Managing Organic Debris for Forest Health Reconciling fire hazard, bark beetles, wildlife, and forest nutrition needs
Chris Schnepf, Russell T. Graham, Sandy Kegley, and Theresa B. Jain
PNW 609 A Pacific Northwest Extension Publication University of Idaho Oregon State University Washington State University Managing Organic Debris for Forest Health Reconciling fire hazard, bark beetles, wildlife, and forest nutrition needs
Chris Schnepf, Russell T. Graham, Sandy Kegley, and Theresa B. Jain
A Pacific Northwest Extension Publication University of Idaho Oregon State University Washington State University THE AUTHORS COVER PHOTO CHRIS SCHNEPF is an Extension Forester Forest organic debris is important for soil for the University of Idaho based in health. The main photo shows a log in the Coeur d’Alene. He provides educational process of decomposing and adding programs for forest owners, loggers, and structure to the soil. Thumbnail photos others interested in applied forest show organisms that will thrive in an area ecology and silviculture. with healthy forest soil and coarse woody debris: chanterelle mushroom, pileated DR. RUSSELL T. GRAHAM is a research woodpecker, and fisher. forester and silviculturist with the USDA Forest Service Rocky Mountain Research FUNDING Station in Moscow, Idaho. His research Partial funding for this publication was focuses on landscape processes and long- provided by the USDA Forest Service, term forest productivity concentrated on Northern Region State and Private Forestry. management of forest organic materials. ACKNOWLEDGMENTS SANDY KEGLEY is a forest entomologist Thanks to the following people who with the USDA Forest Service, Northern reviewed this publication and provided Region, Coeur d'Alene Field Office. Sandy many constructive comments: is involved in survey, detection, evaluation, Matt Abram, Logger, Hayden, Idaho prevention, and suppression of bark beetles and other major forest insects in northern Janean Creighton, Washington State Idaho and western Montana. University, Spokane DR. THERESA B. JAIN is a research forester Renee d’Aoust, forest owner, and silviculturist with the USDA Forest Clark Fork, Idaho Service Rocky Mountain Research Station Debbie Page-Dumroese, USFS Rocky in Moscow, Idaho. Mountain Research Station, Moscow, Idaho PUBLICATION ORDERING Steve Fitzgerald, Oregon State University Copies of this publication may be obtained from: Steve Funk, Forest Owner, Coeur d’Alene, Idaho UNIVERSITY OF IDAHO – Educational Communications, P.O. Box 442240, Moscow, Don Hull, Logging Safety Advisor, Idaho ID 83844-2240; tel: (208)885-7982; Logging Safety Bureau, Coeur d’Alene, Idaho e-mail: [email protected] Bill Lukens, Forest Owner, Sandpoint, Idaho OREGON STATE UNIVERSITY – Publication Ron Mahoney, University of Idaho, Moscow Orders, Extension and Station Communica- Ron Reuter, Oregon State University, Bend tions, 422 Kerr Administration, Corvallis, OR 97331-2119; tel: 541-737-2513 or Terry Shaw, Intermountain Forest Tree toll free: (800) 561-6719; Nutrition Cooperative, Moscow, Idaho e-mail: [email protected] WASHINGTON STATE UNIVERSITY – Extension Publications, Cooper Publications Building, P.O. Box 645912, Pullman, WA 99164-5912; tel: (509) 335-2857 or toll free: (800) 723-1763; © 2009 by University of Idaho. e-mail: [email protected] All rights reserved. Published 2009
2 CONTENTS
INTRODUCTION ...... 1 INLAND NORTHWEST FOREST SOILS ...... 3 Influence of fire on organic debris ...... 5 Organic debris & nutrients ...... 5 Organic debris & soil moisture ...... 9 Organic debris & soil structure ...... 9 Organic debris, roots, & mycorrhizal fungi ...... 9 MANAGEMENT OBJECTIVES FOR ORGANIC DEBRIS ...... 15 Fine organic debris (FOD) ...... 15 Coarse woody debris (CWD) ...... 15 STRATEGIES FOR MANAGING FIRE AND ORGANIC DEBRIS ...... 19 Fire hazard ...... 19 Methods to reduce fire hazard ...... 21 STRATEGIES FOR MANAGING BARK BEETLES AND ORGANIC DEBRIS ...... 35 Pine engraver beetle ...... 35 Douglas-fir beetle ...... 37 Spruce beetle ...... 37 Fir engraver beetle ...... 39 Generalizations about bark beetles and organic debris ...... 39 STRATEGIES FOR MANAGING WILDLIFE AND ORGANIC DEBRIS ...... 43 Snags ...... 43 Coarse woody debris size and characteristics ...... 45 Coarse woody debris arrangement ...... 47 How much coarse woody debris for wildlife? ...... 47 CONCLUSION ...... 48 APPENDIX: ORGANIC DEBRIS ESTIMATES ...... 50 Photo series ...... 50 Measuring Organic Debris ...... 50 REFERENCES ...... 58 PHOTO AND ILLUSTRATION CREDITS ...... 60 Figure 1. Removing organic debris is critical within 100 feet of homes and structures.
Figure 2. Poor soil means poor trees.
4 INTRODUCTION like mulch in a garden. It protects soil from excessive moisture loss, Forest organic debris includes recycles nutrients for trees and tree limbs, boles (trunks), needles, other forest plants, adds structure leaves, snags, and other dead and organic matter to the soil, organic materials. It ranges in reduces soil erosion, and provides amount and composition depending food and habitat for a wide variety on a forest’s history, tree species, of wildlife. condition, and age. In the Inland Many landowners are unclear on Northwest (Idaho, western how to reconcile the potentially Montana, eastern Oregon, and conflicting objectives related to eastern Washington) there is a lot forest organic debris. As a result, of discussion and concern about some landowners tend to remove removing organic debris from all organic debris while others may forests. treat as little as possible, to save Common reasons for removing money and time. organic debris include reducing This publication outlines the role bark beetle hazard, preparing a site of forest organic debris in Inland for tree planting, harvesting forest Northwest forests and provides gen- biomass for energy, and reducing eral management recommendations fire risk. For example, it is critical to maintain forest soil productivity to remove organic debris within 100 and improve wildlife habitat, while feet around homes and structures simultaneously reducing wildfire to reduce fire risk (fig. 1). And some and insect hazards. people simply like the aesthetics Many people refer to all branches of a forest with less organic debris and tops accumulated from logging -- loggers often speak with pride or a storm as “slash.” But different or admiration of “a good clean types of organic debris have differ- logging job.” ent functions and different All these issues are important. management challenges. To that But leaves, needles, and woody end, this publication differentiates debris left in a forest are not neces- between two broad categories of sarily wasted. A growing body of forest organic debris: fine organic research supports leaving some debris (FOD - material smaller than organic debris in forests (fig. 2). 3 inches in diameter) and coarse Organic debris left distributed woody debris (CWD - material 3 across the forest floor acts much inches in diameter and larger).
1 Figure 3. Forest soils are a living growth medium for trees and other organisms.
Figure 4. Surface organic layers can Figure 5. In frequently burned commonly be 1-2 inches deep on forests, organic layers can be thin. moist or cold forests.
2 INLAND NORTHWEST pole pine-subalpine forests to dry FOREST SOILS ponderosa pine forests. The most noticeable organic Soils are the foundation of forest component of forest soils are the growth and health. They provide surface organic layers. These “duff” structural support, nutrients, and layers usually consist of freshly water storage for trees and other fallen twigs, leaves, and needles. forest plants and fungi. Soil quality, In the middle of the surface layers, rainfall and temperatures determine there is usually a layer where plant how a forest regenerates, develops, and tree materials are being and functions. Over thousands of decomposed by insects, worms, years, climate and vegetation break fungi, bacteria, and other organisms. down or “weather” parent materials Below this, plant parts have (the bedrock and/or sediments decomposed to where they are not underlying a forest soil) into a unique distinguishable. mineral soil for a given forest site. These surface organic layers are Many Inland Northwest forest highly visible in a soil profile of soils have also been significantly moist forests and cold forests— influenced by wind-blown deposits often one or two inches deep of soil and volcanic ash. In addition (fig. 4). In dry forests and other to mineral contents, a large portion frequently burned forests, these of a soil’s volume is made up of pore layers can be very thin or even space, which helps a soil retain and nonexistent (fig. 5). However, where store moisture and allows for fire has been excluded from dry oxygen and carbon dioxide forests, large amounts of organic exchange around roots. materials can accumulate due to Organic materials from plants, very slow decomposition. This is animals, and fungi are also integral most apparent around the bases parts of a forest soil. These living of mature ponderosa pines that and dead organic components continually slough off bark and influence critical forest soil func- shed heavy amounts of needles. tions such as water holding, nutrient Varying amounts of wood from storage and release, aeration, decaying tree limbs and stems (also nitrogen fixation, bacterial and called boles, trunks, or logs) are fungal habitat, and protection from often mixed in the surface organic compaction and erosion (fig. 3). layers of forest soils (fig. 6). Rotten The contribution of organic debris wood (often brown and cubical) is to forests is as variable as the the most noticeable and longest- forests where it occurs. Inland lived organic material in forest soils, Northwest forests range from moist lasting up to centuries. Rotting cedar-hemlock forests to cold lodge-
3 Figure 6. Wood is often found mixed in organic Figure 7. Rotting wood can layers. also be found deeper in the soil profile.
