Decayed Wood Advisor

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Summary Narrative:

Advice on Decayed Wood in the Vegetation Condition

 

(EMC_ECB_L)

TABLE OF CONTENTS

SYNTHESIS AND MANAGEMENT IMPLICATIONS


DecAID is a summary of the current knowledge and best available data on dead wood in Pacific Northwest ecosystems. The primary emphasis is on wildlife relationships to dead wood and summaries of dead wood levels from inventory data, however the data are presented in an ecosystem context. Snag dbh, down wood diameter, snag density, and down wood percent cover are statistically summarized using tolerance levels. For details on the statistical summarization of data see the Statistical Basis paper.

There are multiple possible interpretations of the data summaries, and many options for ways to apply the interpretations to forest management. Below we present one option we feel is a reasonable interpretation of the summarized data.

Considerations of scale: landscape and stand levels

Wildlife and inventory data summarized in the DecAID Advisor can be applied to management and planning decisions at a range of spatial scales and geographic extents. The calculated tolerance levels (80%, 50%, 30 %) for wildlife data can be applied to stand-level management. However, we do not advise that a particular tolerance level be applied to all stands across a landscape. Rather, decisions about how to distribute different levels of dead wood across a landscape can be guided by the distribution information from unharvested plots (see paragraph below).

When using the inventory data, analysis areas (landscapes or watersheds) should be sufficiently large to encompass the range of variation in wildlife habitat types and structural conditions that occur in the area in which the inventory data were collected (i.e. representative of variation at the sub-regional scale). It is impossible to specify a single minimum size analysis area that is most appropriate to all ecoregions and geographic areas. However, as a general rule-of-thumb we suggest that analysis areas be at least 20 square miles (12,800 acres, 5,120 ha) in size. This coincides with the small end of the range of sizes typical of 5th-field hydrologic unit codes (HUCs). The exception would be when managing habitats that are rare at a broad geographic scale, even if they are common at the watershed scale (e.g. recent post-fire habitats). Even at the scale of the 5th-field HUC, wildlife and inventory summaries for multiple vegetation conditions will need to be considered in the analysis and planning process.

On the other end of the scale, the wildlife and inventory summaries are appropriately applied to very broad Analysis areas for regional assessments, National Forest planning, and so forth. The maximum size analysis area to which the DecAID summaries should be applied is defined by the geographic distribution of the wildlife studies and inventory plots on which the summaries are based – essentially Oregon and Washington. As at smaller scales, multiple wildlife habitats and vegetation conditions will need to be considered in the analysis and planning process.

If the objective is to manage for general unharvested conditions rather than focusing on wildlife species, mimic the distribution of unharvested acres (unharvested proportion of the landscape) in different snag density classes (Figure EMC_ECB_L.inv-14 and EMC_ECB_L.inv-15) and down wood percent cover classes (Figures EMC_ECB_L.inv-16 and EMC_ECB_L.inv-17) across the landscape. The percentages should be thought of as general guidelines rather than taken literally since the distributions to a substantial degree reflect the plot size and sample design of the inventories (see Caveats and Cautions). For example, in the EMC_ECB_L Vegetation Condition, the data suggest that 22% of the plot-sized areas in the unharvested landscape are devoid of snags > 25.4 cm (10.0 in) dbh, and 32% are devoid of larger (> 50.0 cm (19.7 in) dbh) snags. However, this should not be interpreted that large contiguous areas on the landscape should be devoid of snags. Rather, there are probably numerous areas of varying sizes across the landscape that do not support snags > 25.4 cm (10.0 in) dbh. The majority of the landscape supports densities of snags > 25.4 cm (10.0 in) dbh of up to 45 snags/ha (18/acre) and densities of snags > 50.0 cm (19.7 in) dbh of up to 15 snags/ha (6/acre). Areas of high snag densities do occur on a portion of the landscape. Over a landscape, balancing high density areas of dead wood with moderate and low-density areas may be desirable.

Few data are available on the spatial distribution of dead wood within stands. Wildlife data indicate that at least some species often use clumps of snags and down wood, but it is unclear if this is because such patterns are selected for or just generally available. Further, the wildlife data offer no guidance on the number or size of clumps that should be managed. Agee (1998) suggests patch size in habitats subjected to a moderate-severity fire regime ranges broadly from 2.5 to 250 ha (6.2 to 620 acres).Based on their work in the eastern Cascades of Washington, Lehmkuhl et al. (2006) recommend retention of snags and down wood on the scale of 0.2-0.5 ha (0.5-1.25 acres) patches.

In lieu of actual data, managers should take advantage of naturally occurring clumps in the stands they are managing. Areas between clumps should not necessarily be devoid of snags. To match historic or "natural" conditions, a mix of clumps and more widely distributed snags should occur within and among stands. In the fire-prone areas of this wildlife habitat type, areas of higher amounts of dead wood should be left on parts of the landscape where fire is less likely to frequently consume dead wood and where it is less likely to produce fuels problems. Areas of flat to moderate slope (or the lower 3rd of slopes), concave or straight topography, and north and east aspects are areas that tend to burn less frequently and/or less severely and where snag retention is highest; these are also areas where the highest levels of dead wood were likely to occur historically (Everett et al. 1999, Skinner 2002). At the landscape scale, provide higher amounts of dead wood in moister plant associations and at higher elevations.

Within the Larger Trees Structural Condition Class, canopy closure can range from 10 to 100%. It may not be possible to maintain high levels of dead wood on sites with few trees, especially those sites that are sparse due to inherent site factors such as soil or productivity. Higher density areas of dead wood can be maintained only on sites that currently have high live biomass or have the potential to produce high levels of biomass.

The location of dead wood (particularly snag) clumps may be determined, to a large degree, by operational considerations. See Rose et al. (2001) for a discussion of operational considerations when managing snags.

