To understand how to take care of forests, we first need to understand what they are and how they work. While most peoples’ understanding of them starts and ends with trees, forests are complex, dynamic communities comprised of many different organisms and the processes that affect them. While forests function as systems in many ways, they are not utopias. Organisms compete with one other, parasitize each other, eat and destroy each other. Within forests, one of the incredible processes that make forests work – and one that we need to learn to accept – is tree death.
When trees die it may seem startling or sad; the end of a decades or centuries-long life, the loss of a once-beautiful and healthy living thing. To the forest, however, the death of a tree is something much more profound; supporting critical ecological functions and processes and providing habitat for many native organisms. I think of a tree as having a “biological life,” (when it is “alive” in a traditional sense) and also an “ecological life” (the tree’s overall influence on forest ecology, which can persist for decades or centuries after it dies).
The death of a tree can happen in a moment – like when they are snapped or uprooted in a windstorm—but it usually happens over time, the product of numerous interrelated factors called “stacking stressors.” For instance, a tree’s branch is broken by heavy ice and snow. This wound is colonized by fungi, which breaks down and softens the tree’s wood, paving the way for wood-boring beetles and other arthropods (bugs). Searching for these bugs and their larvae, woodpeckers excavate “cavities” (holes) in the tree. Cavities create still more opportunities for fungi, bacteria and arthropods to colonize the tree. As these stressors compound on one another, the stress eventually becomes too much and the tree dies.
Tree death is often a biological process; the product of a rich assemblage of organisms taking advantage of their natural habitat. While it’s tempting to vilify fungi, bacteria and bugs for “killing our trees,” a more holistic understanding of forests reveals that these organisms are actually critical parts of ecosystems. They help break-down and recycle dead trees and plants, enriching soils and feeding future generations of trees. In facilitating tree death, they create “snags,” (“dead-standing” trees) and “cavity trees,” both of which are used by a huge number of animals as nesting and denning habitat. Once the tree falls, “dead” wood on the forest floor stores carbon, improves the forest’s ability to absorb water, provides a place for trees like yellow birch and hemlock to take root, and provides habitat for underground mycorrhizal fungal networks critical our forests’ ability to function. Dead wood is critical habitat for salamanders, the “apex predator of the forest floor,” which account for the most biomass of any vertebrate predator in the northern forest (meaning that if you weighed all the coyotes and all the salamanders in the forest, the salamanders would weigh more). Dead trees are such a rich habitat that they can contain as much as four times as much living biomass as living trees.
Tree death also provides opportunities for forests to become diverse and complex. Openings in the forest canopy are soon filled by “regeneration,” the abundant growth of young trees and plants. Over time, this cycle of death and regeneration creates forests with a rich mosaic of different sizes, ages and species of trees. Forests like this supporting a diversity of bird and wildlife species, store more carbon and are more resilient and adaptive in a changing climate.
As a forester, my main concern is keeping the forest, as a system, healthy. To this end, tree death, just like tree life, is something to be celebrated, not avoided. It can even be something that we use as a tool in our stewardship of forests; using the cutting of trees to create a more diverse, complex, and resilient forest, one that is full of life in a more holistic sense.
While it might make us uncomfortable, understanding the profound and important role that tree death plays in forests is a critical part of learning how to take care of them. We should strive not to keep every tree alive, but rather to keep the forest vibrant and whole. Healthy forests not only tolerate death – they require it.
Ethan Tapper is the Chittenden County Forester. He can be reached at ethan.tapper@vermont .gov, (802)-585-9099, or at his office at 111 West Street, Essex Junction.