My studies in ecology have been influential in my work as an arborist. Ecology is the study of the interconnectedness of all things on this planet – humans included. We don’t live in a bubble and all of us have little (or big) ecosystems right outside our door, which formed around and in reaction to our human activity. As arborists, we are responsible for taking care of some of the greatest ecosystem engineers of all – trees.
In ecology, we use the term “keystone species” to describe a species (often a predator) whose effect on its ecosystem is so large that, without it, the ecosystem could collapse. These organisms play a pivotal role in how their ecosystem functions and no other species can fill their role.

I was thinking about this while watching the single large tree I have in my yard. Birds fly in and out its canopy constantly, squirrels run down the trunk, edible mushrooms even grow in the spot where decay is present. Underneath this tree grows flowers and berries of all kinds, which I share with the birds and bees. Since adding a large wood chip bed, there’s lots of mycorrhizal activity – fancy way of saying good fungi! The fungi and roots of this tree absorb rainwater and prevent runoff, as well as stabilizing the whole hillside it lives on. When this tree leafs out in the spring, its sheer biomass (leaves making oxygen and wood sequestering carbon) never ceases to amaze me. It shades part of my house and my entire backyard, making it a cool oasis in the summer

My tree, a box elder named “Grandpa”

While it might not be tied to a specific species, surely this is a keystone organism in my yard. Without this tree my yard would be dramatically different, and many of the other species that make use of this micro-ecosystem would be unable to do so without this tree. For reference, I’ve counted at least 60 species of plants, fungi, birds, insects, and small mammals that either live around or frequent this tree. For a suburban yard, that’s pretty incredible! 

I encourage everyone to take a walk around your yard, and think about your trees and shrubs and all the species they might support. Do you have a keystone tree or shrub? Size doesn’t matter! In ecology, a keystone organism can be as small as ocean coral or the mighty beaver. Perhaps it’s just a tree you love, one you can see out your window or one whose fall color you look forward to. Think about what your home, your personal ecosystem, would be like if you lost one of your trees.

We must be good stewards to all of our trees, but especially those we see as keystone organisms. Maybe pick out one tree in your yard that deserves extra attention. Monitor it for pest problems. Mulch it generously. Have an arborist assess it for potential issues or even regenerative pruning. Learn about it, learn its name and learn what it likes. Spend time watching it and see how many species you can count hanging around. You don’t have to know their names, plants with three leaves and red birds are good enough. Take care of your keystone tree, because it’s taking care of you.