Forestland Grazing in the Inland Northwest

Many of the cultural practices that family forest owners use to improve forest production may be used to improve other components of their forestland. Forest owners may wish to increase production of grasses and forbs for livestock production and/ or wildlife habitat improvement. Forestland grazing presents opportunities to increase land productivity, improve cash flow, and to increase the diversity of plants and wildlife – all of which are not mutually exclusive. Most forestland grazing is found on the east side of the Cascade Mountains, as forest stocking levels tend to favor more open stand conditions. While generally discouraged by foresters due to soil impacts on water-saturated soils, limited forestland grazing is found on the west side of the Cascades, and generally on sites that are managed to promote more open stands.

PHOTO: T. Hudson, WSU
Photo: T. Hudson/WSU

Grazing can benefit forest management in several ways. For example, grazing and browsing can reduce the need for herbicides and mechanical weed control, and manure can reduce the need for fertilizer application by promoting nutrient recycling. Forest stands that include grazing as a management option are often park-like in appearance, and generally more socially acceptable than traditional plantations managed exclusively for timber. Low-intensity cattle grazing-grazing reduces competition for moisture between overstory trees and understory shrubs when the stand is very young. Studies in Oregon have shown up to 50 percent increase in forage and timber growth over 10 to 20 years with the integration of livestock into the system. Also, adding nitrogen-fixing vegetation such as legumes to the forage mix combined with recycled nutrients in dung and urine increases nitrogen uptake of trees on sites that are naturally deficient of nitrogen.

Weight gains for cattle on forested pastures may exceed those of grasslands because: (1) prolonged spring run-off provides more spring moisture to understory plants, (2) forage reaches maturity more slowly, (3) grasses are protected from sun and frost curing, and (4) forage species diversity provides a longer grazing season. Experience has shown that forests also protect cattle from weather – cutting the direct cold effect by 50 percent or more and reducing wind velocity by as much as 70 percent. Cattle protected by windbreaks gained 35 lbs. more than unprotected herds during a mild winter and lost 10.5 lbs. less during severe winters. Weight gains also improve with proximity to shade.

Livestock grazing in forests is much more common than many people realize. In a recent survey, 26 percent of Washington family forest owners reported livestock grazing on their forestland in the previous 12 months. Nationally, livestock graze about 25 percent of all forests. This forest area accounts for about 13 percent of the total land grazed in the U.S. and roughly equals the total area of improved pastures and grazed croplands, combined.

Foresters often discourage livestock grazing in timber plantations for fear that trees will be browsed, debarked, or stepped on. Once reassured that the plantations can be safely grazed without damaging trees, the next silvicultural concern is often soil compaction. Cattle, sheep, goats and other livestock can exert as much downward pressure on soil as do agricultural tractors and unloaded forestry harvest equipment. When a sustainable number of animals are managed, trampling only occurs over a limited area. In addition, soil compaction by livestock is generally confined to the top few inches of soil whereas heavy equipment can compact to depths over a foot. Extensive reviews of published literature found that grazing does compact soil—though it is unusual for livestock grazing on drained soils to sufficiently compact soils to hinder plant growth. Forested rangelands in the western U.S. are most frequently used as summer-fall range, when soils are not saturated. It is unlikely that responsible forest grazing will sufficiently compact soils to reduce tree growth unless soils are poorly drained.

Photo courtesy of Cornell University
Photo courtesy of Cornell University

Large seedlings are cost-effective in forest grazing systems. While more difficult and expensive to plant, these trees have a higher tolerance to damage from livestock and will more quickly escape the maximum height of browsing by livestock and deer. Careful management should be the norm when grazing young stands, particularly on steep slopes to see that soil is not displaced by animal hoof action. The number of trees to plant and the planting pattern vary widely with the objectives of forestland grazing. If the forest component is to be emphasized, stocking of 200 to 400 trees/ acre are common, with grazing restricted to the first decade or so after tree planting. If grazing is to be maintained over the long-term, lower tree stockings will be needed to maintain forage production with subsequent overstory tree thinning that reduces stocking to as few as 50 trees/ acre at maturity. Tree pattern becomes increasingly important as density increases. Conventional forests use rectangular grids of trees to minimize competition between trees at the expense of the understory vegetation. Square grids, single, double or triple rows, and cluster plantings have all been used in grazed forests. The grid layouts optimize the area for tree growth, while the row or cluster plantings share the site resources more evenly with the forage crop. Rows support greater understory forage and the ease of access to row plantings for agricultural operations such as fencing, fertilizing, haying, etc., make them popular with producers.