Figure 9. Roughly half of a conifer’s above-ground nutrients are stored in the needles and branches. Figure 8. Stand replacing fires often left a great deal of coarse woody debris.
4 wood can also be found deeper in debris, but it would also kill some the soil. It can be created by trees, which would create snags that decaying tree roots or by logs would fall to the ground and replen- buried under sediment by soil ish some of the wood consumed in erosion after wildfires, or other soil previous fires. movement processes. In some cold In addition to fire, forest soil and moist forests, up to 40% of the organic material can also come top 12 inches of a forest soil can be from trees killed or damaged by composed of this buried rotten insects, disease, or winter snow wood (fig. 7). and ice storms, and from residues of forest management activities Influence of fire on organic debris such as thinning. Historically, wildfire helped determine the amount of fine and Organic debris & nutrients coarse woody debris in forests. Roughly half of a conifer’s Wildfires can be separated into two above-ground nutrients, such as broad classes. Stand replacing fires nitrogen and potassium, are stored killed nearly all of the trees. Surface in the needles, twigs, and small fires killed small trees and branches of the tree (fig. 9). vegetation in the understory but left Needles, limbs, and branches cycle overstory trees alive. Many individ- organic materials to the forest floor. ual fire events were a mixture of Deciduous trees and shrubs also these two types of fire (sometimes cycle large amounts of nutrients called mixed severity fires). each year. Stand replacing fires did not Moisture is the most limiting usually completely consume all factor to tree growth in most Inland wood on the site, particularly if Northwest forests. But inadequate intervening surface fires reduced nutrients limit growth as well. understory vegetation and fine fuels. Adding nutrients through fertiliza- Stand replacing fires typically tion increases tree growth on most moved through a site fairly quickly, Inland Northwest forests. Fertilizers burning up the needles and fine containing nitrogen, potassium, sul- branches and leaving a charred sea fur and boron especially promote of standing and fallen dead trees in tree growth, though the size of the their wake (fig. 8). Even where response from different fertilizer these sites burned again, some mixes varies considerably by site. coarse woody debris remained. Repeatedly removing nutrients Dry forests had frequent surface from forests in the form of trees and fires (every 7 to 30 years), and green slash could theoretically tended to have less large wood. reduce tree growth through nutrient Each fire would consume woody deficiencies. How much of a nutri-
5 Table 1. Biomass and selected critical above-ground nutrients in trees (lbs/acre) in stand- ing mixed conifer forest before harvest
Nutrient Total Crown Merchantable Bark Merchantable Wood Biomass 22,205.8 20,062.7 57,462.6 Nitrogen 121.521 54.593 24.448 Potassium 101.183 56.766 79.378 Sulfur 9.365 4.964 6.169 Boron 0.383 0.179 0.263
6 ent reduction has not been studied tion and from nitrogen-fixing plants thoroughly, and would likely vary by and microbes, but this occurs site, intensity and frequency of slowly. A recent study on a western removals, and the time frame being red cedar site in northern Idaho considered.1 But one way of looking found that nitrogen re-accumulated at it is to study the nutrient content at a rate of roughly 4 pounds per of slash. acre per year. A recent case study by the Potassium and other nutrients Intermountain Forest Tree Nutrition also re-accumulate, but even more Cooperative estimated the nutrient slowly, mostly from parent material content of trees in a fully stocked weathering and in miniscule 80-year-old mixed conifer stand in amounts from atmospheric northeastern Oregon, with basalt precipitation. The same study found parent material (table 1). In the potassium re-accumulating at green crowns of this stand, there roughly 2.5 pounds per acre per were an estimated 122 pounds of year. The amounts vary by site, but nitrogen per acre and 101 pounds potassium and other nutrient losses of potassium per acre. A harvest of would be even more important on all the merchantable logs would soils with parent materials that were remove an additional 79 pounds of lower in these nutrients and slower nitrogen per acre and 136 pounds to decompose. of potassium per acre. Allowing rain and snow-melt Most harvests and thinnings do water to leach water-soluble not currently remove or immediately nutrients from fresh slash down burn all this material. A lot of nitro- into the soil retains more of those gen and other nutrients are also nutrients for forest growth and stored in the surface organic layers. health. The amount and rate of The amount of nutrients contained nutrient leaching depends on the there varies with climate and amount tree species and the climate. of disturbance. But since most of Warmer, wetter climates promote our forests respond positively to faster leaching. The amount of those correctly balanced mixes of leached nutrients a site can capture fertilizers, carefully considering and retain depends on the soil possible nutrient implications of texture and organic matter. forest activities and adjusting them Even though fine organic debris where possible could benefit forest contains and recycles the majority growth and health. of a tree’s nutrients, coarse woody Nitrogen naturally re-accumulates debris (CWD) also provides some in forests from atmospheric deposi- nitrogen, since some of the organ-
1 One set of studies (see Powers et al., 2005) found no growth reductions for the first ten years after forest biomass removals, but the researchers cautioned that their findings did not necessarily forecast long-term trends. 7 Figure 10. Decayed logs serve as moisture reservoirs where conifers multiply roots.
Figure 11. The angular texture of some organic debris decay products helps improve soil structure. Figure 13. Ground fires can be lethal to trees with many feeder roots grown into excessively thick duff accumulations.
Figure 12. Most of a tree’s small feeding roots are concentrated in the soil’s upper layers.
8 isms that break it down fix nitrogen contributor of organic matter for from the air. Depending on forest forest soils. As organic material type, bacteria in coarse woody decays and is integrated into the soil 1 debris (CWD) can fix nearly /2 over hundreds of years, it helps soils pound of nitrogen per acre every maintain aeration (spaces between year. This amount, though relatively particles), resist compaction, buffer small, can be important, especially against erosion, and improve water when the site has few nitrogen filtration (fig. 11). fixing plants such as ceanothus or Organic debris, roots, and alder. Organic debris also helps soils mycorrhizal fungi retain nutrients so they will later Where are the roots? be available for forest plants. Regardless of species, most of Organic debris and soil moisture the small roots and root hairs a Organic matter, as any experi- tree uses to take up nutrients and enced gardener can attest, helps water are concentrated near the soil retain soil moisture longer into the surface and surface organic layers growing season by shading soils and of the soil (fig. 12). In surface storing moisture. As organic debris organic layers made deep by fire decays and is incorporated into the exclusion, trees often grow more soil (fig. 10), conifers, grasses, forbs, roots up into this material, to take and shrubs multiply their roots in advantage of the nutrients and these zones to take advantage of moisture there (fig. 13). When these that moisture. These moist soil layers and the roots within them are zones help keep forests resilient in destroyed mechanically or through the face of warmer, drier summers. fire, even the largest tree can be Moist, decaying logs often persist stressed and made more susceptible after wildfires. to death by bark beetles or disease. Organic debris and soil structure Forest soil flora and fauna Soil structure is the physical In addition to roots, forest soils combination or arrangement of soil are alive with a variety of fungi, particles into larger particles or bacteria, worms, insects, and clumps, and the spaces between burrowing mammals such as them. Organic debris improves soil pocket gophers. Different fungi use structure as it is incorporated into different combinations of dead the soil. Leaves, stems and other and living organic matter for their small plant material are important survival. Many forest owners are sources of organic materials in all aware of root diseases, stem decays, soils, but large woody debris can be and other fungi that can kill trees or a particularly significant and unique reduce the value of their wood. But
9 Figure 14. Mycorrhizal fungi form a mutually beneficial relationship with trees.
Figure 15. Ectomycorrhizae cover the outsides of rootlets, just penetrating their outer cells.
Figure 16. The tree seedling on the left was innoculated with mycorrhizal fungi.
10 most forest fungi do not kill trees. can be used by plants); There are hundreds if not thousands • exude or decay into substances of lesser-known microbes and fungi that act as “organic glues,” help- species that help forests function by ing to aggregate soil particles recycling forest nutrients, decompos- and improve soil structure; ing slash, and improving soil physical • move nutrients and even photo- properties. Even native tree-killing synthate (carbon) between trees fungi may be performing a positive -- even between different role by removing trees that are species of trees and shrubs; and poorly adapted to a forest site. • provide food for “fungivores” -- insects, birds, squirrels, deer Mycorrhiza = “fungus root” and many other organisms that One of the groups of fungi that feed on forest fungi. most directly benefit tree growth is called mycorrhizal fungi. Mycorrhizae are essential for “Mycorrhiza” is translated from good growth of many tree species, Latin as “fungus root.” These particularly on nutrient-poor or fungi infect the roots of trees and droughty sites. other plants and form a symbiotic Identifying mycorrhizae relationship (a relationship in Mycorrhizal fungi form relation- which both the plant and the fungi ships with over 95% of the plants on benefit). Mycorrhizal fungi get earth, and there are many different photosynthate (the product of species. Over 2,000 fungi have been photosynthesis - carbon) from trees; reported to form mycorrhizal rela- and the trees get a larger effective tionships with Douglas-fir alone. If root surface to absorb more nutri- you dig up seedlings in the forest, ents and moisture from the hyphae you may notice that the root hairs (the fungus equivalent of roots) and look a little thicker than others you mycelia (matted hyphae) of mycor- have seen. That is because they are rhizal fungi (fig. 14). In addition to covered by mycorrhizal fungi improving rooting surface area and (figs. 15 and 16). absorption, mycorrhizae can also: Mycorrhizal fungi produce • capture and retain nutrients that many different kinds of fruiting might otherwise be leached bodies. Some are above-ground from the soil; mushrooms, such as golden • physically block pathogenic chanterelles (Cantharellus fungi access to tree roots; cibarius) (fig. 17). Other fruiting • exude antibiotic substances that bodies are underground, such as deter root pathogens; truffles. • help “unlock” soil nutrients (convert them into forms that
11 Figure 17. Chanterelles, a popular edible forest mushroom, are the fruiting body of a mycorrhizal fungus.
12 Helping mycorrhizae mineral soil and minimizing Mycorrhizae presence and excessive soil disturbance also development on tree roots depends benefit mycorrhizae. on organic matter. For example, in There is usually no need to add one study of a Douglas-fir forest, mycorrhizae to well-established 77% of the mycorrhizal root tips forests. As with most fungi, were found in the surface organic mycorrhizae spores are abundant layers. Coarse woody debris, as it in native forests. However, trees is integrated into the soil, eventually planted in non-forested areas such benefits mycorrhizae, because as agricultural fields, or dramati- coarse woody debris helps soils cally altered sites such as a retain moisture as it decays. reclaimed mining area, may benefit Minimizing compaction of the from mycorrhizal inoculation.
