Ah, trees. Those leafy icons of life and nature, inspiring writers through the ages…
In the forest, trees exist in many life phases simultaneously, from seedlings to giants, and then as standing dead trees (snags) and down logs. Natural forces constantly work on trees, causing them to grow, then die, crack, and rot. The individual fate of a tree can vary tremendously depending on many factors including; species, wounds, rot, soil moisture, wind, branch breakage, lightning and more. Dead trees are an essential part of forest ecology.
Wildlife Species that Benefit from Woody Habitat Structures
Well over 100 species of wildlife in Pacific Northwest forests depend on dead wood for crucial habitat. Animals such as woodpeckers, songbirds, squirrels, salamanders and owls use these woody structures as places to feed, and as cover for resting and reproduction. The solid woody cylinder of a dead tree can be a boon for these animals, particularly if in a configuration that encourages wood rot while providing woody structure.
“Wildlife tree” refers to those trees, living, dead or some of both, with dead wood features (holes, cracks, loose bark, etc.) providing habitats for cavity dwelling species. In fact, nearly one-third of our forest wildlife species must have some form of “wildlife trees” on their home range for survival.
The best type of natural wildlife tree may be a broken off snag, with adequate height and diameter to provide for multiple wildlife habitat needs. These trees will stand the longest, as the weight of the tree top is gone, softening rot proceeds down the stem from the top, and these woody structures can persist for many years. Look for these venerable habitats in the deep forest.
Human Activities can Mimic Habitat Creation Processes
People actively cut trees across the landscape for many reasons, including harvest, landscaping and site preparation. But rather than always removing whole trees, arborists and loggers can easily create long-lived, high quality wildlife trees by simply shortening (or “topping”) the tree to an acceptable height, and then leaving the cut stem for weather and woodpeckers to do their work creating valuable habitat.
Tim Brown is a pioneer in wildlife tree creation. He started making wildlife trees in the 1970s when working first as a logger, arborist, and then as a forest firefighter. He has a lifelong love for wildlife, and noticed many animals fleeing from fallen snags while he was falling timber. “I started thinking about it and would come home and make wildlife trees. I started in gardens and with landscape trees.” he said.
His business, Frontier Tree Service, near Lake Sammamish, was well-known for creating many wildlife trees, which still stand in National Parks (including Sequoia), as well as National Refuges, National Forests and greenbelts throughout the Northwest and across the country. He worked as a consultant to assist scientists and land managers with wildlife habitat projects around the world as well. Today, Tim works to share his expertise whenever possible with interested landowners, arborists and wildlife biologists. We went out to a private land near Snoqualmie to demonstrate some of his techniques for this article.
Selecting the ‘Right’ Tree
Trees to be made into wildlife trees should be solid enough to be worked, preferably by a qualified tree climber or someone working from a bucket truck. They also should be a long-lived species and in a location where future safety issues, such as dwellings, roads, etc., won’t demand that the tree come down. Tim recommends conifers, particularly Douglas fir, cedar or ponderosa pine, as preferred wildlife trees, as they tend to last longer. He points out, however, that all species can function, and broadleaf trees can be worked too.
We identified a clump of root-rot killed Douglas fir for our demonstration, well away from the road. Tim determined that a recently dead tree approximately 24” in diameter was sound enough to climb. After ascended the tree with climbing gear, he cut off the top about 45 feet up, and used a chainsaw to create a jagged top. A smaller, softer unclimbable, dead tree stood close by and he cut the top out of that one while leaning over from the first tree. Both were shortened enough that they have a higher likelihood of snag longevity after treatment.
Identifying “strike distance” to high traffic “targets” is a part of this selection. The overall height of the created wildlife tree should usually be less than the distance to the target, unless there is very little traffic. Remember that the shortened tree will have little “sail” or weight on the top, so is unlikely to simply topple over. In general, wildlife tree stubs fall apart in place over many years rather than falling over.
Removing the Crown
“Topping” trees is considered bad form for arborists working on valuable ornamental trees. However, this same technique can create high quality wildlife trees that will stand for many decades and provide habitat for many, many species.
(Side note: In logging units, a “hot saw” or mechanical tree harvester, can easily make short snags by cutting off stems at between 8 and 20 feet.)
Lofty Decisions
How much to cut off?
How much of the trunk to remove when creating a wildlife tree?
“We want the tree to stay up as long as possible,” says Tim, who recommends assessing potential wildlife trees for lean, overall stability and sway. In wind sheltered areas, more of the tree can be left. In general, the larger the diameter, the better. Tim suggests that the top diameter of cut trees should be at least 6” in order to provide enough wood for smaller cavity excavator species. Trees are generally cut 1/3 to 2/3 of the way up, resulting in a wildlife tree between 25 and 60 feet tall, though it can be higher if conditions allow it. Most branches are removed, with some stubs or short branches retained when possible.
“Sometimes I’ll leave some green branches so the tree dies slowly and remains stable longer,” notes Tim, adding that causing the tree to die slowly allows its still-living roots to hold it up longer.
The top of the wildlife tree should be “roughed up” with a chainsaw. This is accomplished by administering a series of v-shaped cuts across the top, then crisscrossing those with the saw from multiple horizontal angles.
“The top is jagged to better collect moisture and organic matter. Make it slightly concave in the middle to collect water,” Tim recommends. He also makes a few deep vertical cuts down into the stem at the top to help introduce water and rot into the stem more quickly.
Finally, banging on the cut top with the back of an ax will break off the flat surfaces and leave it looking entirely natural. This jagged top will provide more surface area to introduce rot into the stem.
Putting Cut Material to Good Use
The fallen top of the tree can be harvested as a saw log, used as firewood, or left on the ground to provide down-log habitat. Down wood has important value as habitat too, notes Tim, and offers other habitat features to work on, which we will describe in a future article.
Most managed landscape settings have a limited number of number of wildlife trees (those with soft dead wood that provide an opportunity for wildlife to create and use cavities). It has, and continues to be, a standard practice by many landowners to remove dead trees because of safety concerns or to use as firewood and other materials.
While the habitat value of wildlife trees becoming more widely understood, there remains a pressing need to create more of them by incorporating the maintenance and creation of these structures into routine management practices.
The time to create wildlife trees is whenever the opportunity exists, but particularly when there is a shortage of these structures in the forest. Ideally, there will be 6-10 of these tree per acre, with half of them in decayed soft condition and the rest hard.
Providing and creating wildlife trees is a simple and effective tactic for small forest landowners to encourage wildlife on their property. There’s lots of life in dead trees!
by Ken Bevis, DNR Stewardship Wildlife Biologist, ken.bevis@dnr.wa.gov, with Tim Brown, timothykbrown@msn.com
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