Deer photo by E. Gutierrez/WSU
Photo: E. Gutierrez/WSU

Overgrazing can lead to the removal of terminal leaders, substantial lateral branch defoliation and, more rarely, debarking. Young conifers are fairly tolerant to defoliation provided that the terminal leader is left intact. Research applicable to eastern Washington forests reported that heavy lateral branch defoliation of 4-year-old Douglas-fir did not affect tree height and reduced the current year’s growth by only 1.5 percent compared to undefoliated trees. It takes browsing of over half of the needles produced in the current year or girdling of over half of the stem to visibly reduce long-term growth. Removal of terminal leaders is a more serious matter. Loss of conifer terminal leaders not only forgoes that year’s height growth, it may also reduce diameter growth by as much as 30 percent. The risk of growth loss and tree deformation of young conifers in pastures is high enough to warrant either careful monitoring of forage availability and livestock grazing behavior, or physical protection of the trees during the first few years after plantation establishment. Given the increased competition from other trees and understory shrubbery on west side Cascade forests, the loss of a year’s height growth may eventually result in competition mortality. However, to place these concerns in perspective, studies in western Oregon forests report that native deer inflict more damage to young forests than livestock.

While livestock can graze new plantations safely, great care should be exercised when tree terminal leaders are within the reach of livestock. Pastures can be grazed during the spring growing period with negligible defoliation of trees provided that total utilization of forage does not exceed 35 percent of current seasons forage crop.

Tree damaged by deer.
Tree damaged by deer browsing. Photo: A. Perleberg/WSU

The potential for tree damage by livestock appear to be related to several factors including season of year (spring/ early summer is when other forage plants are most palatable, but compaction may be an issue), percent utilization of forage available, age of animal, and tree heights. One study in southern Oregon comparing tree seedling growth by cattle grazing in a recently planted pine plantation versus a non-grazed plantation, experienced enhanced tree growth due to both the reduced grass and shrub vegetation competition the with the pine seedlings as well as the nitrogen inputs from manure. Damage is more likely during the first two-three years of tree growth before resinous chemical defenses are well developed. After three years, conifer foliage is not particularly palatable to cattle or elk, though sheep, goats, and deer might still be attracted. Conifer foliage is most likely to be grazed in the spring when it is newly-emerged and the anti-herbivory defense compounds have not yet fully accumulated, or any time that livestock are short of other forage, however, livestock will consume conifer foliage in low amounts even when other preferred forage is available. This very low level of tree browsing often changes quickly info substantial levels as other forage is depleted. It is not unusual for over 90 percent of tree defoliation to occur when other forage choices are limited. Livestock grazing young forests must be checked frequently and animals properly removed when forage is depleted and they begin to actively feed upon trees.

Minimizing Livestock Damage

In general, livestock breed is not a useful predictor of damaging feeding behavior as is age, sex, and past experience of animals. However, larger breeds such as Charolais, Semmental; Gelbvieh, and Limousin tend to distribute less than smaller breeds, so concentration in areas such as riparian forests can become an issue with their tendency to linger that can lead over-grazing and potential damage to soil structure. Older dry ewes do far less damage to trees than young lambs or rams. Cattle, sheep and goats that have consumed either green foliage or dry needles regularly in the past are much more likely to feed upon young trees in pastures. In every flock or herd there are individuals that seem to be predisposed to feed upon trees. Feeding behavior may be taught to others. Tree damagers should be culled as soon as they are identified. Some practitioners also report that livestock transported into grazed forests from non-forested areas will browse young trees as a “novel” food. Fencing, tubing, repellents and livestock exclusion have all been used to control browse damage by both wildlife and livestock in grazed forests. Fencing works well when trees are concentrated in closely spaced rows to maximize grazing area and minimize fencing costs. Fencing can be permanent where continuous grazing is planned or wildlife damage to trees is a concern. Portable electric fencing has been successfully used for short time periods and prescriptive grazing to reduce invasive plants. Lightweight portable fencing is erected quickly when and where needed to protect trees from livestock, so monitoring of the grazing progress is not as critical as with open grazing. Protecting individual seedling trees with plastic mesh or rigid tubes has also been used successfully, but this measure has drawbacks. Cattle trampling and tube removal by sheep and subsequent browsing of the unprotected tree is a real concern, so monitoring of the grazing is required. Attaching the tube firmly is another problem. Rigid wood stakes often break when rubbed by livestock. Resilient materials such as bamboo are more resistant to breakage.