13 Figure 18. Fine organic debris is smaller Figure 19. Coarse woody debris is larger than 3 inches in diameter. than 3 inches in diameter.
Figure 20. Past harvests left a lot of coarse woody debris.
Figure 21. In some cases, CWD needs can be met by not hauling cull logs to a landing.
14 MANAGEMENT OBJECTIVES FOR Coarse woody debris (CWD) ORGANIC DEBRIS In general, coarse woody debris (logs and other woody pieces 3 Organic materials play a large role inches in diameter and larger) is in forest soils and forest health. The more durable than fine organic quantity and quality of forest debris (fig. 19). Depending on the organic materials is directly and forest type and its inherent distur- indirectly impacted by our forest bances, 25% to 50% of the organic management activities. Fine organic material found in and on a forest debris (materials less than 3 inches soil can be attributed to CWD. in diameter) and coarse woody Coarse woody debris’s contribution debris (materials 3 inches in to forest soils is not immediate diameter and greater) have different but long-term – from decades to functions in a forest, different issues centuries depending on size, decay associated with them relative to fire rate, and the forest’s fire frequency. and bark beetles, and different man- Historical timber harvests tended agement objectives and strategies. to leave more coarse woody debris Fine organic debris (FOD) (fig. 20). Much of the old growth Fine organic debris consists of timber had a lot of decay, and mills small branches, limbs, treetops and didn’t take material below 8 inches similar materials less than 3 inches in diameter. Young forests tend to in diameter (fig. 18). FOD is quickly have much less CWD than older incorporated into the forest floor, forests or those that have its nutrients are readily leached, and experienced insect, disease, fire, it is relatively short-lived – less than or weather damage. 20 years depending on the forest Many second growth stands do type. FOD can be a large fire not have as much malformed wood, hazard if it is not carefully managed due to management activities that because it can quickly combust and thinned poorly formed trees out. carry a fire. Trees are also harvested at younger Leaving FOD distributed across ages, before stem decays develop as the forest floor over winter and fully. Mills now take logs down to longer if possible encourages its smaller top diameters (for example, decomposition and nutrient leach- down to a 4-inch top rather than an ing. The objective in managing fine 8-inch top). All these factors mean organic debris is to recycle the most less coarse woody debris is left on nutrients from it while minimizing site after logging jobs now than in the fire hazard. past timber harvests.
15 Table 2. Coarse woody debris recommendations for maintaining long-term forest growth Climax species1 Target tons per acre for site of coarse woody debris Warmer Drier Ponderosa pine 3 -13 tons/acre Forests Douglas-fir 7-14 tons/acre Grand fir 7-14 tons/acre Western Red Cedar 16-33 tons/acre Cooler Moister Subalpine fir, western Forests hemlock, spruce 16-33 tons/acre Note: These are approximate recommendations. For specific recommendations for individual habitat types, see Graham et al. (1994) in the reference section. 1Climax species are the tree species that would dominate a site after a long period of forest succession (100-400 years) with little or no disturbance. On most forested sites, the climax species will be the most shade-tolerant conifer you can find growing in the understory at a rate of 10 or more trees per acre.
Figure 23. Removing logs with stem decay will not reduce future stem decay on that site.
Figure 22. Wood decay from “white rot” (top) vs. “brown rot” (bottom).
16 Researchers from the USFS them (fig. 21). Measuring how Rocky Mountain Research Station much CWD there is on site before used mycorrhizae as a “bio-indica- a logging job will provide some tor” to determine how much coarse guide to how much additional CWD woody debris was optimal for should be left. See Appendix for Rocky Mountain forest soils. information on measuring coarse They looked at many forest sites woody debris tonnage. and found points of diminishing Leaving larger logs (24 inches in returns for coarse woody debris, diameter and larger) is often where mycorrhizal activity leveled preferable because they decay out above certain amounts of CWD. slowly, are more likely to survive Above the upper limit (table 2), repeated fires, and can provide additional CWD did not increase habitat to a wider variety of wildlife mycorrhizal levels. species than smaller material. For the Inland Northwest, that Ideally, the material should be research recommended leaving distributed across a site. amounts of CWD ranging from Douglas-fir, larch, western red three tons per acre in drier cedar, and pine CWD decay into ponderosa pine forests to 33 tons “red” or “brown” rotted material per acre in more moist western which provides the longest lasting hemlock forests. These CWD benefit (hundreds of years). By con- recommendations assume stumps trast, CWD from grand fir, hemlock, are not removed. and hardwood species is more At a minimum, pay closer short-lived because it is decayed by attention to leaving low value “white rots” (fig. 22). You may (“cull”) pieces of stem wood in the find stem decay in logs left after a forest rather than hauling them all harvest, but removing those logs to a central location, including them will not reduce future stem decay in slash piles, or worse yet, hauling in the stand (fig. 23). them to a mill that won’t pay for
17 Figure 24. Fire risk from CWD, while minimal, may be reduced by cutting the branches from logs so they lay flat on the ground.
18 STRATEGIES FOR MANAGING FIRE The ultimate goal of slash AND ORGANIC DEBRIS treatment is not to remove all slash, but to reduce fire hazard. Therefore, Fire hazard the first step in planning slash Fine organic debris poses the treatments is to determine the greatest fire hazard because it dries degree of slash hazard. The most rapidly, ignites readily, and burns common measure of fire hazard is quickly and intensely, making fires tons of slash per acre, but slash running through it hard to control. hazard is more than weight. Other Fire risk assessment is based prima- factors that determine fire hazard rily on the amount, arrangement, and from slash include: depth of fine organic debris created • number, size and species of by a timber harvest or thinning. trees to be cut and resulting Coarse woody debris is not as slash load in tons per acre much of a fire risk and in some (a few large pieces present a areas, you can legally leave as much smaller hazard than many small of it as you like. However, very heavy pieces even if the tons/acre are coarse woody debris loads (more the same); than 40 tons/acre) may impede fire • depth of the slash (deeper slash suppression. Fire risk from CWD has more fire hazard); may be further reduced by cutting • size of unit (smaller treatment logs’ branches so they lay flat on the units have less fire hazard); ground, where they can soak up • slope and aspect (steep south more moisture and decompose more or southwest facing slopes are easily (fig. 24). more hazardous because they Most western states have fire or dry out sooner and fires on slash rules that require a landowner slopes burn with greater or operator to modify or reduce intensity); slash to an acceptable level. • forest structure (for example, Landowners who have more slash the distance from the ground to than is acceptable may be liable for the base of the tree crowns); any forest fires that start on or move • condition of the unit and through the property. These rules adjoining areas prior to vary from state to state and are often activity; structured differently for slash • location of the unit relative to from logging versus slash from other slash accumulations or pre-commercial thinning or other other fuels; activities. Check with your local • accessibility of the unit -- state forestry office for more whether there are campgrounds information on these rules.
19 Figure 25. Limiting access is one of many ways to reduce fire risk.
Figure 26. Your local state forest fire officials can help you evaluate fire hazard and how to reduce it while retaining nutrients.
Figure 27. Fire hazard can be reduced by lopping slash into smaller pieces – making it less than 24 inches deep.
Figure 28. Heavy winter snows may compress slash considerably.
20 or roads close to the site that Methods to reduce fire hazard allow more opportunities for Lop and scatter human ignition (fig. 25); Relatively small amounts of slash • proximity to structures such can be cut into smaller pieces (2 to as homes; 8 feet in length depending on their • presence of snags and cull trees diameter and limbiness) and (snags ignite easily and can cast scattered so they lay flatter to the sparks and fire brands that help ground, have more contact with the fire spread); forest floor, are less than 24 inches • deterioration rate of slash deep, and are discontinuous so they (slash close to the soil’s surface would be less likely to carry a decomposes more easily and surface fire (fig. 27). loses its needles or leaves more This method, commonly referred quickly, making it less of a fire to as “lop and scatter,” is fairly hazard than loosely compacted standard with pre-commercial fine fuels with lots of brown thinning slash, but it can also be needles); and used for logging slash. Its effective- • time of year activity takes ness in reducing fire hazard is very place. Fine fuels generated in site- and slash-specific, depending the late winter and early spring on tree species, amount, location, create a greater fire hazard than and piece size. slash created in the late sum- For the first few months to years mer, fall, or early winter. Late after the treatment, there is some winter and spring fuels can dry elevated fire risk, depending on the and be highly combustible in the forest type, amount of fuels, and the summer and early fall when intensity of the treatment. It may the fire danger is highest. not be too visually appealing to Before deciding on a slash some landowners either. But after reduction strategy, contact your one winter’s snow, the material is local state forest fire official to often compressed, needles fall off, determine how much of a fire and it is more out of sight (fig. 28). hazard you have, or are likely to Lopped and scattered slash decom- have, from a harvest or thinning poses more quickly on moist sites (fig. 26). If there is or will be enough than on dry sites. slash to warrant further treatment, Pile and burn there are many methods to reduce For heavier slash loads, lop and slash to acceptable levels. The fol- scatter is usually inadequate by lowing methods may be used alone itself. The most common approach or in combination.