Considerations for developing, creating and retaining decayed wood elements

It is difficult to predict which snags will be used by cavity nesting species. Odds of a snag becoming used for cavity excavation can be increased, however. Lehmkuhl et al. (2003) studied cavity occurrence in snags in the eastern Cascades of Washington. They found Ponderosa pine to be the most likely species of snag to contain cavities with rates of 28%; Douglas-fir was the next species most likely to contain cavities at 8.4%. Medium and large snag dbh (>= 33 cm (13 in)) greatly increased the odds of a snag containing a cavity, with rates increasing to 45% for Ponderosa pine and 23% for Douglas-fir. Cavities occurred primarily in snags with broken tops. In other parts of eastern Oregon and Washington Douglas-fir is not used to any extent for cavity excavation, while western larch is a more important species (Bull et al. 1997).

The following is a summary of information found in the Considerations for Developing, Creating and Retaining Decayed Wood Elements paper that is specific to the Eastside Mixed Conifer Forest Wildlife Habitat Type.

•  When creating additional down wood by cutting live trees and leaving them on site, be aware of the implications this may have for increases in Douglas-fir beetle or spruce beetle populations and subsequent mortality of additional trees.

•  To manage for a diversity of dead wood associated species and uses: - Provide a variety of tree and snag species. Wildlife species used Ponderosa pine and Douglas-fir that are the prevalent tree species in this habitat type. Wildlife also used the less common western larch. Because of its thick sapwood that readily decays, ponderosa pine snags are often preferred for nest snags (Bull et al. 1997). Quaking aspen, where it occurs is an important species for nesting (Caton 1996).

•  Provide a variety of heights of snags ranging from shorter snags (about 12 m (40 ft)) for some nesting woodpeckers to snags that are taller than the surrounding trees for bats (mean 31 m (102 ft)).

•  Provide a variety of log lengths, though larger logs provide a wider variety of uses. Shorter logs are used by foraging black bear (8.4 m (27.6 ft)) and foraging pileated woodpeckers (11 m (36 ft)). Longer logs of up to 24 m (79 ft) are used by denning marten.

•  Retain a variety of decay stages of snags and down wood because different wildlife species use different decay stages to meet different life history needs. Because of different decay rates among tree species, leaving a mix of species will help retain a mix of decay stages at some future point in time. However, decayed down wood and snags will burn easier in a fire; these logs will need to be protected if they are to be maintained in areas of this wildlife habitat type with a frequent fire return interval; they should be managed for in less fire-prone areas such as north slopes and bottoms of draws in areas with low- to moderate- frequency, moderate- to high-severity fire regimes.

•  Douglas-fir snags tend to remain standing much longer than ponderosa pine snags in this habitat type (Everett et al. 1999).

•  Emphasize large, sound pieces of down wood, which should last through more fire events than smaller, decayed logs. In addition, larger logs provide a wider variety of uses, such as den sites for mammals.

Snag density and dbh

Wildlife data on use of snags in this vegetation condition are available for 26 species and 5 groups of species from 36 studies across the Pacific Northwest. There are some considerations that should be kept in mind with using data from a couple of these studies. Caution should be exercised when using the white-headed woodpecker (WHWO) data, which are from a population where adult mortality is outpacing recruitment (Frenzel 2004). Density of snags may or may not be part of the issue with this species, the WHWO do not rely on snags for foraging and thus may be able to use areas with lower snag densities than other woodpecker species that do forage extensively on snags. The data point for silver-haired bat (SHBA) is much higher than the other data points. These data came from a study in NE Washington (Campbell 1993); snag densities were significantly (p=0.01) higher at roost sites than random sites. However, the plots size was very small (0.071 ha (0.18 acre)), and when snag density in small clumps is extrapolated to a per hectare basis the numbers may be deceivingly high. However, as indicated by the inventory data from unharvested plots, snag densities do occur at these high levels in the East Cascades/Blue Mountains subregion (Figures EMC_ECB_L.inv-2 and EMC_ECB_L.inv-3).

Use of inventory data from unharvested plots to mimic natural conditions may be misleading on drier sites in this wildlife habitat type. Due to decades of fire exclusion, areas with a frequent historical fire regime may have missed several fire cycles. However, additional information on historic amounts of dead wood available in publications from Agee (2002) and Korol et al. (2002) are similar to the inventory data from unharvested plots, as discussed below. These additional sources of information are not specific to any Structural Condition Class.

Korol et al. (2002 and unpublished data) derived historic range of variability (HRV) for snag densities in dry forests with a low-intensity fire regime of 7.2 to 13.5 snags/ha > 51 cm dbh (2.9 to 5.4/acre > 20 in). HRV was determined by subtracting and adding 30% to the average of 10.2 snags/ha > 51 cm dbh (4.1/acre > 20 in). For high-intensity fire regime areas estimates were 9.5 to 17.5 snags/ha > 51 cm dbh (3.8 to 7/acre >20 in) with an average of 13.5 snags/ha (5.4/acre). They derived their estimates through review of the literature and discussion with experts.

Based on work by Wright (1998), Agee (2002) suggested that biomass of snags in moderate-severity fire regime areas dominated by Douglas-fir averaged 40 Mg/ha (17.8 tons/acre) of snags >23 cm (9 in) dbh across the variety of patch types and sizes. Biomass is difficult to convert to snag density without the raw data and wood density used in the calculations, however, this level is 5 times the biomass predicted for low-severity fire regimes in ponderosa pine stands of 8.1 Mg/ha (3.6 tons/acre), which Agee (2002) equated to about 5 snags/ha (2/acre). Following this logic, the 40 Mg/ha value equates to approximately 25 snags/ha (10/acre).

Estimates from Korol et al. (2002) can be compared to the large snag class in DecAID as minimum dbh measured is similar, and estimates from Agee (2002) can be compared to the smaller size class. Estimates from both sources are lower than snag densities from most wildlife data, but are between the 30 and 80% tolerance levels for inventory data from all unharvested plots.