Riparian Area Concerns

Livestock grazing becomes more complicated where riparian systems are involved. Because riparian areas remain lush and green into the summer dormancy period for upland grasses and forbs, livestock will congregate in these areas for shade, water, and forage. This situation could result in overgrazing of riparian plants critical for riparian and stream function and physical damage of stream banks. Some rules of thumb include:

  • Allowing continuous, season-long grazing will damage riparian function.
  • Expect that in years of good rainfall, an early growing season for grazing vegetation will encourage cattle to graze uplands, where green forage and warm temperatures are more favorable.
  • Install off-stream water and salt far away from riparian areas.
  • Cull animals that prefer to “camp” in riparian areas.
  • Force cattle out of riparian areas with riders or substitute with herded sheep or goats.
  • Exclude riparian grazing until late in the growing season, but be careful to watch for overuse of woody plants.
  • Expect mixed or very site-specific results for riparian pastures in rotation systems.
  • A number of successes have been observed when late winter and early growing season grazing systems were merged, but be careful to monitor compaction.
Cattle grazing in riparian area
Cattle grazing in riparian area. Photo: T. Hudson/WSU

Conclusion

Livestock management is the key to successful forestland grazing. Important considerations for proper grazing management include where the livestock graze, season of use (timing), length of use (time), and the amount of plants grazed (intensity). Some rules of thumb include:

  • Match the type of livestock to the forage base.
  • Make judicious use of fencing, salting, off-riparian water, and trails to aid proper distribution and minimize damage.
  • Customize rotational grazing systems to the local area and manage them intensively; time and timing will vary depending on the location, year and objectives.
  • Move livestock well before browsing begins on trees.

 

By Andrew B. Perleberg, Regional Extension Specialist – Forestry, Washington State University and James P. Dobrowolski, Rangeland, Grassland, and Water Quantity National Program Leader, National Institute of Food and Agriculture, USDA.

Potential for Douglas-fir Beetle Outbreaks in Eastern Washington

Douglas fir killed by bark beetle
Beetle damage in stand of Douglas fir. Photo: Kenneth E. Gibson, USDA Forest Service, Bugwood.org

Several windthrow events in 2015 have paved the way for a potential outbreak of Douglas-fir beetle in areas of eastern Washington this spring (2017).

Douglas-fir beetle egg and larval tunnels
Characteristic pattern of Douglas-fir beetle egg and larval tunnels. Photo courtesy of Oregon Department of Forestry.

The Douglas-fir beetle is a bark beetle that normally breeds in felled, injured, windthrown or root-diseased Douglas-fir. It may also attack western larch, but can only produce brood in downed trees. At outbreak levels, this bark beetle can attack and kill large diameter, healthy Douglas-fir. Outbreaks tend to occur after extensive windthrow events such as was seen in 2015. Outbreaks may also occur after defoliation events, fire and extended drought. Dense stands surrounding areas where windthrow, defoliation, fire and drought events have occurred may be at high risk for an outbreak, particularly if those stands contain a 50 percent or more component of Douglas-fir that are greater than 120 years of age and larger than 14 inches DBH (DBH = diameter at breast height; diameter of a tree bole 4.5 feet from the base).

The Douglas-fir beetle has one generation a year. Brood that developed through 2016 will pupate and emerge as adults this spring. Once emerged, they will begin attacking standing trees surrounding the windthrow, as the windthow is no longer habitable for them.

What can be done?

The best approach to prevent an outbreak this spring is to salvage any large diameter Douglas-fir or western larch that were downed by the storms prior to the adult beetle flight, which should occur in April, depending on temperatures. Windthrown trees can also be burned or chipped on site if salvage is not an option. Time is running out; if you find you cannot take care of this material, the use of the anti-aggregate pheromone MCH is another option.

A pheromone is a chemical released by bark beetles that is used to affect the behavior of other beetles of the same species. Aggregating pheromones attract beetles, while anti-aggregates repel them. A bark beetle might use an anti-aggregate to prevent overcrowding within a tree. An anti-aggregate basically tells other beetles that there is no room for additional inhabitants in the tree.

MCH bubble capsule stapled to a tree
MCH bubble capsule stapled to a tree. Photo: US Forest Service.