21 Figure 30. Dirty piles such as this are difficult to burn.
Figure 29. Piling and burning is the most common approach to reduce slash on family forests.
Figure 31. Leave CWD out of slash pile if possible. Figure 33. Trees can be injured if piles are burned too close to them.
Figure 32. Excavators can separate fine from coarse woody debris more easily. Figure 34. A piece of plastic or roofing paper placed on top of a pile keeps a portion of it dry for easier ignition.
22 to reduce slash hazard on Inland piles do not scorch or damage Northwest forests is to pile it and adjacent homes, buildings, or valued burn it (fig. 29). Piles can be created trees (fig. 33). Covering a portion of by hand or by using a dozer or other slash piles with plastic sheeting, machinery. Hand piling is very roofing paper, or other waterproof appropriate for small areas around material will ensure some dry homes and other buildings; where material for easier ignition (fig. 34). slash loads are light; where Some states have laws regarding the machines would have difficulty types of plastic that can be used for working because of residual tree this purpose and whether it can be density or steepness of slope; or burned. Check with your local state where risk of soil compaction forestry office for applicable and/or displacement is high. regulations. Piles are usually burned Slash can be piled with dozers or during the winter or after fall rains, tractors with rakes (brush blades), to lessen the chance of fires but if they are not used carefully, escaping the piles. these machines can displace large Piling and burning reduces fire amounts of topsoil and forest floor hazard, but it does have some material, and leave a lot of soil in downsides. First, it costs time and slash piles. Piles with a lot of soil in money (especially hand piling), them (fig. 30) are difficult to burn though these costs are usually and can smolder for days and even figured into a logging job that months after they are ignited. They removes sawlogs. Second, there is may even provide an ignition source some risk associated with burning into the next fire season. Dozers piles, both to trees on the site and to also have difficulty separating fine surrounding forests and buildings, organic debris from coarse woody if they are not burned carefully. debris. Tree limbs and boles may Also, depending on the soil type have to be cut into pieces to facili- and its moisture content and pile tate hand or dozer piling. size, the soil under the pile can be Slash can also be piled using severely damaged by heat from the excavators and other machines with fire. These severely burned areas a grapple. Because these machines are often invaded by noxious can select individual pieces of slash weeds such as thistles or spotted to lift, separate, and pile, they can knapweed. However, a very small divide CWD from FOD (fig. 31). percentage of the site is usually Because these machines lift mate- damaged by pile burning, especially rial, piles have less soil, so they burn if old burning sites are re-used. more completely and there is less Finally, immediately piling fresh risk of “hold-over fires” (fig. 32). slash concentrates nutrients in a Pile location is critical so burning few piles. Burning those piles
23 Figure 35. Letting slash sit one winter before treating it retains more nutrients on the site.
Figure 36. Chipping reduces slash risk but can be expensive.
24 typically removes much of those size, cleanliness, and species. Be nutrients and organic matter sure to check with buyers regarding benefits from the site in the form of their specifications before chipping. smoke. Factors such as the quantity and One way to reduce nutrient loss is quality of the chips, transportation to let the slash sit one winter before costs to the site that uses the chips, piling and burning, to allow more and alternative fuel prices also play nutrients to leach to the soil into whether removing the chips is (fig. 35). Most states allow some economically viable. As with burn- leeway or extensions in which to ing, there is also potential for some treat slash before a landowner is nutrient loss, if chipped fresh fine held liable for any fire that moves organic debris, including green from or through the property. In needles, is immediately removed some cases, you may also be able to from the site. get an extension of this time period Even if you do not sell the chips, from your state forestry office. Be you may still prefer to chip your sure to ask them about it before slash and leave it on site. Many logging is completed. There will be people like the way chipping looks. some extra expense, compared to Local air quality ordinances also piling immediately after logging, if sometimes forbid burning, and you have to move equipment back chipping on site may be cheaper to the site to pile slash. than hauling slash to a dump. Wood chips such as those created Chipping by a chipper do not normally occur Chipping involves placing forest in nature. Wood chips dry and wet debris by hand or by a mechanical easily, making it more difficult for arm into a chute leading to spinning fungi and other organisms to knives that reduce material to decompose them. When chips are pieces 2 square inches or smaller. piled or layered, they may retain Chippers are most often pulled moisture and decompose poorly behind a truck or tractor (fig. 36). because of poor air circulation. Chipping has rarely been used for These conditions are very familiar slash treatment because it is labor to ranchers if they bale or stack wet intensive and costly. However, hay and it molds or develops heat there has been renewed interest (spontaneous combustion), or when in chipping, grinding and similar someone finds mold under their wet technologies as a way of creating carpet. Fires moving through a layer biomass fuel, mulch, or feedstock of chips can produce large amounts for petroleum alternatives. of heat, potentially damaging the Chip specifications for these mar- soil and any residual vegetation. kets can be very stringent as to chip
25 Figure 37. Keep chipped slash less than 1 Figure 38. Leave chips in a mosaic, so inch deep. there are areas with no chips. This reduces potential soil impact.
Figure 39. Mechanical slash reduction typically involves some type of attachment to an excava- tor, a bobcat, caterpillar, or simi- lar machine. Figure 40. Fine organic debris can be treated mechanically, but coarse woody debris should be left alone if possible.
26 Layers of chips can also insulate brush so they lay flatter on the the forest floor and mineral soil, ground in contact with the soil. disrupting heating and cooling Most of the machines used for this cycles, water infiltration, and have a rotary or drum power head decomposition. Avoid burying or attached to an excavator, a bobcat, mixing the chips in with the soil, dozer, backhoe, skid-steer tractor, because fungi and other organisms or similar machine (fig. 39). The compete for and tie up nitrogen condition of the material after directly from the soil as they treatment depends on the type of decompose fresh buried chips. head used, skill of the operator, and Because chips can act as a mulch the amount of time spent in an area and be a poor seedbed, they can be or on a piece of slash. used to suppress unwanted All of these machines vary in their vegetation such as noxious weeds maneuverability in tight stands and unwanted shrubs and grasses, (some can be used on sites with or to favor valued vegetation, such trees spaced as close as 12-15 feet), as tree seedlings, deer and elk ability to work on slopes, degree of browse, or bird habitat. However, soil compaction, and the amount of their effect is short lived (from a soil they displace. Small machines few months to a couple of years). and those with the cutting head on Chips can also be used on paths the end of a boom can work close to and trails. Chips are not appropriate buildings and in and among closely within 100 feet of buildings due to spaced trees. fire risk. Most forest owners will hire a If slash is chipped and left on site, contractor to do this work, but some try to keep chips less than 1 inch may be interested in purchasing a deep and distribute them discontin- machine, particularly machines that uously across the site, leaving some can do multiple tasks, such as areas with no chips, to decrease move snow, skid logs, and dig potential impacts (figs. 37 and 38). ditches. For more information, see Avoid chipping coarse woody “Small Area Forestry Equipment” debris. The fire risk from CWD is in the reference section. relatively low, and chips do not These machines can increase the provide the same value to forest amount of slash less than 3 inches soils and wildlife as CWD. in diameter, but fire hazard will be reduced if the material is distributed Busting/crushing/shredding/mulching/ in a patchy pattern across the forest masticating/grinding/chunking floor and in direct contact with soil. Many terms are used to describe Avoid breaking up CWD (fig. 40), different practices that use since this may turn it from low to machines to reduce the size and high fire hazard material. If you stature of slash, small trees, and 27 Figure 41. Minimizing compaction preserves soil pore space and ultimately forest growth.
Figure 42. Using smaller equipment is one way to reduce soil compaction. Figure 43. Limit soil displacement when treating slash.
28 must break up CWD, attempt to leave it in softball- to football-sized • using equipment with lower chunks. Also focus on slash that ground pressure, such as was created in the most recent smaller dozers, and tracks entry. Older slash is not counted in instead of tires (fig. 42); some state slash inspectors’ assess- • working during drier seasons ments, but if breaking up old slash or on snow or frozen ground; makes it countable as new slash, the • limiting traffic by cabling or site may not pass slash treatment carrying slash to the machine; standards. • using machines mounted on an excavator arm; and Soil compaction and displacement • operating equipment over slash One of the most important quali- mats (layers of slash laid down ties of healthy forest soil is adequate specifically to drive on). pore space -- the part of the soil For more information, see occupied by air and water. Pore “Soil Compaction on Woodland space is necessary for tree root Properties,” listed in the reference growth and feeding, and for benefi- section. cial fungi and other soil organisms Soil displacement is also a (fig. 41). Pore space is reduced potential issue with machines, when soil is compacted. Piling and particularly on very thin soils or burning, slash busting, or chipping soils with a unique layer, such as may require moving heavy equip- volcanic ash, that is critical to soil ment across the site. Covering a lot functioning. Soil displacement of ground with repeated trips by occurs most often when machines heavy equipment risks more soil turn and/or twist, pushing the forest compaction. floor and surface mineral layers into Potential soil compaction varies furrows and/or mounds with their by the type of soil and other factors. tires or tracks (fig. 43). Ash-cap soils are very susceptible Blades, rakes, plows, or other to compaction, whereas gravelly or implements attached to tractors sandy soils can be less vulnerable used for logging and/or slash to compaction. Soils with extra treatments can also displace soils. moisture may compact more easily. The more extensive the soil dis- The type of equipment, and the placement, the greater the potential carefulness of the operator using forest productivity loss. Limit soil the equipment, can also affect displacement by minimizing blade compaction. Compaction can be or rake use, and operating logging reduced by: and slash treatment machines care- fully, especially on steep slopes.