Determining the appropriate density of snags at which to manage will depend on the location of interest in respect to the landscape as a whole. Large areas of the landscape will likely provide low snag densities, but maintenance of high-density clumps across the landscape is supported by the wildlife data and by inventory data from unharvested plots. The inventory distribution histograms should provide insight into the amount of the landscape that should support different snag densities (Figures EMC_ECB_L.inv-14 and EMC_ECB_L.inv-15) (See Considerations of Scale section above).

Down wood percent cover and diameter

Wildlife data on use of down wood in this vegetation condition are available for 7 species and 4 group of species from 7 studies from eastern Oregon, Washington, and western Montana. The data points for black-backed and three-toed woodpeckers (BBWO and TTWO) should be used with caution. These data were collected during a mountain pine beetle outbreak and thus dead wood levels were elevated. In addition, the data include some sites in Lodgepole Pine and Montane Mixed Conifer Forest Habitat Types, which tend to have higher percent cover of down wood than those on Eastside Mixed Conifer sites (Table inv-5b). The data for fungi, however, also indicate an association with high amounts of down wood with an average of 21% cover (Lehmkuhl et al. 2004). Some additional data not included in the cumulative species curves are available. Based on down wood levels in pileated woodpecker home ranges, Bull and Holthausen (1993) recommend managing for 100 logs/ha (40/acre). Harvey et al. (1987) and Graham et al. (1994) recommend managing for up to 36 Mg/ha (16 tons/acre) and 87.5/Mg/ha (39 tons/acre), respectively, for mychorrizal fungi.

Use of inventory data from unharvested plots to mimic "natural" conditions may be misleading on drier sites in this wildlife habitat type. Due to decades of fire exclusion, areas with a frequent historical fire regime may have missed several fire cycles. However, additional information on historic amounts of dead wood available in publications from Agee (2002), Korol et al. (2002), and Brown et al. (2003) are similar to the inventory data from unharvested plots, as discussed below. These additional sources of information are not specific to any Structural Condition Class.

Korol et al. (2002 and unpublished data) derived historic range of variability (HRV) for down wood numbers in dry forests with a low-intensity fire regime of 1.8 to 3.2 logs/ha > 51 cm dbh (0.7 to 1.3/acre > 20 in). HRV was determined by subtracting and adding 30% to the average of 2.5 logs/ha >51 cm dbh (1/acre >20 in). For high-intensity fire regime areas estimates were 12.8 to 23.8 logs/ha > 51 cm in diameter (5.2 to 9.6/acre > 20 in), averaging 18.2 logs/ha (7.4/acre). They derived their estimates through review of the literature and discussion with experts.

Based on work by Wright (1998), Agee (2002) suggested that biomass of down wood in moderate-severity fire regime areas dominated by Douglas-fir averaged 55 Mg/ha (24.5 tons/acre) across the variety of patch types and sizes. Biomass is difficult to convert to down wood cover without the raw data and wood density used in the calculations, however, this level is 11 times the biomass predicted for low-severity fire regimes in ponderosa pine stands of 5 Mg/ha (2.2 tons/acre).

Brown et al. (2003) estimated HRV for downed woody fuel (CWD) using inference from existing inventory data and knowledge of fire history and fuel consumption. They also estimated optimal levels of CWD which balanced risk (excessive soil heating, fire hazards) against benefits (site productivity, wildlife habitat) of different amounts of CWD. For types other than the warm, dry Ponderosa Pine and Douglas-fir forests they report HRV levels of 10 to 27 tons/acre and optimal levels of 10 to 30 tons/acre.

Unfortunately, it is difficult to compare down wood amounts in the literature to each other, or to our inventory estimates, when they are reported in a variety of units (biomass, volume, pieces per area, percent cover). Data in DecAID are presented in terms of percent cover. In addition, studies and our inventory data often used different minimum diameters for down wood, or don’t report the minimum measured diameter. However, conversion factors in Brown et al. (2003) can be used to convert the various sources of information to approximate tons/acre. After converting data in this manner, it appears that estimated down wood levels from unharvested plots in DecAID for Eastside Mixed Conifer wildlife habitat types are lower than levels reported by Agee (2002) which are from the moist end of the EMC habitat type. The high end of the estimates by Korol et al. (2002) overlap the estimates from DecAID. The inventory data are similar to, though slightly lower than, the both the HRV and optimum ranges determined by Brown et al. (2003).

Determining the appropriate amount of down wood for which to manage will depend on the location of interest in respect management objectives and to the landscape as a whole. Large areas of the landscape will likely provide low amounts of down wood, but maintenance of high-density areas and pockets is supported by the down-wood associated species data and inventory data from unharvested plots. The inventory distribution histograms should provide insight into the amount of the landscape that should support different amounts of down wood (Figure EMC_ECB_L.inv-16) (See Considerations of Scale section above).

INTRODUCTION TO VEGETATION CONDITION

Habitat Type Description

The Eastside (Interior) Mixed Conifer Forest Habitat Type is described in Chappell et al. (2001). The following description is summarized primarily from this publication.

Geographic Distribution: The EMC_ECB Habitat Type occurs in the Blue Mountains of Oregon and Washington, south of Wenatchee in the eastern Cascades of Washington, and in the eastern Cascades of Oregon. The Eastside (Interior) Mixed Conifer Forest Habitat Type extends into northern Washington (North Cascades/Rocky Mountains subregion) and into adjacent Idaho, Montana and British Columbia.

Figure EMC_ECB.inv-1 shows locations of forest inventory plots used in the dead wood summaries for Eastside Mixed Conifer Forest Wildlife Habitat Type in the East Cascades/Blue Mountains subregion. “Evidence of Harvest on Plot” indicates if there was evidence of previous harvest activity recorded for the plot, or if there was a road with in the plot area. Data from plots with no recorded harvest or roads were the basis for describing “natural conditions” for this vegetation condition.

Physical Setting for the East Cascades/Blue Mountains subregion:
Climate – mid-montane
Mean annual precipitation – 76-203 cm (30-80 in) as rain and snow
Elevation – usually about 305 to 2,137 m (1,000-7,100 ft), with generally higher elevations to the east.

