Social Butterflies, Social Trees

By John Heddle

Trees: beautiful, important, but social? We know they are often long-lived but are they neighbourly, considerate of the young, and helpful to others? I never thought so. I thought that they were fierce competitors, especially for light but probably for nutrients in the soil and water, too. New research shows, however, that I was wrong. They are social organisms. Moreover, their cousins including small flowering plants, are family oriented as well.

The sociality of trees is a relatively new finding in which Suzanne Simard at UBC played a critical role. Professor Simard discovered that the extensive network of roots in the forest is a pathway for communications among trees and that this is facilitated by fungi growing on the roots. My now-dated, view of fungi was that they were simply breaking down leaves and twigs for their own use. Careful studies show, in contrast, that the fungi and the trees live in mutual co-operation, each helping the other. The fungi gather nutrients from the soil and pass them to the tree roots. These can be nitrogen, which the trees cannot “fix” from the air themselves, minerals like magnesium and calcium, and water. The tree roots reciprocate, giving the fungi sugar which they can use for energy and for construction. The fungi can also pass sugars into the roots of a different tree, thus providing a channel of communication between the trees. Large trees can supply sugar to a shaded sapling which would otherwise die – effectively of starvation. Moreover, the trees favour others of their own species over members of other species. This is not exclusive as members of other species also get help in the form of sugars, just to a lesser extent than kin get. Simard views the forest as a neighbourhood in which the neighbours cooperate. You can see her in a You-Tube video called Intelligent Trees. It has more than 100,000 views.

These results are important for the forestry industry as logging practices might be altered to permit a “mother tree” to remain to feed new seedlings as the forest regrows.

More recent studies of small flowering plants also show interactions between plants, and not merely competitive struggles for space and light. Plants of different species were found to invade each other’s territory, a Darwinian struggle. But when the neighbouring plants were of the same species, each plant restricted itself to a smaller space. The congregated family of such kin also tended to flower together.

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