The social networks of trees

Canoeing through Edmonton’s river valley this fall reminded me of the connections between some plants. Trembling aspen trees do produce seeds but their main means of reproduction is through runners. These runners result in colonies of genetically identical trees. The fall emphasizes this as entire patches of trees will all change colour at the same time.

I don’t really think about coniferous trees (ones that produce cones) having any of this type of connection between individuals. And it certainly is different from the system of runners produced by the aspens. But new research out of the University of Alberta shows that adult Douglas fir trees do indeed have a network that connects them. But their network is created by fungi.

New research by Birch et al (2020) reveals that the number of connections that adult Douglas fir trees have with other tree’s through underground networks of fungi called ectomycorrhizal networks influences the tree growth. Ectomycorrhizal networks are fungi that create a lattice around the roots of the trees. They do not enter the cells of the tree. The networks allow the trees to take advantage of nutrients absorbed by the fungus, but the trees can also use the network to share resources so that those that have (sources) can share with those that have not (sinks), something many humans could learn from.

Specifically, Birch et al found that the number of other trees connected to each other by one species of fungus was associated with the amount of annual growth of the individual trees. More connections were associated with higher growth rates.

This is an interesting finding in light of recent media about governments committing to planting trees in order to combat climate change. The thing about trees and climate change is that the tree needs to survive and thrive for many years in order to contribute to reducing greenhouse gases. Therefore, we need to not just plant the trees but also make sure they survive. And this research is just one piece that emphasizes the importance of what is happening around the tree for its survival. So, regardless of the photo ops that politicians may want, planning for planting trees needs to consider many more factors than just how many trees are put into the ground.