Composition: Douglas-fir is the most common and most dominant trees species in this habitat, but a wide array of other trees species occur. Lower elevations or drier sites may have ponderosa pine as a co-dominant with Douglas-fir in the overstory and often have other shade-tolerant tree species growing in the understory. On moist sites, grand fir, western redcedar and/or western hemlock are dominant or co-dominant with Douglas-fir. On mesic sites western larch and/or western white pine occur. On colder sites Engelmann spruce, lodgepole pine and subalpine fir occur.

Understory vegetation ranges from open to nearly closed shrub thickets. Common dominant and co-dominant shrubs include: vine maple or Rocky Mountain maple, serviceberry, oceanspray, mallow leaf ninebark, huckleberries, Ceanothus, pinemat manzanita and kinnikinnick. A wide diversity of broadleaf plants occur. Grasses are also common in this forest habitat.

Structural Condition Description

Large tree stands have average tree size (quadratic mean diameter) greater than 50.0 cm (19.7 in) and tree stocking or cover of at least 10%. These stands are usually late-successional, including but not limited to old-growth forests. Very large trees often are scattered throughout the stand. A grass/forb or shrub understory is often present. Stands may or may not have distinct canopy layers.

Vegetation inventory data, based on the entire plot sample, indicate the area within this wildlife habitat type and structural condition class is distributed as follows:

INTRODUCTION TO AVAILABLE DATA

Wildlife data

The wildlife data for the Eastside Mixed Conifer Habitat Type are not divided by subregion. The amount of wildlife data available is low if divided by subregion, and habitat conditions in the subregions are similar. Data from similar habitat types in Idaho, Montana, and British Columbia are also included in the data set. Combining the data allows for a more robust set of cumulative species curves. Where the combined data may be misleading or inappropriate for this subregion it is noted below.

The wildlife data on snags summarized in the cumulative species curves for this Wildlife Habitat Type and Structural Condition Class are for 26 species and 5 groups of species from 36 studies from across the interior Northwest. Data are available for snags used for nesting, denning, roosting, and foraging. Data specific to the East Cascades/Blue Mountains subregion are available for cavity-nesting birds (Bevis1994), woodpeckers (Bull 1980, Nielsen-Pincus 2005, Nielsen-Pincus and Garton 2007), black-backed woodpecker and three-toed woodpecker (Goggans et al. 1988), flammulated owl (Goggans 1986, Bull et al. 1990), pileated woodpecker (Bull 1987), white-headed woodpecker (Dixon 1995, Frenzel 2004, Frenzel unpublished data, Lindstrand and Humes 2009), Vaux's swift (Bull 1991), northern pygmy owl (Bull et al 1987), American marten (Bull and Heater 2000, Bull et al. 2005, Raphael and Jones 1997), black bear (Akenson et al. 1997, Bull et al. 2000), northern flying squirrel (Bevis and King 2005), big brown bat (Betts 1996), long-legged myotis (Frazier 1997, Taylor unpublished data), silver-haired bat (Betts 1998).

An additional study on cavity-nesting wildlife is available from south-central British Columbia (Martin et al. 2004). Most nests (95%) were in aspen. This study is likely applicable only to northeastern Washington, due to differences in habitats compared with most of Oregon and Washington and thus data are not incorporated into the cumulative species curves.

The wildlife data on down wood use summarized in the cumulative species curves for this Wildlife Habitat Type and Structural Condition Class are for 7 species and 4 groups of species from 7 studies from eastern Oregon, Washington, and western Montana. Data specific to the East Cascades/Blue Mountains subregion are available for black-backed woodpecker and three-toed woodpecker (Goggans et al. 1988), pileated woodpecker (Torgersen and Bull 1995), woodpeckers and ants (Torgersen unpublished data), American marten (Bull and Heater 2000), black bear (Bull 1998, Bull et al. 2000), fungi (Lehmkuhl et al. 2004).

Several additional studies report information on wildlife and other species' use of dead wood that was not incorporated into the cumulative species curves. Some of these wildlife studies clearly demonstrated selection by some species for specific amounts and sizes of snags and down wood. Some of these studies presented results only in summary form, such as in regressions and statistical summaries, which we could not use in the species-specific presentations of DecAID. Still, these studies have value in corroborating other evidence of selection patterns.

The following additional information is available for the Eastside Mixed Conifer Forest Habitat Type; links are provided to the annotated bibliography:

To view a list of studies on wildlife species use of snags or down wood click one of the following links. Information on wildlife species, including and in addition to those for which specific snag and down wood use data were available, were taken from the Species-Habitat Relations (wildlife-habitat relationships) database of O’Neil et al. (2001). This additional information includes a full listing of all dead wood associated wildlife species expected to occur in each wildlife-habitat type and structural condition class, and the species’ key ecological functions (see the General Wildlife-Habitat Relations With Wood Decay Elements and Ecological Functions and Processes of Decayed Wood Elements).

Inventory data

Snag data were collected on 277 inventory plots (all sampled area in EMC_ECB_L), including 168 unharvested plots. Down wood data were collected on 273 plots, including 166 unharvested plots (94% of all sampled area in EMC_ECB_L). In this vegetation condition, snags were sampled on all ownerships. Down wood was sampled on all federal lands and on nonfederal lands in eastern Washington. Because the forest area represented by each of these plots varies, the dead wood distributions and size summaries are based on sampled area rather than on numbers of plots, with plots given different weights in the calculations.

Tolerance levels for snag density and down wood cover for the total landscape were based on a subsample of all inventory plots, totaling 105 plots for snags and 102 plots for down wood. Tolerance levels in unharvested forests were calculated using plots on federal lands only (not subsampled): snag and down wood data were available for 159 plots.

