Fall is Tree Thinning Time for Forest Landowners

Ponderosa pine stand thinned and pruned
Ponderosa pine stand thinned and pruned to prevent spread of low-intensity ground-level fires into the crowns. Photo: US Forest Service.

Fall is just around the corner and for those who own forested land, if you have not already done so, you may want to consider thinning some trees out. People who own forested property are often hesitant to remove trees for various reasons. Why should you thin? What are the advantages?

Forest health

Many people think of a forest as a stand of trees existing together in harmony. In reality, a forest, particularly a young forest, contains trees competing with one another for their life-sustaining resources: sunlight, water, and nutrients.

There’s even a priority list of sorts within individual trees. It varies depending on the species but, in general, the order in which resources are allocated is, from highest priority to lowest priority:

  1. Maintenance of respiration
  2. Production of fine roots
  3. Reproduction
  4. Height growth
  5. Diameter growth
  6. Insect and disease resistance mechanisms, and
  7. Storage

A dense stand of tall, thin lodgepole pine, is a good example of a stand where there are enough available resources to allocate up to priority number 4, height growth, but not enough resources to allocate much to priority number 5, diameter growth, or beyond. This lack of resources will affect overall forest health, as the trees will not be able to allocate resources to insect and disease resistance mechanisms.

What sort of insect and disease resistance mechanisms do trees have? Let’s use bark beetles as an example, since certain species of bark beetles can cause extensive tree mortality.

In most coniferous species a resin duct system produces oleoresin when the tree is wounded, such as a broken branch. Oleoresin is basically a mixture of essential oil (turpentine) and nonvolatile solids (rosin). Oleoresin is considered the primary defense of conifers against bark beetle attack. Beetles that attempt to attack a conifer that is in good health and capable of producing adequate, pressurized oleoresin are typically immobilized in the resin or killed by drowning in it. The chemical makeup of the oleoresin is important as well, as some of the volatiles released from the oleoresin are toxic to bark beetles.

Dense stands, which tend to grow slowly, are consistently associated with bark beetle infestations. The susceptibility of a stand to bark beetle infestations may be changed by reducing competition between trees; in other words, thinning. In western North America, thinning has long been advocated as a preventative measure to reduce or alleviate the amount of bark beetle caused tree mortality. Thinning improves tree vigor and growth. It also decreases the likelihood of bark beetle attacks on individual trees by allowing the site’s available resources to be concentrated on fewer stems, which means trees will have enough resources to allocate to priority number 6 (insect and disease resistance mechanisms).

Wildfire risk reduction

Successful fire exclusion over the past 60 to 70 years has resulted in greater stand densities and a change in species composition. In that span of time, many forests in dry ecosystems, such as eastern Washington, have transitioned from fire-adapted, open ponderosa pine stands to dense pine and Douglas-fir stands. In moist forests, the change has been from open stands of western white pine and western larch to relatively short, closed stands of grand fir, western hemlock and western redcedar. These changes have led to an increase in the occurrence of crown fires (fire that spreads from treetop to treetop), the most intense type of wildfire, and often the most difficult to contain.

Thin from below
Example of thin from below. Photo A: Before thinning. Photo B: After thinning. Photos: Michelle Ensminger.

 

Ponderosa pine, western white pine and western larch all tend to be tall and self-prune (the natural removal of lower limbs that don’t receive enough sunlight to survive). Western white pine and western larch have lower volume crowns and carry their crowns well above surface fuels compared to true firs, Douglas-fir, western hemlock, and western redcedar. Because of these attributes, western white pine and western larch do not carry crown fires well and tend not to create ladder fuels (fuels in the lower canopy that carry fire up into the crowns of trees). In contrast, stands dominated by true firs, Douglas-fir, western hemlock, and/ or western redcedar do not self-prune well. They tend to carry large branches low in the canopy and have relatively voluminous crowns. Stands dominated by these species usually support crown fires.

Thinning cannot alter all variables that influence fire behavior, but it can influence factors such as species composition, available fuel, fuel arrangement, fuel moisture and surface winds. The objective of thinning in wildfire risk reduction is usually to prevent or slow the spread of crown fire by reducing surface and ladder fuels. Thinning also raises the height of overstory crowns and breaks up the connectedness of crowns, which reduces tree-to-tree spread of crown fires.