29 Figure 44. Broadcast burn Figure 45. Underburn
Figure 46. Burning when the lower Figure 47. Charred CWD will still duff layers are moist helps retain decompose and help soil. nutrients.
30 Prescribed fire tions favorable for smoke dispersal Fires that are ignited purposely to also determine burn timing. treat the forest floor, logging slash, The science and application of and even standing trees are termed prescribed fire have dramatically “prescribed fires.” They are ignited improved. Ideally, prescribed fires under “prescribed” fuel and weather burn in a way that protects the conditions to produce desired nutrient-rich forest floor, leaves outcomes. There are many types of the desired amount of CWD, and prescribed fires. For example, after minimizes the risk of escape. a clearcut, slash is typically broad- “Cool” burns—prescribed burns cast burned (fig. 44) to consume where the temperature is high finer fuels and char coarse woody enough to reduce slash but not hot debris, reduce the fire hazard, kill enough to volatilize all the nutrients unwanted vegetation, create sites —are desirable. When the moisture for seed germination and/or tree content of the surface organic layers planting, and improve tree planter is high, fires do not usually consume access. these layers entirely and tempera- A prescribed underburn takes tures there don’t exceed 400oC place under a canopy of trees and (fig. 46). Above that temperature, burns up needles, limbs, and other nitrogen and other nutrients are materials on the forest floor without volatilized. killing overstory trees. This reduces These forest floor and fine slash fuels or creates bare mineral soil for moisture levels can occur through- conifer seed germination (fig. 45). out the year, but they are most likely These kinds of low intensity during spring and shortly after fall prescribed fires mimic the effects rains. CWD is not usually consumed of surface fires that historically kept under these moist conditions. It may fire risk lower and recycled some be charred, but charred logs have nutrients. plenty of cracks, checks, and other Prescribed burning always openings, allowing decaying organ- balances between choosing isms to colonize the wood (fig. 47). conditions that allow safe burning Prescribed fire can effectively (such as time of the year, fuel reduce wildfire hazard, but it can moisture, air temperature, wind also damage residual trees and speed, humidity, expected rain coarse woody debris. It can also and/or snow) versus conditions damage the forest floor’s nutritional that are dry enough to get a burn and biological values, and even that meets management objectives. mineral soil, if it is not used care- Air quality and atmospheric condi- fully. This is particularly the case in
31 Figure 48. Prescribed burning should be implemented by trained professionals.
32 forests that have been without fire risk that can be used together with for many decades, and deep layers these methods include: of duff have often developed, espe- • making water available; cially around the bases of large, old • limiting access by gating or clos- trees. Before raking these layers ing roads to reduce the chance away from a tree or burning under of human ignitions; it, dig into the duff to see if roots are • creating fuel breaks, fire trails, present. If they are, be careful with or fire lines to limit and isolate fire and other treatments, as trees slash and pre-existing organic could be damaged. debris into smaller subunits and Obviously, prescribed burning break up the fuel continuity; and has large risks. If a fire escapes, a • creating fuel break buffers along landowner can be held legally travel routes (removing all slash responsible for damage to others’ within 66 feet of roads). properties and the cost of suppress- No strategy will eliminate fire ing the escaped fire. Forest owners risk completely, especially when fire who are considering prescribed fire danger is extreme. But healthy trees on their forests should consult with and forests are more resistant and professional foresters and fire resilient to fire, insects, and disease. managers who are trained and Evaluate a combination of different experienced in assessing the risks actions and develop a strategy associated with prescribed fire that best fits your site and your and implementing appropriate objectives, to balance between safeguards (fig. 48). reducing fire risk and meeting other Other methods to help reduce fire risk objectives such as care of forest All of the fire risk reduction soils and wildlife habitat. For on-site strategies referred to thus far are help in devising a strategy to reduce ways of directly reducing or modify- fire hazards from slash, check with ing fuels. Other ways to reduce fire your local state forest fire official.
33 Figure 49. Bark beetles from left to right: Douglas-fir beetle, spruce beetle, pine engraver beetle, and fir engraver beetle.
Figure 50. Pine engravers attack ponderosa & lodgepole pines.
Figure 51. Pine engraver beetles leave piles of orange boring dust in green boles of ponderosa or lodgepole pine on the ground.
Figure 52. “Y”or “H” shaped galleries in the cambium confirm the presence of pine engraver beetles.
34 STRATEGIES FOR MANAGING pines (fig. 50). They usually focus BARK BEETLES AND ORGANIC on sapling to pole sized trees (3- to- DEBRIS 8-inch stem diameter) or tops of larger trees. In the Inland Some landowners believe they Northwest, they can produce 2 should remove all organic debris to or more generations per year. reduce problems with bark beetles. Pine engravers usually attack and Such a preventative mindset is kill trees within a ½ mile of where commendable, but there are many slash with green stemwood has species of bark beetles and only a been created from logging or winter handful of them kill trees (fig. 49). storms. When green pine tops Of the tree killers, only a few larger than 3 inches in diameter are species breed in fresh slash or created and left on site between downed trees. Forest owners November and June, Ips beetles will should consider: attack that material in the spring • species of trees on the site, and breed there. Their progeny and whether a bark beetle that emerge later in the summer to breeds in the coarse woody attack standing green pines. Piles of debris can attack the standing orange-red boring dust on the boles green trees; on the ground (fig. 51) indicate their • the size of the coarse woody presence. Peeling away the bark will debris and whether bark beetles reveal “Y” or “H” shaped galleries can breed in it, successfully from Ips feeding in the cambium complete their development, (fig. 52). emerge, and attack standing To minimize risk from Ips beetles, trees; and avoid creating and leaving fresh • whether the slash is fresh when pine tops or bole wood from the bark beetles are looking for November through June. One option habitat in which to breed. is to log on those sites from July to October. Usually slash created Pine engraver beetle during this time dries out suffi- Pine engraver beetle (Ips pini) ciently to be unsuitable for beetle (also referred to by its genus name development the following spring, “Ips”) is the most common culprit or is colonized by secondary when insects emerge from downed (non-tree-killing) beetles during the trees or larger diameter slash to summer. attack and kill standing green trees If you create green slash larger in the Inland Northwest. Pine than 3 inches in diameter from engraver beetles and their larvae November to June, debark it to feed on lodgepole and ponderosa
35 Figure 53. Debarking green logs will prevent bark beetles from successfully reproducing in them.
Figure 54. Douglas-fir beetle is most commonly a problem from large diameter Douglas-fir trees fallen in winter storms.
Figure 55. Galleries 8-10 inches long, parallel to wood grain, with eggs laid alternately, confirm Douglas-fir beetles.
36 remove beetles’ food (fig. 53), burn they are usually less of a problem in it, or remove it from the site. Green timber harvests, since trees this size stemwood created during winter are usually taken to a mill shortly and spring is often difficult to burn, after they are cut. but to reduce bark beetle hazard, Douglas-fir beetle is most the bark and underlying tissue only commonly a problem from trees need to be scorched to make it that have fallen in winter storms unsuitable for beetle development. (fig. 54). Beetles will attack these Ips prefers slash to standing trees. trees the following spring, and their If you will be logging on a site progeny will emerge a year later to through the summer, and providing attack standing green trees, most fresh tops through July, the beetles often groups of trees. During epi- will move from slash to slash, and demic years, larger groups of trees eventually overwinter in the slash are attacked. The beetles produce or forest floor, without getting to one generation per year. Standing standing trees. This is called leaving green trees do not usually turn a “green chain” for the beetles. The color until one year after attack. following spring they will disperse If you have recently fallen to search out additional fresh Douglas-fir trees larger than 8 downed material and do not usually inches in diameter that have been concentrate attacks in standing on the ground less than 1 year, green trees unless those trees are remove, burn, or debark them. You especially stressed. can also monitor them for beetle You may see evidence of Ips or attack. If you see trees on the other bark beetles in material that ground this size, with red-orange is smaller than 3 inches in diameter. boring dust in bark crevices, and This material usually dries out too upon cutting away the bark find soon for any Ips brood to mature to galleries 8-10 inches long parallel to adulthood, so it is not a bark beetle the wood grain, with larval mines hazard for the standing trees. perpendicular to the main gallery in alternate patches (fig. 55), they have Douglas-fir beetle been attacked and should be As the name implies, the removed, burned, or debarked. Douglas-fir beetle (Dendroctonus pseudotsugae) is a bark beetle that Spruce beetle feeds predominantly on Douglas-fir Spruce beetle (Dendroctonus (it rarely attacks larch). Douglas-fir rufipennis) feeds on all species of beetles attack large diameter stand- spruce. Like Douglas-fir beetle, it is ing trees (larger than 12 inches), and mainly a problem in standing trees green debris larger than 8 inches, so and green debris that is larger than
37 Figure 56. Spruce beetle galleries run parallel to the wood grain but are generally shorter and wider than Douglas-fir beetle galleries.