Tolerance levels in unharvested forests on federal lands also were calculated using just those plots with measurable dead wood (i.e., based just on plots which included at least one piece of dead wood of the specified minumum size). There were 110 plots with snags > 25.4 cm (10.0 in) , 95 plots with snags > 50.0 cm (19.7 in), 81 plots with down wood >12.5 cm (4.9 in), and 40 plots with down wood > 50.0 cm (19.7 in).

The inventory numbers presented in the Integrated Summary and Synthesis and Management Implications sections are those based on plots with measurable snags or down wood. Summaries based on this subset of plots are compared to wildlife species data, assuming that dead-wood-associated species would occur on those parts of the landscape where dead wood was present. Much of the wildlife use data were collected in plots associated with some type of use of dead wood (e.g., nesting, roosting, or foraging activities).

The minimum size of snag measured was 25.4 cm (10.0 in) dbh and 2.0 m (6.6 ft) tall. The minimum size of down wood measured was 12.5 cm (4.9 in) diameter and 1.0 m (3.3 ft) long.

INTEGRATED SUMMARY OF WILDLIFE DATA AND INVENTORY DATA FROM UNHARVESTED PLOTS

Wildlife and inventory data are statistically summarized using tolerance levels. For details on the statistical summarization see the Statistical Basis paper.

Snag dbh

Down wood diameter

Snag Density

Landscape distribution of snags in “natural conditions”

Data from unharvested plots can assist managers in setting objectives for distribution of snags across the landscape (Figures EMC_ECB_L.inv-14 and EMC_ECB_L.inv-15). In drier portions of this vegetation condition, unharvested plots may not represent "natural conditions" due to decades of fire exclusion. The following data describe distribution of snags on unharvested plots (n=168) in the EMC_ECB_L vegetation condition.

 

 

 

Down wood percent cover

Landscape distribution of down wood in “natural conditions”

Data from unharvested plots can assist managers in setting objectives for distribution of down wood across the landscape (Figure EMC_ECB_L.inv-16). In drier portions of this vegetation condition, unharvested plots may not represent "natural conditions" due to decades of fire exclusion. The following data describe distribution of down wood on unharvested plots (n=166) in the EMC_ECB_L vegetation condition.

 


ANCILLARY INFORMATION ON WILDLIFE SPECIES USE OF DECAYED WOOD ELEMENTS

See Ancillary Data Methods for caveats and information on how these data are weighted, summarized, and displayed.

Tree height

In eastside mixed conifer forests, nest tree height ranged from 7 m (23 ft) for western bluebirds (WEBL) in burned forests to 26.8 m (88 ft) for the pileated woodpecker (PIWO) in green forests (Figure EMC.sp-11). Denning tree heights were only found for the American marten (AMMA) and the black bear (BLBE), with heights of 23 and 24 m (75 and 79 ft), respectively. Resting tree height was recorded for only the American marten, which was similar to denning tree height at 21 m (69 ft). Foraging tree heights were recorded for 4 species, all at either 19 or 20 m (62 or 66 ft), and for a species group of various primary cavity excavators (PCE) at a height of 14 m (46 ft). Roost tree heights spanned the range of tree heights among all uses, with 10.7 m (35.1 ft) being the height for use by roosting three-toed woodpeckers (TTWO), to heights of 31 m (102 ft) used by long-legged myotis (LLMY). Roost trees used by bats typically were among the largest mean heights among all the species and all the uses. Several studies we reviewed noted that bats tended to roost in snags that were taller than the surrounding forest canopy (Weller & Zabel 2001, Vonhoff 1999, Vonhoff and Gwilliam 1999 & 2007, Betts 1998, Ormsbee & McComb 1998, Campbell et al. 1996), however, Vonhoff (1996) found silver-haired bats roosting in trees that were typically below the canopy.

Tree species

Ponderosa pine, Douglas-fir, and western larch were used by the largest diversity of wildlife species, with 28, 25, and 24 different species using each tree species respectively (Figure EMC.sp-12, Table EMC.sp-2).

Ponderosa pine was an important tree species for use by various wildlife species. Franzreb (1985) found it to be one of the preferred forage species for brown creepers in Arizona. Large, live ponderosa pines were used for foraging by white-headed woodpeckers (Dixon 1995) and though rarely available, they were frequently used for nesting by cavity nesting birds in Montana (McClelland et al. 1979). However, most of the records that show ponderosa pine as a species of primary use were parts of studies that were conducted in multiple wildlife habitat types; for example, sites in Bull (1980) were located in both Eastside Mixed Conifer and Ponderosa Pine/Douglas-fir Forest Habitat Types. These sites could not be separated between wildlife habitat types, so all of them were used in both wildlife habitat types in DecAID.

Ponderosa pine seemed to be used for a wide array of purposes, whereas, the primary use of western larch was most often for nesting. Western larch with broken tops and heart rot were the most important nesting snag for cavity nesting birds in Montana (McClelland et al. 1979). Primarily live, western larch were the most important nest trees for Williamson's sapsucker in southern British Columbia (Gyug et al. 2009). Douglas fir was the preferred forage substrate for brown creepers in Arizona (Franzreb 1985), however, it was not used by cavity nesting birds in Montana (McClelland et al. 1979).

Grand fir was used less frequently for nesting purposes but was often used as roosting, resting and bear denning sites. Grand fir was the sole tree species used by nesting and roosting Vaux’s swifts, and all trees used were hollow. Pileated woodpeckers selected grand fir for roosting, but selected against it for nesting (Bull 1987, Bull et al. 1992).

Most of the records that show aspen and other deciduous trees of primary use were part of Caton’s (1996) or Hutto and Gallo’s (2006) work, which were both conducted in western Montana where deciduous trees are a common component of mixed conifer stands. Deciduous trees were strictly used for nesting.

As for the differences in use of tree species by wildlife species (Table EMC.sp-2), nesting hairy woodpeckers and three-toed woodpeckers both used 7 different tree species; more tree species than any other wildlife species used in this wildlife habitat type. Nesting northern flickers used six different tree species. For each of these species, data came from five different studies.

