A common misconception one might have while observing a standing dead tree, also known as a snag, is that the health of the forest is declining. While an abundance of dead, diseased trees can be cause for concern, a forest comprising of 5-10% snags is an indication of a thriving ecosystem. Trees die and become snags for a variety of reasons, including but not limited to drought, wildfire, disease, and parasites. Although some people may see these skeletal, leafless structures as visually unappealing or safety hazards, they are fundamental in fostering biodiversity in forest communities. Snags offer sustenance and refuge for a myriad of wildlife species, serving as a site to create nests, seek shelter, perch, and forage for food.
One of the primary roles of snags is providing shelter, particularly for cavity-nesters. “Cavity-nester” is a term used to describe birds and other animals that form nests and lay eggs in an excavated chamber — in this case, a hollowed-out snag. There are two types of cavity-nesters: primary and secondary. Woodpeckers, for example, are primary cavity-nesters because they create their own cavities. Woodpeckers typically produce multiple nesting cavities in a year — each taking three to four weeks to complete — but rarely revisit them in consecutive years. Luckily, their hard work does not go to waste! Once a cavity is vacated, it becomes a new home for secondary cavity-nesters such as owls, ducks, swallows, bats, squirrels, and other tree-dwelling species that are unable to create their own shelters.
Snags also make for excellent, multifunctional perching locations. Perching spots can be used as a place for birds to rest, hunt, and sing a blissful tune. Often, tanagers and flycatchers will use these dead branches as song perches. Smaller branches may be used as a song perch by hummingbirds, bluebirds, and other small songbirds as a way to attract mates and declare their nesting territory. Due to their lack of foliage, snags have a limited ability to absorb sound, which creates a highly conducive environment for echoes to reverberate. Another benefit of snags having no foliage is that birds can have a clear scope of their area. If close to a field, perches will be used by owls and hawks as a hunting spot. These raptors will perch on a snag and wait for voles, mice, and other possible prey to unassumingly pass by below. Kingfishers, eagles, herons, and osprey are some of the key hunters that utilize snags as perching spots near the water.
Foraging is an additional ecosystem service that snags provide wildlife. As a snag deteriorates, it softens and attracts insects that thrive and reside within the wood. This abundance of insects serves as a source of nourishment for a wide range of wildlife species. In fact, nearly 45 distinct types of birds, mammals, reptiles, and amphibians use snags as a means of locating food that is stored within them. Mammals such as squirrels, porcupines, raccoons, and martens are among those that utilize hollow snags and large knot holes as ideal places to forage for sustenance.
As a snag progresses through the decaying process and falls to the forest floor, it transforms into a log, triggering the emergence of a new ecosystem, one that accelerates the log’s decomposition. The decomposition process begins when fungi, such as mushrooms, colonize on logs. Fungi play a pivotal role in breaking down dead organic matter such as logs, breaking the material into smaller components, and facilitating the release of essential nutrients into the soil. The process is further facilitated by bacteria, slugs, ants, lichen, and many other decomposers and detritivores. In the advanced stages of decomposition, earthworms actively consume and break down the remaining wood, incorporating it into the surrounding soil as nutrient-rich castings. This process not only contributes to the recycling of nutrients but also enhances soil fertility, allowing for the growth and sustenance of a diverse array of plant life.
Snags are an essential part of the forest habitat, and they play a crucial role in maintaining the ecosystem's health and sustainability. So while they may not look pretty, they're doing important work behind the scenes. Removing snags can have devastating consequences, including habitat loss, a reduction in biodiversity, and disruption of important ecological processes like nutrient cycling. It's advisable to avoid disturbing snags, whether in your backyard or in a forest. Snags are highly beneficial to the ecosystem, and you can even opt to intentionally add logs to your property. This will attract native birds and other wildlife species, giving you an opportunity to witness firsthand the numerous ways in which snags can enhance your local environment.