Wildlife management

Species associated with fairly open canopies and an open forest floor may benefit from thinning treatments. Thinning a stand of trees increases the amount of sunlight reaching the understory, which stimulates the growth of grasses, wildflowers and native shrubs. Elk, deer, and moose will likely benefit from the increase in forage quantity and quality. Small mammals such as chipmunks and deer mice may increase in number, particularly after thinning in Douglas-fir and ponderosa pine forests. This may be advantageous to species of hawks, owls and eagles that prey on small mammals in open forests and small clearings. Although not often considered as part of the wildlife community, pollinators such as moths and butterflies may also benefit from changes in structural diversity as a result of fuel reduction treatments that increase the amount of light reaching foliage and the forest floor.

Timber production

If you are managing your forested land for future timber production, thinning will be an important part of your management plan. Thinning releases resources to the residual trees allowing them to allocate to their fifth priority, diameter growth, which leads to an increase in tree volume. This increase in diameter growth results in an increase in overall stand value.

Thinning techniques

The tools and methods by which thinning is implemented are quite varied, and can result in significantly different stand structures. The type of thinning you select may depend on your objectives and on individual stand characteristics, such as species composition.

When managing for forest health and fuel reduction, private landowners typically use the “thin from below” method. Thinning from below consists of removing trees from the lower canopy, leaving larger trees to occupy the site. This method mimics mortality caused by competition or surface fires and concentrates available resources on larger, healthier, fire-adapted trees, while removing the stagnant, unhealthy trees.

Thinning is best accomplished in the late summer and early fall if possible. At this time trees will be least susceptible to damage from the thinning operation and the populations of insects that may be attracted to the slash created will be low. Winter also is an acceptable time to thin, but can lead to soil compaction and erosion if done at the wrong time. Thinning in spring and summer is not recommended as it can attract insects such as bark beetles and can affect wildlife, particularly nestlings.

For more information about thinning your property, please visit the Forest Stewardship Program and the Landowner Assistance Center pages on the Washington State Department of Natural Resources website.

By Melissa Fischer, Forest Health Specialist, DNR Northeast Region, Washington State Department of Natural Resources

 

Resources to  learn more:

Fettig, C.J., Klepzig, K.D., Billings, R.F., Munson, A.S., Nebeker, T.E., Negron, J.F., and Nowak, J.T. 2007. The effectiveness of vegetation management practices for prevention and control of bark beetle infestations in coniferous forests of the western and southern United States. Forest Ecology and Management. 238: 24-53.

Graham, R.T., Harvey, A.E., Jain, T.B. and Tonn, J.R. 1999. The effects of thinning and similar stand treatments on fire behavior in western forests. U.S. Forest Service, Pacific Northwest Research Station. PNW-GTR-463.

Pilliod, D.S., Bull, E.L., Hayes, J.L. and Wales, B.C. 2006. Wildlife and invertebrate response to fuel reduction treatments in dry coniferous forests of the western United States: A synthesis. U.S. Forest Service, Rocky Mountain Research Station. RMRS-GTR-173.

How to Make a Wildlife Tree

PoemsAh, trees. Those leafy icons of life and nature, inspiring writers through the ages…

Douglas squirrel.
Wildlife tree dweller: Douglas squirrel. Photo: Ken Bevis.

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

Excellent-natural-wildlife-tree-crop
This excellent natural wildlife tree features numerous cavities wildlife. Photo: Ken Bevis.

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, wildlife tree creation pioneer.
Tim Brown, wildlife tree creation pioneer. Photo: Kelsey Ketcheson.

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

Farrell-McWorter Park
A wildlife tree in Farrell McWorter Park in Redmond, Washington, created over 30 years ago and now used by many types of wildlife. Photo: Ken Bevis.

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.

jagged-top
LEFT: Tim Brown uses a chainsaw to make a jagged top in topped tree. RIGHT: Example of jagged top created with chainsaw cuts and hammer blows. Photos: Ken Bevis.

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.

before-after
Wildlife habitat tree demonstration site before (left) and after (right) treatment of trees.

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 Browntimothykbrown@msn.com

Small Forest Landowners Needed to Help in Fisher Recovery

The Pacific fisher (Pekania pennanti) is one of the larger members of the weasel family and is only found in North America’s boreal and temperate forests. Through excessive trapping and habitat loss, fishers were eliminated from Washington state by the mid-1900s. The species is currently listed as endangered in the state of Washington and is under consideration for listing as threatened under the federal Endangered Species Act (ESA). This federal listing decision will be made in early April 2016.