The Douglas fir-beetle naturally produces an anti-aggregate to repel others. A synthetic version of this anti-aggregate, MCH, has been produced and is available for purchase through several online companies. MCH comes in a “bubble capsule” and can be used to protect individual live, high-value Douglas-fir or even an entire stand. For individual tree protection, two bubble capsules can be stapled on either side of a Douglas-fir bole at approximately 6-8 feet from the ground for a tree less than 24 inches DBH. Four bubble capsules should be used for Douglas-fir larger than 24 inches DBH. To protect a stand of Douglas-fir, 30 bubble caps per acre can be evenly placed through the stand.

MCH costs approximately $2.50 per capsule and should be hung prior to the beetle flight in April. It is advisable to contact your local forest health specialist if you are considering this method of management. Additional information about this method can be found in the free publication, “Using MCH to protect trees and stands from Douglas-fir beetle infestation,” published by the US Forest Service.

By Melissa Joy Fischer, forest health specialist, Washington State Department of Natural Resources, melissa.fischer@dnr.wa.gov

 

I Hear Bugs Chewing the Wood Inside my Trees!

ugphotos1-3
TOP: Figure 1. Example of a longhorned beetle: spotted pine sawyer (Monochamus clamator) Photo: Richard C. Hoyer, Bugguide.net MIDDLE: Example of a metallic wood borer: Golden Buprestid (Buprestis aurulenta) Photo: Melissa Fischer/DNR BOTTOM: Figure 3. Example of a woodwasp: Sirex nigricornis Photo: Schiff et al. 2006

I hear bugs chewing the wood inside my trees!

Many land managers have contacted me in a panic saying that they could hear bark beetles feeding in their trees. Although bark beetles may be present in those trees what they were likely hearing is wood borer activity. Wood borers tend to be much larger than bark beetles and are, therefore, more likely to be heard chewing away inside trees.

While bark beetles feed solely on a tree’s phloem, wood borers feed on sapwood and heartwood as well as phloem. Native wood borers attack stressed, dying, or dead trees; there are very few native species that actually kill trees.

Wood borers are attracted to volatile gases released by dead or dying trees and lay their eggs under the bark of these trees. Once the larvae hatch, they begin feeding on the inner bark and then tunnel into the wood. The larvae are white, legless grubs and can be quite large. They are valued as a food source by woodpeckers (they make great fishing bait too!) and woodpecker activity is often seen on trees that contain wood borers. The tunnels produced by larval feeding activity have a random pattern and increase in size as the larvae grow.

Frass (beetle poop) is likely to be present within the tunnels. Unlike bark beetle frass, which is fine and reddish in coloration, wood borer frass tends to look more like shredded wheat and is white in color. When wood borers develop into adults, they emerge from trees and leave exit holes that are typically quite a bit larger than those left by bark beetles.

Wood borers play an important ecological role by introducing wood decaying organisms into dead and dying trees which, in turn, helps to speed nutrient cycling. Typically, no management is necessary for native wood borers in a forested setting. Wood borers can damage lumber, but damage is unlikely to occur if the wood has been treated.

Types of Wood Borers

bugphotos4-6
TOP: Figure 4. Asian longhorned beetle Photo: Joe Boggs, Bugwood.org MIDDLE: Figure 5. Citrus longhorned beetle Photo: Art Wagner/Forestry Images. BOTTOM: Figure 6. Emerald ash borer. Photo: Marianne Prue/Bugwood.org

There are three common wood borer families; Cerambycidae, Buprestidae, and Siricidae. The family Cerambycidae, often called longhorned beetles (adults) or roundheaded wood borers (larvae), includes many species. Adults can range in size from ¼ to 2 ½ inches in length. Adults, particularly the males, have long antennae, hence the name longhorned beetle (Figure 1).

The family Buprestidae are commonly known as metallic (adults) or flatheaded (larvae) wood borers. Similar to longhorned beetles, there are many species, and adults may be ¼ to 2 ½ inches in length. Metallic wood borers have small antennae and some are very beautiful, with iridescent or metallic coloration somewhere on the body (Figure 2).

Flatheaded woodborer larvae can be differentiated from roundheaded wood borer larvae in they have a flattened and broadened area beneath the head (thorax) that gives the appearance of a flat head. Rather than the round exit holes left by roundheaded wood borers, flatheaded wood borers leave D-shaped exit holes.

