Ethan Tapper, Chittenden County Forster

Are trees individuals? I started to think about this question after hearing a researcher say that trees are “colonial organisms” — more like colonies of autonomous branches than individuals. As I struggled to find answers, I found that this topic is as nuanced and as complex as our forests.

While humans and other animals are unitary organisms — with a single body — plants and trees are modular organisms, comprised of repeating “modules.” Unlike unitary organisms, modular organisms like trees are unconstrained by the determinate growth of a human or animal body. Instead, they have an indeterminate growth pattern, able to repeat themselves over and over again by creating new roots, branches, buds and sometimes trunks.

Butternut tree.

Butternut tree.

While branches are connected to a common trunk and root system, they may also behave autonomously, competing with each other for light and satisfying their own energetic needs before exporting resources to the rest of the tree. When they are shaded (or otherwise consume more than they produce), they die.

Though they have some autonomy, a branch is also part of a tree, an organism that must maintain its overall shape and growth pattern to survive. Trees regulate their overall growth largely through processes known as apical dominance and apical control, using hormones to suppress the growth of certain buds and branches. Trees with high apical dominance and apical control — like conifers — are excurrent, resulting in a relatively symmetrical shape. Shrubs are decurrent, with low apical dominance and low apical control, creating an asymmetrical growth pattern of many competing stems. Deciduous trees fall in between these extremes, with a more-or-less symmetrical (excurrent) overall growth pattern within which each branch is somewhat decurrent.

With some species of trees, such as eastern white cedar, branch autonomy is especially pronounced. Cedars form stem strips: sections of bark that connect groups of branches directly to groups of roots. When exposed to drought or other stressors, a single stem strip and its associated roots and branches may die while the rest of the tree is relatively unaffected.

Some tree species produce clones — sprouting groups of genetically identical trees from their root system. Covering over 100 acres in Utah, an aspen clone called Pando is the most massive and perhaps the oldest organism (some would say clonal organism) on Earth, weighing an estimated 13 million pounds and thought to be between 14,000 and 80,000 years old. While Pando looks like a forest of young aspen trees, each tree is a ramet — genetically identical and connected, at least initially, to the same root system. To think of these ramets as individuals is both right and wrong: they compete with each other for light and even for resources within their common root system, but are also indisputably part of a larger entity.

Many of us have been captivated by the idea of the “Wood Wide Web,” the underground networks of mycorrhizal fungi that can connect trees together, even facilitating communication and resource-sharing between trees. While some have taken this research to mean that forests are unified entities, or that they are entirely cooperative and altruistic, the truth is more complicated: while they cooperate at times, trees also compete with each other — often to the death.

Like a branch on a tree, a tree in a forest is both autonomous and dependent on a larger system. Even a small forest is comprised of billions or trillions of organisms, each living an autonomous, complex life. Trees rely on other organisms to build soils, to regulate populations of pests, for pollination and seed dispersal — and much more. Together, these countless independent organisms, their environment and natural processes form a natural community: an entity with behavior and properties of its own. As the fate of a branch is linked to the fate of the tree to which it is attached, the fate of a tree is inextricably linked to the fate of this natural community.

Like us, a branch on a tree or a tree in a forest is an individual, but also part of something greater. As we exercise our autonomy as forest stewards, it’s up to us to recognize our part in the bigger picture, to learn how to sustain ourselves while also sustaining the trees, the forests and the living landscape to which we are connected.

Ethan Tapper is the Chittenden County Forester for the Vermont Department of Forests, Parks and Recreation. To see what he’s been up to, check out his YouTube channel, sign up for his eNews and read articles he’s written.