Tree mortality condition

The studies that recorded mortality conditions of trees used by various species showed that the majority of the trees used were dead (Table EMC.sp-3). However, for several species and used, 1/2 or more of the trees were live. This includes: American marten dens, big brown bat roosts, black-backed woodpecker nests and roosts, black bear dens, northern flicker and pileated woodpecker foraging trees, red-naped sapsucker nests in deciduous trees, Vaux’s swift nests and roosts, northern flying squirrel dens, and Williamson’s sapsucker nests in Washington (Table EMC.sp-3). In southern British Columbia, Williamson's sapsucker used primarily live (74%) western larch for nesting (Gyug et al. 2009). Bull et al. (2000) noted that den trees used by black bear were typically broken-topped or had some form of scarring and decay near the den location.

Hollow live trees and snags

Information on hollow trees and snags is summarized in Table EMC.sp-4. Most of the sites used by American marten for denning or resting were in hollow trees or snags (Bull and Heater 2000). Bull et al. (1992) found hollow trees an important roost site for pileated woodpeckers. All roosts were located inside a cavity, with 95% of the 60 roost trees inspected having a roosting cavity created by decay rather than from being excavated by woodpeckers. Hollow trees are also important den sites for black bears (Akenson et al. 1997, Bull 1998, Bull et al. 2000). Hollow trees with top entries were used significantly more by sub-adult female black bears than any other type of den, possibly reflecting a need for more security from larger, predacious adult male bears (Bull et al. 2000). Vaux’s swifts (VASW) also rely heavily on hollow trees for roosting (Bull 1991) and nesting (Bull and Hohmann 1993, Bull and Cooper 1990). In all of these studies, grand fir was the primary tree species used, and except for resting American marten, approximately half or more of the trees used were alive. In all studies, the hollow trees needed to be of a large diameter so that the tree would be large enough at the point of decay or top breakage to accommodate the species that used it. Other authors noted the association of cavity nesting birds with trees containing heart rot, the precursor to the formation of hollow trees (McClelland et al. 1979, Loose and Anderson 1995).

Snag decay

Information on snag decay is summarized in Table EMC.sp-5. There are only two records where foraging use was noted (black-backed woodpecker and pileated woodpecker) and the decay condition for both was hard (Goggans et al. 1988, Bull 1987). All bat roosts noted were located in snags with a moderate decay stage (Vonhof and Barclay 1996, Brigham et al. 1997, Betts 1996 & 1998), while three-toed woodpecker roosts were located in both soft and moderately decayed snags. Only a few species used hard decay class snags for nesting; black-backed woodpecker (Bevis 1994), various nuthatches, chickadees, and squirrels (Steeger and Machmer 1995), and pileated woodpecker (Bull 1987), but they also used other decay classes of snags as well.

Tree top condition

Use of broken top trees was noted to some extent for all bird species found in Table EMC.sp-6. All bird species used the broken top trees for nesting, and the pileated woodpecker also used broken top trees for roosting. Williamson's sapsucker (WISA), pygmy nuthatch (PYNU), and red-breasted nuthatch (RBNU) used primarily broken top snags (Neilsen-Pincus 2005, Hejl et al. 2000). Caton (1996), Goggans et al. (1988) and Kreisel (1998) all noted that nesting black-backed woodpeckers (BBWO) use mainly trees or snags with intact tops. Caton (1996) and Kreisel (1998) also observed the same for nesting hairy woodpeckers (HAWO). For silver-haired bats (SHBA), Betts (1998) noted they used mainly roost trees with intact tops, while Campbell et al. (1996) noted they used mainly broken top roost trees. All other species in Table EMC.sp-6 used a mix of intact and broken top trees.

Down wood length

Down wood length was recorded for only three species in this wildlife habitat type, American marten (denning and resting) pileated woodpecker (foraging) and black bear (denning and foraging) (Table EMC.sp-13, Figure EMC.sp-13). The shortest logs were used by foraging black bear (mean 8 m (26 ft)) and foraging pileated woodpecker (mean 11 m (36 ft)). Denning and resting logs were longer, with marten using logs with a mean length of 24 m (79 ft) for denning and 20 m (66 ft) for resting, while black bear used denning logs averaging 17 m (56 ft). All denning logs were hollow. Bull (1980) found that pileated woodpeckers preferred logs >15 m (49 ft) in length for foraging.

Down wood species

In the Eastside Mixed Conifer Forest Habitat Type, down wood species data were available for 4 species (Figure EMC.sp-14). American marten used primarily grand fir for denning and resting, and secondarily they used western larch. All denning and resting sites for American marten were in hollow logs. Foraging black bear preferred Douglas-fir, western larch and ponderosa pine logs (Bull 1998). Black bear dens that were located in hollow logs were found more often in grand fir (Bull et al. 2000), while dens located under single logs were located more often under Douglas fir, with a similar number under grand fir logs, and a slightly lesser number under western larch logs (Bull et al. 2000). Bull (1998) stressed the importance of the presence of down logs to black bear den sites; specifically she notes that without the presence of down logs, excavated dens likely would not occur.

In northeastern Oregon, Bull (1980) found pileated woodpeckers foraging primarily on Douglas-fir and western larch logs. In Idaho and Montana, Harvey et al. (1987) found mycorrhizal fungi associated with several species of down wood.

Hollow down wood

Hollow logs were used by resting and denning American marten and denning black bear (Table EMC.sp-9). Where log species was recorded, grand fir was the species most often containing hollow log den sites. Bull et al. (2000) sampled a variety of black bear dens in different substrates and found that a higher percentage of the hollow logs dens were in harvested, earlier structural stage forests. Bull et al. (2005) report higher densities of hollow logs (potential rest sites) were significantly higher (P<0.01) in marten home ranges than in unoccupied areas, with an average density of 2.7 hollow logs/ha (1.1/acre) in home ranges.