Pacific fisher
Listed by the Washington Fish and Wildlife Commission as an endangered species, the Pacific fisher was reintroduced into the Olympic Peninsula in 2008. Photo: Pacific Southwest Region-USFS

The Washington Department of Fish and Wildlife (WDFW) has been working with the US Fish and Wildlife Service (USFWS), National Park Service, US Geological Survey and the US Forest Service to help recover the fisher. Recovery areas have been identified for the Olympic and Cascade ranges. Successful reintroductions occurred in Olympic National Park from 2008 to 2010, and reintroductions are now occurring in the South Cascades (Mount Rainier National Park and Gifford Pinchot National Forest). In two or three years, reintroductions will follow in the North Cascades (North Cascades National Park and Mt. Baker-Snoqualmie National Forest).

In addition to reintroducing the species, WDFW has also been preparing for the potential federal listing by developing a voluntary conservation approach for private landowners – a Candidate Conservation Agreement with Assurances (CCAA).

Simply stated, those who agree to take certain measures to protect fishers would not be subject to future land-use restrictions that might result if the species is listed under the ESA.

fishers_factsheet-final020216-002
Fisher recovery areas in Washington state. Source: Washington Department of Fish and Wildlife.

How Can Forest Landowners Help?

Wildlife managers are seeking help from forest landowners to work as partners in the recovery of fishers in Washington State. Forest landowners can qualify for this type of conservation agreement by voluntarily signing on to the CCAA administered by WDFW. Proposed conservation measures applicable to all enrollees include:

  • Allowing WDFW access to your property to monitor fishers and their den sites.
  • Providing protection to denning females and their young by avoiding disturbance around known denning sites while occupied (generally between the months of March and September).

The draft CCAA is currently going through the federal review and approval process, which includes a 30-day comment period. Once approved, landowners can voluntarily sign on to the CCAA until such time as fishers become listed under the federal ESA. In order for landowners to take advantage of this opportunity, they must be signed on to the CCAA prior to listing (which could be early April of this year (2016)).

Species Information

The species is dark brown and has a long bushy tail, short rounded ears, short legs, and a low-to-the-ground appearance. Fishers mate from late March to early May, with females giving birth to a litter of one to four kits the following year. While birthing dens are always in cavities of live trees, females may move the kits to other den structures, including cavities in snags or downed logs, or to log piles or ground burrows. Fishers prey on small mammals such as deer mice, voles, and squirrels throughout their 25- to 50-mile home ranges.

They prefer low- and mid-elevation forests with moderate to dense canopy closure and an abundance of large woody structures such as cavity trees, snags, and downed logs.

For more information on the fisher, the CCAA and enrolling in the program, please contact Gary Bell by phone at 360-902-2412 or via email at Gary.Bell@dfw.wa.gov

Please respond before April to ensure you are included in the CCAA prior to possible listing.

Nest Boxes: A Functional Habitat Enhancement

The jaunty woodpeckers rock side to side as they chisel into dead trees carving homes and seeking bugs. We hear their hearty “Ha Di Da Ha Ha. Ha Di Da Ha Ha” and are amazed at their rhythmic drumming in the spring. They are keystone species in the forest, eating lots of insects and providing habitat for other species through their activities.

Many of our fantastic forest wildlife species require cavity habitats in dead wood for reproduction and roosting cover. Over the years, however, human activities have often removed this critical habitat component. The importance of this habitat feature is now common knowledge among foresters, biologists, managers and landowners, but, recruitment and development of dead wood structure with suitable softness (from fungal action) for cavity excavation by woodpeckers, can take many years. Thus, action is sometimes needed to provide cavity habitats now.

NB_swallow on box
Providing adequate numbers of snags, standing dead trees is, of course, the best strategy, but sometimes, they simply don’t exist. Substitute cavities can be provided through creative carpentry, utilizing man-made slices of trees (boards, that is) to manufacture artificial, quasi-cavities we call “nest boxes”. (The term “bird house” is incorrect, as it implies the box will provide all of life’s requirements for the species; nope, these boxes are for nesting and, sometimes, roosting.)

Cavity Excavating Birds Come in Many Sizes

Cavity excavating birds in the Pacific Northwest come in a variety of sizes, from the massive pileated (wingspan 29”, weight 290 g) to the diminutive red breasted nuthatch (wingspan 8”, weight 10 g). Each species creates cavities that roughly match the size of the bird, and precisely provide the depth and width to enable brood rearing. Some of these attributes help with thermal regulation for the helpless young, provide room for them to grow and stretch out, and depth to resist the inevitable predators that will try to consume the delicious eggs and young. For example, flickers are about 12 inches long, and make cavities with entrance holes about 3 inches in diameter and 13 to 16 inches deep. The entrance hole is proportional to the size of the bird, and the depth is enough to keep predators from easily reaching the brood. Pileateds make appropriately enormous cavities!

