What's Your Snag?

Until recently, my wife and I had a dilemma that was stalling the preliminary landscape work on our property. There were seven really large alder trees that I reluctantly had to admit were a safety liability. For one, they were directly next to our drain field. After we moved in, Envirotek (the septic company) and Housing Hope (the house-building program facilitating the whole project) gave conflicting information about what to do with these trees. In general, they stated that large trees should not be anywhere close to the drain field (Envirotek specifically states that trees should be at least 30 feet away), since the roots will seek out moisture and interfere with the tubing in the drain field. However, despite their strong recommendation, they kept the trees in place, and have not wanted to acknowledge that they should have been removed to ensure the proper functioning of the septic system. It’s only logical that the roots will continue growing toward the water and wrap around the tubing (even if the inside of the tubes are coated with material to prevent them from getting inside).

Even besides that, alder trees are short-lived and weak-wooded to begin with. My wife and I had observed these trees swaying and cracking in the wind, and lots of branches were dropping in the yard, often impaling the septic field. There weren’t any stronger trees immediately nearby to provide a windbreak. A few of the alders were leaning significantly, and it was only a matter of time before the trees themselves cracked or got uprooted. They were tall enough that, depending on which way they fell, they would either damage a house, damage our septic system, or fall across the street.

I say all this because despite these clear problems, I wanted to keep them, and I agonized a while about whether or not they needed to go. The birds loved perching in these tall trees, and I hated the thought of disturbing more of the local wildlife in addition to what already had to be removed for the house. Yes, I was being sentimental about alders, even though I'm fully aware they are a short-lived pioneer species. It wasn't an easy decision, but after observing them for a year, it was obvious they needed to be cut down.

In March we went forward with the removal, but we did something a little unexpected. We purposefully kept several feet of each tree trunk, which admittedly looks a little odd. These trunks of dead or dying trees are called "snags," and they have an important role in forest ecology. This is a good summary from Wikipedia:

Snags are an important structural component in forest communities, making up 10–20% of all trees present in old-growth tropical, temperate, and boreal forests. Snags and downed coarse woody debris represent a large portion of the woody biomass in a healthy forest. 

In temperate forests, snags provide critical habitat for more than 100 species of bird and mammal, and snags are often called 'wildlife trees' by foresters. Dead, decaying wood supports a rich community of decomposers like bacteria and fungi, insects, and other invertebrates. These organisms and their consumers, along with the structural complexity of cavities, hollows, and broken tops make snags important habitat for birds, bats, and small mammals, which in turn feed larger mammalian predators. 

Snags are optimal habitat for primary cavity nesters such as woodpeckers which create the majority of cavities used by secondary cavity users in forest ecosystems. Woodpeckers excavate cavities for more than 80 other species and the health of their populations relies on snags. Most snag-dependent birds and mammals are insectivorous and represent a major portion of the insectivorous forest fauna, and are important factors in controlling forest insect populations. 

Frequent visitors on our snags. It's a good place to keep an eye out for cats and other predators.

It's a simple yet important concept, and that's why we chose to keep them. Snags are encouraged by the Washington Department of Fish and Wildlife as one part of creating backyard wildlife sanctuaries (https://wdfw.wa.gov/species-habitats/living/backyard#improving-property). In addition to the snags, we also had the arborists chip most of the wood onsite, and we're keeping the larger pieces for future landscaping projects (logs for hügelkultur, bordering garden beds, etc.). It's not the prettiest sight to behold, but there is a long-term plan in the works. Eventually we'll plant trees and shrubs close to the snags (but still a good distance from the septic field), and these columns of decaying wood won't look quite as startling as plant life starts to fill in around them. Don't overlook the creative potential in these natural habitats.

Here are some other examples of snags that have caught my attention lately:

A snag right next to a camper cabin in North Bend, WA.

It was tragic when we discovered this magnificent old Doug fir starting to uproot next to a house in Lake Sammamish, WA. Thankfully they chose to keep this snag here, and birds and other critters are still able to perch on the remains.

A snag in an urban Seattle forest.