Down wood decay

A variety of log decay classes were used by a variety of species (Table EMC.sp-10). Bull (1998) found that denning black bear used larger diameter and more decayed logs significantly (p<0.05) more than random. Harvey et al. (1979) found ectomycorrhizae root tips concentrated in decayed wood throughout the growing season on dry sites. In contrast, lichens were found on moderately decayed wood (Bunnell et al. 2008).

GENERAL WILDLIFE-HABITAT RELATIONS WITH WOOD DECAY ELEMENTS

The following tables provide lists of wildlife species that use specific wood elements in this vegetation condition. The lists are derived from the Wildlife-Habitat Relationships database of O’Neil et al. (2001). These are likely to be more complete lists of species than those lists above, for which quantitative field data on snags and down wood were available. The user should review these lists for additions or deletions pertinent to their local conditions and information.This fuller set of wood elements provides for a wide array of wildlife species (Rose et al. 2001).


Additionally, lists of wildlife species with wood decay elements in all forest or woodland wildlife habitats in Washington and Oregon can be found on the DecAID Repository Web Site.

LANDSCAPE-LEVEL DISTRIBUTION OF DECAYED WOOD ELEMENTS: Comparison of Current and "Natural Conditions" Based on Forest Inventory Data

Comparisons of “natural conditions” to the broader landscape condition provide insight into the cumulative effects of forest management and other activities on the amount and distribution of dead wood. The following data compare the 50% tolerance level of dead wood on unharvested plots and all plots (current landscape conditions) in the EMC_ECB_L Vegetation Condition. In this vegetaion condition, especially on drier sites, unharvested conditions may not represent "natural conditions" due to decades of fire exclusion.

Density of snags > 25.4 cm (10.0 in) dbh is the same on unharvested plots and in the entire landscape (13.1 tph (5.3/acre)) (Tables inv.3b and inv.7b). 22% of the unharvested area and 26% of the total area are devoid of snags. 30% of the unharvested area and 22% of the total area support > 30 snags/ha (12/acre) (Figures EMC_ECB_L.inv-14 and EMC_ECB_L.inv-18).

Large snags (> 50.0 cm dbh (19.7 in)) are slightly more dense on unharvested plots (6.0 tph (2.4/acre)) than in the landscape as a whole (5.2 tph (2.1/acre)) (Tables inv.4b and inv.8b). 32% of the unharvested area and 36% of the total landscape are devoid of large snags. 40% of the unharvested area and 34% of the total area support >10 snags/ha (4/acre) (Figure EMC_ECB_L.inv-15 and EMC_ECB_L.inv-19).

Cover of down wood >12.5 cm (4.9 in) diameter is slightly greater on unharvested plots (0.9%) than in the overall landscape (1.3%) (Tables inv.5b and inv.9b). 34% of the unharvested area and 30% of the total landscape do not support any down wood. 42% of the unharvested area and 43% of the total area support >2% cover of down wood (Figures EMC_ECB_L.inv-16 and EMC_ECB_L.inv-20).

Cover of down wood > 50.0 cm (19.7 in) diameter is similarly lacking on both unharvested plots and across the landscape as a whole (0.0%) (Tables inv.6b and inv.10b). Large down wood is absent from 59% of the unharvested area and 55% of the total area. 28% of the unharvested area and 32% of the landscape as a whole contain >1% cover of large down wood (Figures EMC_ECB_L.inv-17 and EMC_ECB_L.inv-21).

RELATIONSHIPS OF FUNGI TO DECAYED WOOD ELEMENTS

Fungi are important to proper ecosystem functioning by providing ectomycorrhizal associations and nutrient cycling as well as being useful as food sources and medicinal sources. Therefore it is desirable to maintain the most fungal diversity possible. Since fungal species vary in resource requirements, the following guidelines for maintaining down wood will assist in providing habitat for a diversity of fungi:
For additional information see the DecAID Fungi Components Document.

CONSIDERATIONS FOR STAND DYNAMICS

General trends of stand dynamics in this habitat type

A discussion of stand dynamics for the Eastside (Interior) Mixed Conifer Forest Habitat Type is found in Chappell et al. (2001). The following discussion is summarized from this publication.

Successional relationships of this type reflect complex interrelationships between site potential, plant species characteristics, and disturbance regime. Generally, early seral forests of shade-intolerant trees (western larch, western white pine, ponderosa pine, Douglas-fir) or tolerant trees (grand fir, western redcedar, western hemlock) develop some 50 years following disturbance; fire is the most common natural disturbance in this Wildlife Habitat Type. This stage is preceded by forb- or shrub- dominated communities. These early stage mosaics are maintained by frequent fires. Early seral forest develops into mid-seral habitat of large trees during the next 50-100 years. Stand replacing fires recycle this stage back to early seral stages over most of the landscape. Many sites dominated by Douglas-fir and ponderosa pine, which were formerly maintained by wildfire, may now be dominated by grand fir. Without high-severity fires, a late-seral condition develops either single-layer or mulitlayer structure during the next 100-200 years. These structures are typical of cool bottomlands that usually only experience low-intensity fires.

List of Insects and Pathogens

For a list of insects and pathogens important in affecting habitat for dead wood-dependent wildlife species in this vegetation condition, see Tables EMC_ECB.fid-1-6. The functional roles of each insect and pathogen are also displayed. Although other insects and pathogens not shown in these tables also occur in this vegetation condition, their influence upon wildlife habitat generally is of minor significance compared to the listed species. The included insects and pathogens were selected because they are known to create or assist formation of dead wood or other structural habitat elements, or to influence the abundance or long-term sustainability of wildlife habitat. Many exert very significant effects, or should be considered when making management decisions.

Pathogens

In this section, inventory data from unharvested plots are compared to data from harvested plots, not to all plots as in other sections in DecAID. This comparison is displayed so that apparent differences in amount of infection by various pathogens as a result of stand manipulation can be seen. The "unharvested" plots include only those where there was no evidence of tree cutting of any kind and there was no evidence of roads. The "harvested" plots included the remainder of the plots. For more details on how "harvest" was determined on a plot see the Harvested v.s. Unharvested document.

