Leon Vlieger in The Inquisitive Biologist:
The idea that trees communicate and exchange nutrients with each other via underground networks of fungi has captured the popular imagination, helped along by the incredibly catchy metaphor of a “wood-wide web”. Suzanne Simard, a Professor of Forest Ecology at the University of British Columbia, has developed this idea more than anyone else and happily talks of mother trees nurturing their offspring. This idea has not been without controversy in scientific circles, if only for its anthropomorphic language. I was both sceptical and curious about her ideas. High time, therefore, to give her scientific memoir Finding the Mother Tree a close reading.
First, a quick biology lesson to get you up to speed. At the heart of this story are not just trees but foremost fungi. Except for their above-ground fruiting bodies that we call mushrooms, fungi largely weave their way unseen through soil, decaying wood, and other substances. Here, they form mycelium: networks of fine tubular cells.