A Tree’s Part in the Forest Circle of Life

As we confront tree deaths from disease, climate change, and weather, how should we think about either removing or leaving them be? What are the costs and benefits?

Standing dead trees are called “snags”, and those on the ground are called “coarse woody debris”, or simply “logs”. They are important habitats for a variety of wildlife and plants, and form a vital part of the forest ecosystem. A snag with a diameter of at least three inches and standing a minimum of six feet tall offers value to wildlife. The larger the snag, the higher its wildlife value. Snags are either hard or soft, depending on the stage of decay, and different animals may prefer either type.

Snags provide shelter for many birds, mammals, reptiles, and amphibians. Nesting birds use them, including owls, woodpeckers, kestrels, and ducks. Insectivorous cavity-nesting birds form the vanguard in controlling forest insect populations. In addition to shelter, snags also provide a place to perch for many species of birds, from small flycatchers to great eagles, hawks, and owls. More than thirty different mammals live in snags as well. They include bats, opossums, squirrels, mice, porcupines, racoons, and bears.

Coarse woody debris, often both a fallen tree trunk and its limbs, nurtures a wide range of plant and animal life. Decaying tree parts recycle nutrients by supporting insects and fungi whose activity puts microbes and organic material into the soil. Rotting logs, known as “nurse logs”, often create microhabitats for young tree seedlings. The damp environment under logs serves as a refuge for insects, salamanders, and snakes. Hollow logs provide shelter to foxes, coyotes, turtles, snakes, shrews, and sometimes even bears. Finally, snags and logs, by virtue of promoting insects and mushrooms, offer a rich source of food to forest creatures.

In evaluating a dead or dying tree on your property, you should assess the risk to structures, people, and roads. Trees that pose a high risk, of course, should come down. However, you can figure out whether you need to take the whole tree down, or whether you can leave six feet or more of the trunk standing to create a snag. Might you leave some or all of the tree parts, or slash, where they fall? Can you shift them deeper into your woods rather than having them chipped or hauled away? Strewing slash in a naturalistic way rather than piling it allows it to do its job.

Today, we face the precipitous deaths of our ashes due to Emerald Ash Borer (EAB). They offer a case study in how to think about dead trees on your property. Preemptively removing those at high risk to structures and roads can save you money. Cutting them before death is cheaper than waiting until they are dead because dead ash, in particular, is unpredictable and more dangerous to the workmen.

What about the rest of the ash trees? There is no reason to cut them down and many excellent reasons to leave them standing. First, removing them will not affect the progression of EAB. Second, they will provide valuable ecosystem services in their new role as snags and coarse woody debris. Third, there is a chance you have a partially resistant ash that could survive to be used later to breed more resistant native ash for replanting.

If you’re interested, here is a link to the lingering ash program called Monitoring and Managing Ash.