Figure 57. Fir engraver galleries are 2-4 inches long and perpendicular to wood grain, with smaller larval galleries emanating from them parallel to the grain.
Figure 58. Wood borers such as flat- headed borers (top) and longhorned borers are often found in CWD but rarely move on to kill green trees.
38 12 inches in diameter. Problems mally occur during periods of commonly begin when there is a drought or following outbreaks of large amount of wind-thrown green defoliating insects that stress and spruce. Beetles attack the downed predispose trees to fir engraver trees and their brood emerge from attacks. However, populations may this material 1 or 2 years later to increase enough in downed trees attack standing trees. to kill patches of tree tissue or Fallen spruce trees larger than treetops. Outbreaks can also occur 12 inches in diameter should be among root-diseased trees. removed, burned, or debarked During droughty periods, if you to destroy beetle habitat. have green grand fir larger than 4 Beetle-attacked spruce trees have inches in diameter on the ground, reddish-brown boring dust check under the bark for beetle accumulating in bark crevices and galleries. If you find main galleries on the ground underneath infested scoring the wood perpendicular to logs. Spruce beetle galleries are the grain, and larvae galleries similar to Douglas-fir beetle emanating from them parallel to the galleries, but shorter (fig. 56). grain (fig. 57), remove or debark the stems to eliminate beetle habitat. Fir engraver beetle The primary host for fir engraver Generalizations about bark beetles beetle (Scolytus ventralis) is grand and organic debris fir. While this beetle is not com- A few rules of thumb can be monly as much of a problem with drawn from the biology of the bark downed trees as other beetles beetles that breed in green coarse described here, fir engraver beetle woody debris: sometimes breeds in wind-thrown Trees dead longer than one year grand fir and in the tops of grand fir are not a bark beetle hazard. Even (over 4 inches in diameter) left over if those trees were at one time from logging. Fir engraver beetles infested with bark beetles, their produce one generation per year, brood has already left. You will which attack trees from June to often find insects in them that are September, most often during superficially similar to bark beetles, periods of drought. but they are not usually insects that Not all of the attacks of standing kill trees. The same goes with large trees are lethal. More commonly, fir larvae of wood boring insects com- engraver beetles simply kill patches monly found working in dead trees of tree tissue, or kill tops. Outbreaks or firewood (fig. 58). These insects have never occurred due to popula- rarely kill trees. In fact, they are tion build-up in wind-thrown trees beneficial to forests, because they or logging slash. Outbreaks nor- hasten the process of decomposing
39 Figure 59. Cutting green stemwood into firewood-sized pieces does not eliminate it as bark beetle habitat.
Table 3. Tree species, and recommended slash or downed tree treatments to prevent bark beetle problems
Tree Species Bark beetle Material that must be Material that may treated, and how be left for forest soils and wildlife Ponderosa pine Pine engraver Do not leave green pine Pine slash that is (Pinus ponderosa) (Ips pini) slash larger than 3 inches smaller than 3 inches and Lodgepole in diameter from in diameter, created pine (Pinus November to June. July to October, or contorta) Otherwise burn, chip, or that is more than dozer-trample the slash. 1 year old.
Douglas-fir Douglas- Remove or burn green Douglas-fir stems (Pseudotsuga fir beetle Douglas-fir slash or less than 8 inches in menziesii) (Dendroctonus downed trees larger than diameter or more pseudotsugae) 8 inches in diameter than 1 year old. within 1 year of creation. Those downed from May to July should be taken out before the following April. Engelman spruce Spruce beetle Remove, burn, or debark Spruce stems less (Picea engelman- (Dendroctonus green spruce larger than than 12 inches in nii) rufipennis) 12 inches in diameter diameter or more within 1 year of creation than 1 year old.
Grand fir Fir engraver Remove or burn green Grand fir stems less (Abies grandis) (Scolytus grand-fir slash or blown- than 3 inches in ventralis) down trees larger than diameter or more 3 inches in diameter. than 1 year old.
40 the dead trees. They also provide different species (say, ponderosa food for a variety of wildlife species. pine), you do not have a potential Organic debris less than three bark beetle problem. inches in diameter is never a bark A final note: sometimes landown- beetle hazard. Occasionally Ips will ers see a green tree that has fallen in attack smaller diameter materials, their forest and decide to cut it into but the material usually dries out, firewood-sized pieces and stack it starving the larvae before they up in the woods to cure. Cutting develop fully. green stem wood into firewood- CWD from some species is never sized pieces has little effect on its a bark beetle hazard. For example, suitability as bark beetle habitat. there are bark beetles that breed in Bark beetles that breed in downed woody debris from cedar, hemlock, stem wood will still do this success- and larch, but they do not emerge to fully in firewood-sized pieces (fig. attack standing trees. 59). If downed stem wood is a large Beyond these types of CWD, enough diameter and green enough hazard from bark beetles depends to be a bark beetle hazard, remove on the species, the condition of the it or debark it. material left on the ground, and the For more information on bark size and species of the trees in the beetles and other forest insects, see immediate area that might be the publications cited at the end attacked (table 3). For example, of this booklet. For technical assis- Douglas-fir organic debris may be tance regarding whether you are of appropriate size and freshness in likely to have bark beetle problems the understory, but if the standing as a result of fallen or broken trees, green trees left in the immediate contact your local state forestry area are all too small or of a office or a consulting forester.
41 Figure 60. Pileated woodpeckers and fishers are among the many species that use coarse woody debris.
42 STRATEGIES FOR MANAGING CWD because it provides a WILDLIFE AND ORGANIC DEBRIS cooler, moister habitat with more stable temperatures for Plants, animals, insects, and fungi breeding and other activities; have evolved to take advantage of • birds use CWD for lookout posts forest organic debris for food and and reproductive displays; and habitat. People value these species • small-bodied carnivores such as for their own sake. But even where martens and weasels hunt for the primary focus is on growing small mammals that overwinter wood fiber, some of the organisms under CWD. that benefit from woody debris are important for good tree health. Managing CWD for wildlife can be Rodents transport mushrooms and complicated. The size, distribution spores of mycorrhizal fungi. Birds of and orientation of logs are more prey make their homes in snags, and important than sheer quantity. Also, then hunt pocket gophers that might different wildlife species have differ- otherwise kill planted trees. ent habitat needs, some of which Slash ultimately helps wildlife to may conflict. For example, heavy the extent it enriches forest soils, log concentrations may be good for which in turn feed the plants, trees, small mammals but may limit elk and fungi that wildlife depend on. movement. But for the most part, wildlife biolo- Since many if not most wildlife gists looking at organic debris focus species of interest cross property on coarse woody debris, since it is boundaries, you also have to factor often limited in many forests. In in what needs are being met, or not addition, many species of wildlife being met, on adjacent forests. More rely heavily on CWD for different research is needed, but three gen- phases of their life cycles (fig. 60). eral strategies related to managing For example: CWD for wildlife are often dis- cussed: snags, log sizes and • both birds and mammals use characteristics, and arrangement. CWD as a place to forage for insects or fungi; Snags • martens, fishers, bobcats, and Green trees are sometimes blown black bears use CWD for dens down by the wind and immediately and shelter; provide CWD, but more commonly, • many small mammals use CWD dead trees remain standing for for hiding cover and protection; decades, depending on their • small mammals and amphibians species, size, cause of death, and use logs as protected runways; their local environment. Dead • many amphibians benefit from standing trees are called snags.
43 Figure 61. Trees heavily Figure 62. Leaving snags in affected by insects and disease clumps of trees reduces their are good snag candidates. safety risk.
Figures 63. A single- or double-grip harvester can be used to create a snag and still harvest wood higher in the tree.
Figure 65. Snags and coarse woody debris provide the widest variety of Figure 64. Hollow logs are particularly habitat if useful to many wildlife species. the bark is attached.
44 Snags are valuable for a whole host single- or double-grip harvester, is of wildlife species, and their quality to clip some trees 10-20 feet above and quantity are often the first the ground (fig. 63). This creates things that biologists look for when snag habitat while reducing loggers’ evaluating forest wildlife habitat safety risk. If a tree has stem decay, quality. the worst decay is usually in the A hard snag has intact bark and bottom of the stem. Clipping the top firm wood. A soft snag has some of such a tree may allow the harvest bark remaining, and wood that is of one or more viable logs from the beginning to decay and soften. top part of the tree. Green trees with stem decay also Coarse woody debris size provide habitat for many of the and characteristics same cavity-nesting species that Larger pieces of organic debris use snags. Leave some hard snags, benefit a wider range of wildlife soft snags, and green trees that will species. For example, a black bear be “future snags” (generally the can den in the hollow stump of a bigger the better), distributed over large, wind-thrown tree. The larger the unit. If possible, leave snags the log, the longer it will persist, from a diversity of tree species. providing habitat for a longer Many landowners and loggers period. However, small logs still prefer to leave the least valuable benefit other species. For example, trees as snags, especially if they smaller logs often provide foraging already show signs of animal use, opportunities for many wildlife such as woodpecker activity or species, including bears. cavities. Trees that are already Longer pieces of CWD are also affected by certain insects and preferred because they provide a disease are good candidates for wider range of diameters, in turn snags (fig. 61), especially if they are benefiting a wider range of wildlife of little value for wood and will not species. Hollow logs, created by harm adjacent trees. decay from Indian paint fungus, red Snags can be a safety issue for ring rot, and other stem decays, are loggers and others who work, play, particularly useful to many wildlife or otherwise spend time in the species, such as the pine marten woods, so it is important to be (fig. 64). flexible to allow loggers to leave Snags and downed logs provide snags in locations that do not the widest variety of habitat if the threaten safety. One way of safely bark is attached, since some wildlife leaving snags is to leave them in species will live in the space clumps of trees (fig. 62). Another between the wood and the bark technique, if a site is logged with a (fig. 65). Take care not to roughen
45 Figure 66. Log piles provide a complex of snow-free spaces and runways for wildlife protection and foraging.
Figure 67. Logs lying parallel to slope contours may be used more by wildlife. Such logs will also trap eroding soil on the uphill side.