The family Siricidae, often called woodwasps or horntails, are in the order Hymenoptera (i.e., wasps), unlike Cerambycidae and Buprestidae which are in the order Coleoptera (i.e., beetles). Adults may be ½ to 1 ½ inches in length and have a short hornlike process at the end of their bodies. Females have an additional stinger-like ovipositor which is used to oviposit eggs under the bark of trees (Figure 3).

Woodwasp adults can be distinguished from common wasps in that they have thick waists and neither males nor females can actually sting. Woodwasp larvae look similar to roundheaded wood borers but have a small spine at the end of the body. Woodwasps are particularly attracted to fire damaged trees and all except one western species feeds on conifers.

Although native wood borers typically attack stressed, dying and dead trees, several invasive species have been introduced into the United States that are incredibly damaging. The Asian longhorned borer (Anoplophora glabripennis) was introduced into the eastern United States in the early 1990’s. The Asian longhorned beetle feeds on many deciduous species (birch, horse chestnut, poplar, willow, elm and ash), but maples are one of its favorites.

This species has killed thousands of trees in New York and Chicago. Adults are large, 1 to 1 ½ inches long, and have wings that are shining black with irregular splotches of white. The antennae have bands of black and gray and the feet and legs have slate-blue “hairs” (Figure 4). This species can be confused with another invasive, the citrus longhorned beetle (Anoplophora chinensis, Figure 5).

bugphotos7-8
TOP: Figure 7. The native Prasinalia cuneata. Photo: William Ericson, Bugguide.net. BOTTOM: Figure 8. Sirex woodwasp (Sirex noctilio) female on the left and male on the right. Photo: http://www.sciencephoto.com

The emerald ash borer (Agrilus planipennis) is an invasive metallic-green wood borer (Figure 6) currently found in 30 states. The emerald ash borer attacks ash trees and has killed hundreds of millions of ash in North America. If you have seen rectangular purple traps hanging in trees alongside the road, these traps are being used to monitor for the emerald ash borer, which is attracted to this particular color. The emerald ash borer may be confused with many native metallic wood borer species, such as Prasinalia cuneata (Figure 7).

The European woodwasp (Sirex noctilio, Figure 8) has been accidently introduced into the eastern U.S. as well. This species attacks and kills living pines. Similar to the emerald ash borer, this species may be easily confused with native species.

Reports from citizens help scientists track the spread of these pests. To report a potential invasive species in Washington state, take a picture if possible, and contact the Washington Invasive Species Council.

By Melissa Fischer, DNR landowner assistance/stewardship forester, melissa.fischer@dnr.wa.gov 

References:

That Darn “Brush” (a New Look at Our Wonderful Forest Understory Habitat)

Black hawthorn (Crataegus douglasii).
While considered a nuisance by many landowners, shrub growth like black hawthorn (Crataegus douglasii) provides important shelter and forage for many many wildlife species.

Stand in your forest and count the overstory tree species you see. On the west side, this will likely include Douglas fir, hemlock, cedar and alder. On the east side, you are likely to tally Douglas fir, ponderosa pine and grand fir. Now, from that exact spot, count the shrubby understory, (or “brush”) species that you. This may include oceanspray, serviceberry, ninebark, salal, salmonberry, red or blue elderberry, cascara, beaked hazelnut, bitter cherry, chokecherry, evergreen huckleberry and so on. Nearly always there are two to three times as many species of native shrub, understory species on a site than there are tall trees. Wow!

Trees generally have a single stem and reach the highest levels of the canopy, while shrubs have multiple stems and grow in the understory. And yes, sometimes there are plants that confuse us. This rich, and often overlooked and underappreciated, layer of our forests contains some of the best wildlife habitat out there.

Benefits of Brush

Nearly 25 percent of our forest-dwelling wildlife rely on these plants for food or cover, and would not exist on our lands without these wonderfully dense thickets. Song sparrows, spotted towhee, warblers, chipmunks, deer and so. The critter list of those that thrive on this critical habitat element is long. In fact, the shrub layer may be the most important habitat feature for a high diversity of wildlife species in early forest successional stages. Systematic research in Oregon has shown that songbird abundance and diversity is increased when west side plantations are allowed to develop some shrub components.

When sunlight reaches the ground, even in small amounts, the various shrub species will take advantage of this niche and grow, sometimes for many years and to impressive mass. Who hasn’t seen a gap in the wet forest where the shrubs have come into create a little pocket of shrubs in the midst of an otherwise dark conifer overstory? These canopy gaps are a great source of habitat diversity. Mixed stands of mature trees, (conifer and hardwood), openings and substantial shrub components can provide some of the richest and most diverse habitats in our forests.

