for a few months) and I cleaned the land (getting rid of the brambles mostly) where I want to plant the chestnuts. It’s a hilly piece of land with good soil directly below my fenced land ‘invaded by’ different trees (such as holm oak, dead chestnut, hazelnut, ash and lime tree). Before the abandonment of this land, it used to be a chestnut orchard based on the huge dead chestnut trees that can be found here.

The idea is to plant new chestnuts to replace the dead ones. However, I’m not going to clearcut the land just to plant 6 tiny chestnut trees. Instead, I’ll thin this forest by carefully selecting holm oak trees. Why? Because you can grow mushrooms such as shiitake and oyster on holm oak logs (more on that below). Furthermore, it’s great to plant young chestnuts in a forest-like environment rather than in a clearcut area because of the microclimate ; the presence of some big trees protects the young seedlings from wind and sunscald stress and greatly improves the local microclimate.

Moreover, recently it’s been discovered that different tree species can transfer nutrients, water and even carbon (energy) between each other via the mycorrhizal network (which is the extensive network of fungi that live in the soil). Researchers found that birch and douglas fir shuttle carbon back and forth to one another seasonally via their ectomycorrhizae. In winter, when birch don’t have leaves, they receive carbon from the douglas fir trees and in summer, especially when the douglas fir is shaded, it gets carbon from the birch trees (or more specifically from the mycorrhizal fungi linking the two species).

In another study, two different species were planted together in one pot. When researchers pulled all the needles of the douglas fir seedling, it sent stress signals that stimulated strong synthesis of defensive enzymes to its neighbour. Moreover, it sent a lot of stored energy (‘food’) to its neighbour (more info here The question is why?

By doing this, the douglas fir seedling drastically reduced its own survival and reproductive chances. According to evolutionary biology, this kind of ‘behaviour’ should thus be limited because it leads to reduced fitness. So, why does the douglas fir seedling seem to act altruistically ? We don’t know for sure. Different theories exist. It might be a passive flow of nutrients/carbon from a high concentration to a low concentration via the mycorrhizal fungi.

Another explanation would be that by exporting carbon to its root network, the douglas fir benefits nearby trees that have a high likelihood of being close relatives such as offspring. The fact that it reaches another species and not only douglas first could indicate that the trees are not in control but rather the fungal network in determining where the carbon goes.

Another theory hypothesizes that the fungus acts in its own interest; as it is connected to many different trees, it might try to optimize its own carbon input (via healthy trees). Diseased trees have deleterious effects on the long-term resilience of the fungus’ carbon inputs and the fungus might therefore ‘decide’ to support healthy trees rather than diseased ones as an investment in its long-term survival.

Many theories, but no one knows yet who’s in charge, how this works and more details.

What I like to conclude from these studies is:

-don’t disturb the soil (ploughing) because it breaks up mycorrhizal networks.

-always keep as many living plants as possible to have a continuous influx of carbon to the mycorrhizal network

I use this base as much as possible for my food forest and even my no-dig market garden. Coming back to the plantation of the grafted Corsican chestnuts, I believe that the old trees present on the land where I’ll plant the chestnuts will help establish the chestnut seedlings via the mycorrhizal network. Yes, it’s true that those older trees will create some shade that reduces the potential growth rate of the chestnuts (less light, less photosynthesis), but taking in consideration all the benefits provided by the presence of these trees, I’ll keep them until the chestnuts are at least 5 years old and they are well-established. Then, at some point I will start pruning the big trees to provide more light (because chestnut trees need full light when mature for high fruit production) to the chestnuts.

Concerning the mushroom project, I’ve successfully inoculated around 40 holm oak logs with both shiitake and oyster mushrooms. The process is rather simple:

-drill holes (about 40-60 holes per 1 m of log)

-hammer in the mushroom plugs (wood inoculated with the mushroom - you can buy this online)

-seal the holes using (bee) wax

-keep the logs in a shady location and wait at least a year to allow the mycelium to colonize the logs

I expect the first minor harvest of oyster mushrooms in autumn 2022 or even in spring 2023. It takes a while but the logs will continue to produce for about 5 years.

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