46 up snags and CWD during logging How much coarse woody debris operations any more than necessary. for wildlife? The amount of CWD to leave Coarse woody debris arrangement depends on your overall forest The arrangement of fallen logs management objectives, but wildlife is an issue for some species, biologists rarely talk about a site particularly small mammals and having too much CWD. Some their predators. For example, researchers have suggested that 5-7 martens and fishers like logs that tons of CWD per acre for ponderosa are “jack-strawed” or loosely piled pine forests and 10-15 tons per acre up across the forest floor. When log of CWD in mixed conifer and piles are covered by snow, they spruce/fir forests will help a wide create a complex of snow-free variety of wildlife species. Other spaces and runways that provide experts recommend leaving three to habitat for rodents and foraging five logs 12 inches in diameter and opportunities for predators (fig. 66). at least 8 feet long per acre. The Log orientation matters too. Logs best strategy may be to leave a lying parallel to slope contours may variety of species in various decay be used more by wildlife than logs stages to benefit a broad range of oriented up- and downhill, espe- species. The publications listed in cially on steep slopes (fig. 67). the reference section of this publica- Arranging logs this way also allows tion provide more details on soil and fine organic matter to managing snags and coarse woody accumulate on the uphill side, debris for different wildlife species. which traps moisture, hastens decay, and reduces fire risk.
47 CONCLUSION On other sites and for other objectives, decisions about Fine and coarse organic debris treating organic debris are less are important parts of a healthy straightforward, particularly as forest. Forest and site conditions related to fire risk and fine organic vary widely across the Inland debris. Landowners should balance Northwest. Forest owner values carefully between their acceptable and goals also vary widely. risk, costs, and potential benefits Therefore, the application of the to plan the best treatment strategy information within this booklet for each site. must be customized for each The information in this publica- unique site and landowner. tion should provide a starting point For some sites, implementing to help forest owners and those the strategies described here may who work with them ask the right require only slight, inexpensive questions to make decisions adjustments to forest practices. towards keeping forests and wildlife For example, coarse woody debris more healthy and sustainable, while objectives on some sites can be met keeping risk from fire and insects by simply leaving larger diameter within acceptable limits. For more slash pieces and cull log pieces information on the topics discussed scattered across the site rather than in this publication, see the refer- hauling them all to a slash pile. ences listed on pages 58-59.
48 A harvester leaving a snag and removing the merchantable part of the tree.
49 APPENDIX: ORGANIC DEBRIS torching, crowning, and resistance ESTIMATES to control) (fig. 68). These photo series may be available through State forest fire officials and state forestry departments. foresters commonly talk about the amount of slash or coarse woody Measuring organic debris debris in terms of “tons” or “tons per If you would prefer to measure acre.” Many forest owners are not coarse woody debris or fine organic sure what a ton of slash or coarse debris directly, you can use the woody debris looks like. Learning planar intersect technique (fig. 69). how to measure organic debris can For coarse woody debris, that in- give you a feel for different debris volves counting sound and rotten amounts. Once you measure it a few pieces of wood (above ground) that times, you may not need to measure intersect 50 or 100 foot transects. as much in the future, especially for • Logs are rotten if they can be CWD, where a fairly wide range of kicked apart. Rotten logs are material is targeted. There are two counted, but for fewer points common ways of measuring organic because they weigh less. debris: photo series estimation and transect sampling. • The transect must intersect the central axis of the log to count Photo series that log — the transect can’t just State forest fire officials and catch the log’s corner (fig. 70). others who inspect woody debris • Splintered logs are mentally and slash loading commonly use molded together to estimate photo series to guide their esti- diameter (fig. 71). mates. These are photographs of a variety of sites with differing • If the same piece crosses the amounts, configurations, and transect more than once it is compositions of slash, which are counted each time (fig. 72). then measured for their fine organic • Look above your head for debris and coarse woody debris suspended CWD (fig. 73). amounts. With this method, you sim- • Snags and stumps are not ply find the photo that most closely counted. matches what you see on your site Different weights per acre are and estimate accordingly. Some then assigned to each piece of wood series also rate the fire potential of according to its diameter and the material shown in each photo soundness or rottenness, and (such as rate of spread, intensity, depending on whether you do 100
50 Figure 68. Photo series are commonly used to estimate slash loads.
51 Figure 69. CWD can be Figures 70. The tape must cross the whole log (left), measured using transects. not just a corner (right) to be counted in a transect. foot or 50 foot transects. Adding targeted tons per acre of coarse those weights together estimates woody debris. the tons of coarse woody debris This method does not count per acre for that transect. Anywhere snags. If your tons per acre seem from 1-3 randomly placed transects low, but you have a lot of snags on per acre are then averaged together the site, you may be fine, since to estimate tons of debris per acre snags will eventually fall and add for the site. Tables 4 and 5 are coarse woody debris to the site. blank, so you can photcopy and use Fine organic debris can also be them for your estimates. Figure 74 measured along these transects, but shows an example of 3 transects. the method is tedious. Pieces are These log diameters are entered on counted in three diameter classes table 6. (less than .25 inch, .25 to 1 inch, & 1 To be precise, these numbers inch to 3 inches) in the first 6 feet of must also include a slope correc- the transect, and added in a similar tion, but as long as the slope isn’t manner to the large pieces, to more than 50%, it won’t increase the estimate tons of slash per acre. estimate by more than 12%. A high The planar transect method for degree of precision isn’t usually slash is used primarily in research. necessary for general management In day-to-day forest practice, photos purposes, because we are typically are most often used to estimate looking at a fairly broad range of slash.
52 Figures 71. Splintered logs are mentally molded together to estimate diameter – this piece would be roughly 5 inches.
Figure 72. If the same piece crosses Figure 73. CWD that is suspended is the transect more than once it is also counted in planar intersects. counted each time.
53 Table 4. Coarse Woody Debris Transect #1 Transect #2 Transect #3 Estimation – 100’ Transects. Diameter Tons per acre # Pieces Tons # Pieces Tons # Pieces Tons and soundness/rottenness per piecea per acre per acre per acre 3” sound .4 3” rotten .3 4” sound .7 4” rotten .6 5” sound 1.2 5” rotten .9 6” sound 1.7 6” rotten 1.3 7” sound 2.3 7” rotten 1.7 8” sound 3 8” rotten 2.2 9” sound 3.8 9” rotten 2.8 10” sound 4.7 10” rotten 3.5 12” sound 6.7 12” rotten 5 14” sound 9.1 14” rotten 6.8 16” sound 11.9 16” rotten 8.9 18” sound 15.1 18” rotten 11.3 20” sound 18.6 20” rotten 14 22” sound 22.5 22” rotten 16.9 24” sound 26.8 24” rotten 20.1 26” sound 31.5 26” rotten 23.6 Total tons Total tons Total tons per acre: per acre: per acre: Average tons per acre:
a Values derived from Brown, 1974. Values are for tons/acre on a 0% slope. 54 Table 5. Coarse Woody Debris Transect #1 Transect #2 Transect #3 Estimation – 50’ Transects. Diameter Tons per acre # Pieces Tons # Pieces Tons # Pieces Tons and soundness/rottenness per piecea per acre per acre per acre 3” sound .8 3” rotten .6 4” sound 1.5 4” rotten 1.1 5” sound 2.3 5” rotten 1.7 6” sound 3.4 6” rotten 2.5 7” sound 4.6 7” rotten 3.4 8” sound 6 8” rotten 4.5 9” sound 7.5 9” rotten 5.7 10” sound 9.3 10” rotten 7 12” sound 13.4 12” rotten 10.1 14” sound 18.3 14” rotten 13.7 16” sound 23.8 16” rotten 17.9 18” sound 30.2 18” rotten 22.6 20” sound 37.2 20” rotten 27.9 22” sound 45.1 22” rotten 33.8 24” sound 53.6 24” rotten 40.2 26” sound 62.9 26” rotten 47.2 Total tons Total tons Total tons per acre: per acre: per acre: Average tons per acre: aValues derived from Brown, 1974. Values are for tons/acre on a 0% slope. 55 Figure 74. Three 100-foot transects.