Many shrub species produce “mast,” or fruit, that is eaten by a wide array of wildlife, from birds to the smallest mammals and all the way up to the black bear. The wonderful flowers of our shrub species provide feeding opportunities for pollinators, including hundreds of species of native bees, hummingbirds and butterflies. Unlike the conifer, these flowers produce nectar, a rich draw for many animals including specialized insects. And most of our game species, those big charismatic megafauna, forage on these plants too. Shrubs usually carry these animals through the winter.

Superstars

There are many shrub (“brush”) superstars. Here we highlight just a few of our best wildlife habitat shrub species.

Blue elderberry (Sambucus-cerulea)
Blue elderberry (Sambucus-cerulea)

Blue elderberry (Sambucus cerulea): This lovely plant grows in sunny spots east and west of the Cascades. It can take on a fairly large form if given enough time and light, reaching up to 25 feet high and across. Multiple stems produce lush, compound foliage that is preferred browse for deer, elk and other animals. The abundant purple berries are favorites of many birds and seldom last long. These same berries can even be made into wine or jam. If you want to enhance wildlife habitat by planting shrubs, this one is a great choice.

Red elderberry (Sambucus raesmosa)
Red elderberry (Sambucus raesmosa)

Red elderberry (Sambucus raesmosa): Wetter sites in western Washington grow the red elderberry, a very similar plant to the blue, with a branching brushy form and red berries favored by many wildlife species. These grow in small openings and in the dappled understory of mixed forest stands. In my observation these two plants usually don’t occur in the same locations, but both are great wildlife habitat plants.

Salmonberry (Rubus spectabilis)
Salmonberry (Rubus spectabilis)

Salmonberry (Rubus spectabilis): Dominating many understories across western Washington is the ubiquitous salmonberry. This plant features dense woody stems that can create a jungle of dense vegetation — perfect places for birds and small mammals to seek shelter. The berries resemble salmon roe (hence the name) and are eaten by most everything, including people.

 

Indian plum (Oemleria cerasiformis)
Indian plum (Oemleria cerasiformis)

Indian plum (Oemleria cerasiformis): Perhaps the earliest blooming shrub species in western Washington is the gorgeous Indian plum. This rich understory species occurs on many moist forest sites, providing early foliage and flowers for native pollinators. They produce lovely, tiny purple fruits and never last long, being eaten at first chance by many birds and mammals. Watch for the white flowers in the first blush of spring.

Indian plum foliage

Black hawthorn (Crataegus douglasii): The spiny hawthorn creates dense cover for birds and a great place for mammals to hide and rest. The fruits (called “haws”) are also eaten by many species. It prefers sun, but will get by in dappled shade. This plant occurs on both sides of the mountains.

Other shrub superstars worth mentioning include serviceberry, mock orange, ceanothus, cascara, salal, willow, dogwood, and even devil’s club. Each of these has great wildlife structure and bears fruit.

Management

Sometimes the dense nature of shrub cover can prevent conifers from regenerating for many years, much to the frustration of those attempting to grow trees for harvest. Vast effort is made to eliminate this competition on lands dedicated to tree production, often by using aerial application of herbicides. This is hard on the shrub layer to say the least. The small landowner, however, usually has mixed objectives, wishing to provide quality wildlife habitat AND grow the next crop of trees. This can be accomplished by identifying the best wildlife shrub species growing on your property and actively maintaining them over time by allowing for space to grow these plants. Conifer competition can be dealt with by physically cutting the competing plants back, and/or strategically using herbicides on individual plants or clumps, thus allowing the conifers to get above the shrub layer and form a new canopy.

Sometimes individual plants are cared for. Planting can work if adequate care is made for each plant. Control competition and prevent browse on young plants. Desired shrubs that have become tall and “leggy” with extended stems and leaf and fruits out of reach of browsers, such as deer, can even be simply pruned back just as we might manage the bushes in our yards.

These are just a few thoughts and examples of the fabulous shrub species we encounter on our forest lands that are worth knowing and keeping on the landscape. Find out what shrubs you have on your place. Their value to wildlife as habitat is very great and definitely worth managing for.

Learn and enjoy your brush, or should I say, “shrub habitat.”

For more information or questions about managing small forest lands for wildlife, please contact me.

By Ken Bevis, DNR stewardship wildlife biologist, Ken.Bevis@dnr.wa.gov

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.