Constructing cavities is a regular part of nesting and courtship behavior among the woodpeckers and the other smaller cavity excavating birds (chickadees, nuthatches). These birds will make a new cavity in most nesting seasons, and abandon the old ones when nesting is done. These abandoned cavities are prime real estate and readily sought after by a host of other species, the secondary cavity nesters. These species include many of our favorites, and will readily use man made nest boxes.NB_squirrel

Building a Nest Box

In the north Cascades town of Twisp, Washington, Patrick Hannigan has a unique business creating species-appropriate, biologically correct nest boxes out of salvaged wood from construction sites or demolitions.

“I always loved building things”, said Hannigan when I interviewed him, “and I am fascinated by birds. Construction projects always leave huge piles of scraps, and this is my way of returning this waste back into habitat.”

Patrick, who has supplied hundreds of the boxes to clients across Washington, adds:

“The species I have had use them the most include kestrels, Western bluebirds, tree and violet green swallows, saw whet owls, both mountain and black-capped chickadees, red breasted and white breasted nuthatches and wrens.”

I asked what are key elements for functional nest boxes? He listed five:

  1. Proper dimensions: that is, entrance hole size, depth to floor, and floor dimensions
  2. Proper ventilation: ¼-inch slot or holes along the top
  3. Drainage in floor to allow water out and air in to dry nesting material
  4. Door that opens to facilitate easy clean out. It is best if no tools are required for this job.
  5. Roughened interior walls to help fledglings climb out. Sometimes boxes made of smooth, planed wood become an inadvertent death trap for baby birds.

Three sizes of nest boxes are all that most small forest landowners need to consider.

  • Small: A 1 1/8” entrance hole, with a 4 ¼” square floor is just right for chickadees and wrens.
  • Medium: Swallows and bluebirds need 1 ½” entrance holes and a 5” x 5” minimum floor.
  • Large: Kestrels, small owls and squirrels need 4” holes and 17” to the bottom of the box. (Many nest box plans are available online, so check these before designing one on your own).

These three sizes will cover most of the species you may encounter on your lands (Wood duck boxes that would be placed along ponds and wetlands are larger and a special case).

Materials: Dos and Don’ts

Nest box materials can be any type of wood, but roofs need to be sturdy (and perhaps waterproofed). Avoid particle board as it will crumble in a short time. Pine and fir work fine. Do not paint on the inside of the box but the birds don’t care if the outside is painted.

Hannigan also cautions against using metal roofs or sides. These can become “bird microwaves” and when the weather warms can have the unintended consequence of killing the same birds the structure was meant to help. And ornamental “bird houses” with random hole sizes or inadequate interiors, made to be cute and not functional (sorry to those clever crafty folks!); bad bad bad. “These are made for people, not birds and can even be harmful.”

Placing Nest Boxes

Hannigan recommends focusing on forest edges for the most nesting opportunities. As to placement, think vertical. Small birds will be lower in the canopy, larger species prefer to be higher. Smaller boxes can be placed at eye level, where they are easy to clean out. Place larger boxes for owls or kestrels at least 12 to 15 feet high, a comfortable height using a standard ladder. Make sure the entrance has a clear flight line not too encumbered by overhanging branches. NB_lostLake-OKcountyHannigan recommends placing your first boxes where they are near your home, in normal sight lines so you can see and appreciate what species are using them. Boxes can be placed close together for swallows, or spread around for other species. See if they are being used in a given season and move them if they are not.

Caution should be noted with bluebird style or kestrel boxes near human habitation. These can provide habitat for aggressive starlings or house sparrows. In normal forest settings, however, these species are rarely a problem.

Nest boxes are one of my favorite tools for enhancing habitat on forest lands. Why? Because they work, they are something we can DO, and we get to experience firsthand some of the wonderful wildlife in our forests. Nest boxes are an excellent tool to help small forest landowners provide habitat for the many wildlife species we value so much; but, as with any tool, they need to be applied properly, with careful construction and placement.

Please contact me with questions, comments, pictures or stories about your nest boxes.

By Ken Bevis, DNR Stewardship Wildlife Biologist, ken.bevis@dnr.wa.gov 

Tree Stems are Wood… and Habitat

Tree stems majestically hold up the forest canopy and lead our eyes into the sky. The leafy ceiling above gives us comfort supported by those massive woody cylinders.