56 Table 6. Coarse Woody Debris Transect #1 Transect #2 Transect #3 Estimation – 100’ Transects. Diameter Tons per acre # Pieces Tons # Pieces Tons # Pieces Tons and soundness/rottenness per piecea per acre per acre per acre 3” sound .4 1 .4 3” rotten .3 4” sound .7 1 .7 4” rotten .6 5” sound 1.2 5” rotten .9 6” sound 1.7 6” rotten 1.3 7” sound 2.3 1 2.3 7” rotten 1.7 8” sound 3 2 6.0 8” rotten 2.2 1 2.2 9” sound 3.8 9” rotten 2.8 10” sound 4.7 1 4.7 10” rotten 3.5 12” sound 6.7 12” rotten 5 14” sound 9.1 14” rotten 6.8 16” sound 11.9 16” rotten 8.9 18” sound 15.1 18” rotten 11.3 20” sound 18.6 20” rotten 14 22” sound 22.5 22” rotten 16.9 24” sound 26.8 24” rotten 20.1 26” sound 31.5 26” rotten 23.6 Total tons per Total tons per Total tons per acre: 4.7 acre: 8.2 acre: 3.4 Average tons per acre: 5.4 tons/acre aValues derived from Brown, 1974. Values are for tons/acre on a 0% slope. 57 REFERENCES Creighton, J. C. and J. Bottorff. 2000. Habitat management for bats on small For more information on the topics woodlands. Woodland Fish & Wildlife. discussed here, please see the references Washington State University Extension listed below. Most of these are available Misc. 0226. 12 pp. Available online at: online, and some should be available http://www.woodlandfishandwildlife.org/ through your local extension office. pubs/bats.pdf Adams, P.W. 1998. Soil compaction on DeCalesta, D. and M. Deusen. 1988. Is woodland properties. Extension Circular there a place for fish and wildlife in your 1109. Oregon State University Extension woodland? Woodland Fish & Wildlife. Service, 7 pp. Available online at: Washington State University Extension http://extension.oregonstate.edu/catalog/ Misc. 0132. 12 pp. Available online at: pdf/ec/ec1109.pdf http://www.woodlandfishandwildlife.org/ Beckley, B. and K. Windell. 1999. Small pubs/isthereaplace.pdf area forestry equipment. USDA Forest Serv- Ferrell, G.T. 1986. Fir Engraver. USDA Forest ice Technical Report 9924-2820-MTDC, 40 Service Forest Insect & Disease Leaflet 13, pp. Available online at: 8 pp. Available online at: http://www.fs.fed.us/eng/pubs/pdfpubs/pdf http://www.treesearch.fs.fed.us/pubs/11016 99242820/pdf99242820pt01.pdf Graham, R., A. M. Harvey, M. Jurgensen, Bennett, M. and S. Fitzgerald. 2008. Reduc- T. Jain, J. Tonn, and D. S. Page-Dumroese. ing hazardous fuels on woodland property: 1994. Managing coarse woody debris in disposing of woody material. Extension forests of the Rocky Mountains. Research Bulletin 1574-E, 5 pp. Oregon State Univer- Paper INT-RP-477, 12 pp. USDA Forest sity Extension Service. Available online at: Service Intermountain Research Station. http://www.cof.orst.edu/cof/extended/extse Available online at: rv/wildlandfire/DispWoodyMaterialLR.pdf http://www.treesearch.fs.fed.us/pubs/24829 Brown, J.K. 1974. Handbook for inventory- Harvey, A.E., M.F. Jurgenson, M. Larsen, ing downed woody material. General Tech- & R.T. Graham. 1987. Decaying organic nical Report INT-16. USDA Forest Service materials and soil quality in the Inland Intermountain Forest and Range Experi- Northwest: A management opportunity. ment Station, 25 pp. Available online at: USDA Forest Service Intermountain http://www.fs.fed.us/rm/pubs_int/int_ Research Station General Technical Report gtr016.pdf INT-225, 15 pp. Bull, E.L., C.G. Parks, and T.R. Torgersen. Hatz, R. and J. Bottorff. 1991. Managing 1997. Field guide for the identification of ponderosa pine woodlands for fish and snags and logs in the Interior Columbia wildlife. Woodland Fish & Wildlife. River Basin. USDA Forest Service PNW-GTR- Washington State University Extension 390, 55 pp. Available online at: Misc. 0158. 12 pp. Available online at: http://www.treesearch.fs.fed.us/pubs/5303 http://www.woodlandfishandwildlife.org/ Bull, E.L., C.G. Parks, and T.R., Torgersen. pubs/wfw_ponderosa.pdf 1997. Trees and logs important to wildlife in the Interior Columbia River Basin. USDA Forest Service PNW-GTR-391, 40 pp. Available online at: http://www.treesearch.fs.fed.us/pubs/3051
58 Helgerson, O.T. & R.E. Miller. 2008. Keeping Pederson, R. 1991. Managing small wood- your forest soils healthy and productive. lands for cavity nesting birds. Woodland Extension Bulletin 2019. Washington State Fish & Wildlife. Washington State University Extension, 34 pp. Available University Extension Misc. 0160. 5 pp. online at: http://cru.cahe.wsu.edu/ Available online at: CEPublications/eb2019/eb2019.pdf http://www.woodlandfishandwildlife.org/ pubs/cavitynestingbirds.pdf Holsten, E.H., R.W. Their, and J.M. Schmidt, 1999. The spruce beetle. USDA Powers, F.P., D.A. Scott, F.G. Sanchez, R.A. Forest Service Forest Insect & Disease Voldseth, D. Page-Dumroese, J.D. Elioff, Leaflet 127, 12 pp. Available online at: and D. M. Stone. 2005. The North American http://www.treesearch.fs.fed.us/pubs/10967 long-term soil productivity experiment; findings from the first decade of research. Kegley, S.J., R.L. Livingston, and K.E. Forest Ecology and Management. 220, 31- Gibson. 1997. Pine engraver, Ips pini 50. Available online at: (Say), in the Western United States. USDA http://www.treesearch.fs.fed.us/pubs/25278 Forest Service Forest Insect & Disease Leaflet 122, 8 pp. Available online at: Schmitz, R.E and Gibson, K.E. 1996. Dou- http://www.treesearch.fs.fed.us/pubs/11026 glas-fir beetle. USDA Forest Service Forest Insect & Disease Leaflet 5; 8 pp. Available Laudenslayer, W.F., P.J. Shea, B.E. online at: http://www.forestpests.org/ Valentine, C.P. Weatherspoon, and T.E. Lisle acrobat/fidl5.pdf (technical coordinators). 1999. Proceedings of the symposium on the ecology and Town, P. and R.L. Mahoney. 1996. Evaluat- management of dead wood in western ing Wildlife Habitat for Managing Private forests. USDA Forest Service PSW-GTR-181, Forest Ecosystems in the Inland Northwest. 433 pp. Available online at: University of Idaho Experimental Station http://www.treesearch.fs.fed.us/pubs/6718 Bulletin No. 60. 16 pp. Livingston, R. L. 2008. Pine Engraver. Windell, K. and S. Bradshaw. 2000. Under- Idaho Department of Lands, Insect and story Biomass Reduction Methods and Disease No. 1, July 2008. Available online Equipment Catalog. 0051 2826. Missoula, at: http://www.idl.idaho.gov/bureau/Forest MT: U.S. Department of Agriculture, Forest Assist/foresterforum/jul08/ID_No1.pdf Service, Missoula Technology and Develop- ment Center. 156 pp. Available online Morgan, P. & B. Shiplett. 1989. http://www.fs.fed.us/eng/pubs/pdfpubs/pdf Photographic series: appraising slash 00512826/pdf00512826.pdf hazard in Idaho. Idaho Department of Lands, Boise. 117 pp.
59 Photo and Illustration Credits
All photos by the authors except: Mike Amaranthus, Mycorrhizal Applications, Inc.: figure 16 Renee Boyles and Sandy Goodson: figure 68. Originally printed in Photographic Series: Appraising Slash Fire Hazard in Idaho, by Penelope Morgan and Brian Shiplett. Boise, ID: Idaho Department of Lands, 1989, pp. 110-111. Steve Fitzgerald, Oregon State University: figure 27 (right) Idaho Fish & Game (© IDFG – Gary Will 2005 ): figure 60 (bottom) Noah Kroese, illustrator: figures 1, 3, 14, 41, 74 R. Ladd Livingston, Idaho Department of Lands (retired): figures 13, 54 Randy Molina, USDA Forest Service (retired): figure 15 Penny Morgan, University of Idaho: figures 45, 48. David Pilz. USDA Forest Service (retired): figure 17 Potlatch Corporation: figure 20 USDA Forest Service Files: figures 8, 50-52, 55, 57
60 Managing Organic Debris for Forest Health Reconciling fire hazard, bark beetles, wildlife, and forest nutrition needs
Forest organic debris includes tree limbs, boles (trunks), needles, leaves, snags, and other dead organic materials. Common reasons for removing organic debris include reducing fire risk, harvesting forest biomass for energy, reducing bark beetle hazard, preparing a site for tree planting, and aesthetics. All these issues are important. But forest organic debris left on-site is not necessarily wasted. Organic debris protects soil from excessive moisture loss, recycles nutrients for trees and other forest plants, adds structure and organic matter to the soil, reduces soil erosion, and provides food and habitat for a wide variety of wildlife. Forest and site conditions vary widely across the Inland Northwest. Forest owner values and goals also vary widely. Many forest owners are unclear on how to reconcile the potentially conflicting objectives related to forest organic debris. This publication outlines the role of forest organic debris in Inland Northwest forests and provides general management strategies. It will help forest owners and those who work with them ask better questions to plan the best treatment strategy for each site in order to keep forests and wildlife more healthy and sustainable, while keeping risk from fire and insects within acceptable limits.
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