Forest health is a topic on the minds of many people these days. Healthy forests are the key to resilience and adaptation, addressing the biodiversity crisis, and supporting a viable forest economy. All too frequently we are reminded of new and ongoing threats to the health of Vermont’s forests; non-native invasive plants and pests, overpopulation of white-tailed deer, and climate change to name a few. As we consider how to steward our forests to improve their overall health, it stands to reason that we want to promote the health and vigor of individual trees as well. While this is true, it is essential we also recognize that dead wood, both standing and on the ground, is just as much a part of a healthy forest ecosystem as live trees are.

Dead wood comes under many monikers. Standing dead trees are often referred to as snags. When those trees ultimately fall to the ground the twigs and small branches, generally less than 4 inches in diameter, become fine woody material. The trunks and larger branches can be described as coarse woody material. Within these different classifications, not all dead wood is created equal. How sound or decayed the wood is provides an additional way to look at it. It can be helpful to consider stages of decay when developing our understanding of the ecological role that a particular dead wood feature plays within the forest.

Speaking of ecological roles of dead wood, what are they? Why is an abundance of standing dead trees and dead wood on the ground a critical component of a healthy forest? Perhaps the most commonly understand value is that standing dead trees, snags, provide habitat for everything from birds and bats to flying squirrels and fungi. By some estimates, roughly ¼ of northeastern wildlife species utilize snags for all or a portion of their life cycle. Pileated Woodpeckers will seek out larger (~20 inch diameter) and minimally decayed snags for perching, foraging for insects, and excavating a nest cavity. Little brown bats may be found roosting in more decayed, hollow snags. Regardless of the wildlife species, the larger the snag, generally the greater the habitat value. Eventually all trees, alive or dead, will fall to the ground, adding to the amount of coarse and fine woody material on the forest floor. While this may appear “messy” at first glance, once the ecological values of down woody material are understood, it can become quite beautiful. Those larger logs may provide a courtship “drumming” site for male Ruffed Grouse. They may also be chosen by black bear as a place to which underneath spend their winter torpor; a period of light sleep, decreased breathing and heart rate, and lower metabolic rate. The tops of those fallen trees provide great cover for a variety of small mammals and songbirds. They also provide tree seedlings and small saplings with protection from being easily browsed by deer. Both coarse and fine woody material can help slow, spread, and retain water; a key consideration in thinking about how to support our forests in being more resilient to extreme weather events in a changing climate.

Two additional topics related to dead wood that are currently receiving a great deal of attention are old-growth forests and forest carbon. Old-growth forests have abundant large-diameter snags and downed dead wood in various stages of decay. In fact, it is estimated that old-growth forests often have two to four times the amount of dead wood on the forest floor than is typically found in second-growth forests. Dead wood of all types also plays a crucial role in carbon sequestration and storage within forest ecosystems. Sound pieces of dead wood can keep carbon locked up for many years. As the wood decomposes, some carbon is released to the atmosphere. A significant amount of the released carbon however gets captured by fungi and other decomposers and stored in the soil. If one’s interests lie in managing forests for old-growth characteristics and/or carbon sequestration and storage, giving due consideration to current and future dead wood is paramount. But how much is enough?

Guidance on how many snags or pieces of coarse woody material to retain or recruit per acre is wide-ranging and somewhat dependent upon overall forest management goals. A forest where the primary goal is to develop old-forest characteristics will undoubtedly strive for more snags than a forest where maple syrup production is the highest priority. There are some general recommendations however that can serve as a starting point. Audubon Vermont suggests a target of at least 6 snags per acre, with one tree greater than 18 inches in diameter and three greater than 12 inches. When it comes to fine woody material, Audubon recommends leaving as many of the tops of harvested trees, often referred to as slash, in the forest as possible. No need to lop those tops to a pre-determined height (often 4 ft or less), simply leave them as they fall. In “Restoring Old-Growth Characteristics to New England’s and New York’s Forests” (2022), Tony D’Amato (UVM) and Paul Catanzaro (UMass Amherst) offer benchmark’s for snags and coarse woody material. Where restoration of old-growth structural characteristics in a northern hardwood forest is a primary objective, they suggest a target of 16-20 trees greater than 20 inches diameter be recruited and/or retained onto the forest floor as coarse woody material. For standing dead trees that recommendation is 8-12 trees greater than 20 inches diameter.

Regardless of ownership goals, intentionally planning to maintain current and recruit future dead wood in the forest will go a long way toward promoting overall forest health, resilience, biodiversity, and wildlife habitat.