What about those stems? Forest products are generally considered lumber, partitioned slices of tree stems that are cut to specification and put together into homes, furniture and a zillion other practical uses. Wood provides considerable human habitat. Wood in the forest ecosystem has significant value as wildlife habitat, too.

What is a Tree?

That marvelous living thing that we call a “tree” is mostly, actually dead. The marvelous collective functions of the tree, photosynthesis, conduction of water and nutrients, growth and simple physical support, all add up to “tree”. But is it all “alive”?

Life by definition means cell division and respiration. The only parts of a tree that are truly alive in the biological sense are the cambium layer, root tips and the living parts of the leaves. That’s it. Most of a tree, wood, was once alive, but now functions as tubes for the movement of water up and nutrients down, and support tissue for the photosynthetic surfaces reaching up to compete for sunlight.

Wood is dead tissue. Mostly cellulose, hard to digest for most organisms, but great structure for wildlife habitat; especially after the living defenses of the tree are gone. Once the tree dies, the habitat value of wood takes off.

Multiple pileated woodpecker cavities in a larch snag
Multiple pileated woodpecker cavities in a larch snag in northeast Washington. After more than 35 years as a snag, the tree fell in 2015. Photo: Ken Bevis/DNR.

Remember the three primary needs of wildlife; food, water, cover? Dead wood providers food in the form of insects living in the dead wood, and cover in the form of cavities, crevices or loose bark.

The inside of a tree stem is usually unavailable habitat until primary cavity excavators (woodpeckers) make their nest cavities in the dead stems. Shazam! Suddenly, the inside of a tree stem is cover. And a really great place to rest and raise young.

Approximately 40 percent of forest wildlife species use dead wood for some portion of their life cycle. The list is long. A few of the species that use standing dead trees, or snags, are:

  • Pileated woodpecker
  • Hairy woodpecker
  • Downy woodpecker
  • Red-naped sapsucker
  • Douglas squirrel
  • Marten
  • Long-tailed weasel
  • Chipmunks
  • Flying squirrel
  • Bats
Pleated woodpecker.
Pileated woodpecker. Photo: Glenn Thompson.

Woodpeckers will make new cavities every year, or improve old ones, as a regular part of courtship and nesting behavior. These cavities in dead tree stems are prime real estate. Fledging rates (babies to adulthood) for cavity nesting birds are much higher than rates for ground or cup nesters. Non migratory species (such as the pileated woodpecker) will use cavities for roosting in the non-breeding season. Small birds such as nuthatches will sometimes communally roost in cavities together. Flying squirrels are known to cuddle through cold winter days (they are nocturnal) piled into cavities. Cavities in dead tree stems are some of the best cover available in forest habitats, and are limiting factors for the presence or absence of many species.

When a tree falls and becomes a log, habitat value continues. The log acts in a similar way as a standing dead tree, providing food in the form of insects and fungi. Cover too, particularly in the interstitial spaces provided between layers of rotting wood. Wildlife use of logs is extensive, (and the subject of a future article). For example, many salamanders spend the dry seasons inside of logs, where conditions stay moist all year. Small mammals such as forest mice and voles live in and around rotting logs. Rotting wood feeds the soil with organic matter and nutrients.

Habitat log near Forks, Washington.
Habitat log, down for many decades, near Forks, Washington. Note the many cracks and soft, moist rotting wood.

 

 

 

 

 

 

 

 

 

 

Trees provide many habitat functions in the forest. Ironically, once they die, much of their habitat value to forest wildlife species increases. Snags and logs can last many, many years. Attentive landowners know of old dead trees on their property, and value them for the habitat they provide. These dead trees add character, beauty and habitat value to forest land.

Mature living trees present habitat on the surface of the stems. These barky surfaces are good foraging habitat for some species. Small birds, such as brown creepers, glean the tree surfaces for spiders and other insects hiding in the cracks. Dead branches can harbor insects too, and small birds such as chickadees can use these pieces of attached dead wood as important foraging areas.

Forestry activities tend to manage trees for maximum growth, thus producing many live, solid stems. Thinning activities enhances this growth and produce much live tree surface. Deliberate attention to maintenance, and even creation, of dead wood habitat structures can provide significant benefit to wildlife populations.

Wood. It is habitat.

By Ken Bevis, DNR Landowner Assistance Wildlife Biologist

For more information or to schedule a free site visit to your forest land, contact Ken at: Ken.Bevis@dnr.wa.gov