Laminated root rot (Phellinus weirii), armillaria root disease (Armillaria ostoyae), and annosus root rot (Heterobasidion annosum) are important causes of small-scale disturbances in Eastside Mixed Conifer, East Cascades/Blue Mountains Forest.

Inventory data on federal lands show 2% and 3% of the plots have trees infected with laminated root rot in unharvested and harvested areas, respectively (Table EMC_ECB.fid-7). This is a disease “of the site” and the causal fungus can survive in large stumps and roots for as long as 50 years (Childs 1963, Hansen 1976, 1979). The species in this habitat most susceptible to this disease are Douglas-fir, grand fir, white fir, and mountain hemlock. Trees of any age or size can become infected when they make root contact with a disease-infected root. These “root disease pockets” expand at a rate of about one foot a year, so the root disease pocket increases in size through time as long as there are host trees available. Additional host trees will began to grow within the root disease pocket but will be short-lived. Immune (e.g., hardwood species) or resistant (e.g., ponderosa pine) tree species will survive and grow within the root disease pockets. As the roots decay, trees will go down, some while still maintaining green foliage. Trees that die from the root disease, or from fir engravers or Douglas-fir beetles which are attracted to stressed, diseased trees, will not remain standing for long (i.e., selecting host trees as wildlife trees within a root disease pocket is not a good idea). These root disease pockets are a source of down wood if in older stands, but would not provide down wood of any appreciable size in younger plantations where host trees were planted within the root disease pocket. For additional information on laminated root rot see report by Thies and Sturrock (1995).

All conifers in this habitat can be damaged by armillaria root disease (Armillaria ostoyae), but there are differences in susceptibility and damage expression dependent upon tree species, site quality, and habitat type (Hadfield et al. 1986). East of the Cascade crest, damage may continue throughout the life of a stand. In plots examined (Hadfield et al.1986) this fungus was always present on cool and moist to warm and moist habitat types, and was always absent in cold and dry, hot and dry, and frost pocket habitat types. Douglas-fir, grand fir, and subalpine fir showed the highest levels of infection when they were the climax species (Hadfield et al. 1986). Inventory data indicate 11% and 17% of the inventory plots in unharvested and harvested plots, respectively, had armillaria present (Table EMC_ECB.fid-7). This may be an overestimate due to the tendency for crews to mark presence of saprophytic forms of armillaria which are commonly seen and which do not behave as a root disease.

Annosus root disease, Heterobasidion annosum,has a high incidence in partially cut stands containing grand, white, or subalpine fir, especially those with multiple harvest entries (Schmitt et al. 2000). This disease can also infect pines, but, generally, would not cause significant mortality in this habitat. Incidence would be highest on ponderosa pine in dry eastside pine types. Inventory data show annosus on 5% and 10% of unharvested and harvested plots, respectively (Table EMC_ECB.fid-7).

There are numerous fungal species which cause decay in conifers and hardwoods in EMC_ECB habitat, and it is common to find heart rot in older trees. The inventory data on federal lands only has specific codes for three of the species, with the remainder being lumped into an “other” category.

Red ring rot (Phellinus pini) can be found in most any species of tree, and is especially common in larger, older trees. Advanced decay caused by this fungus is beneficial to some cavity nesting species, but does not cause trees to become hollow. In this habitat, this decay was recorded only in western larch in harvested habitats (Table EMC_ECB.fid-8).

Annosus butt rot (also caused by H. annosum) is quite common in western and mountain hemlocks. The amount of butt decay is small in trees younger than 120 years, but increases as trees age beyond that, with significant decay in trees over 150 years old. The probability of breakage along the decayed part of the stem increases through time. Decay caused by this fungus, Heterobasidion annosum, will result in a hollow butt and could be very useful to some cavity nesters or animals which make use of hollow logs. Most of Inventory plots coded for annosus in this habitat are for annosus root rot in true firs or pines. Annosus infection and decay is difficult to detect in live hemlocks, and, even in broken trees, it is difficult to find the positive indicator (fruiting body) of this fungus. When decay is detected and the positive indicator cannot be found, the tree would be coded as unidentified root disease or unidentified heart rot.

Indian paint fungus, Echinodontium tinctorium, causes heartrot primarily in true firs and hemlocks. The result is hollow stems which are very useful to cavity nesters and other organisms which make use of hollow logs. On trees >50-cm dbh, very little was recorded in this habitat (Table EMC_ECB.fid-8). This decay is not difficult to find in grand fir in eastern Oregon, so this suggests that there are high numbers of grand firs greater than 50-cm dbh.

There are many species of decay fungi, and there are no specific codes for major ones commonly found on many of the tree species. In this habitat it is rather common for trees >50-cm dbh to have some stem decay (Table EMC_ECB.fid-8). About half the species in the unharvested plots had greater than 10% of the trees coded for unidentified stem decay. Percentages of trees with decay were generally lower in harvested plots.

Dwarf mistletoes can be important in providing nesting or roosting structures for some species of birds and small mammals. Douglas-fir dwarf mistletoe seems to be very abundant in this habitat, with 46% and 28% of the plots with infection in unharvested and harvested plots, respectively (Table EMC_ECB.fid-9). Of the remaining mistletoes most beneficial to wildlife, western larch dwarf mistletoe is the next most common (14% and 9%), followed by mistletoes in ponderosa pine (7% and 14%) and lodgepole pine (6% and 5%).

Insects

Overview: Insect-caused disturbance is very frequent and closely associated with predisposing stand conditions, although natural disturbances such as drought, defoliator outbreaks, pathogens (root diseases, dwarf mistletoes, and white pine blister rust), fire, and wind also play important roles. The high levels of mortality caused by insect and disease activity in Eastside settings are believed to increase fire hazard and the likelihood of stand replacement events. The activity of insects in these forests during historical conditions of natural fire return intervals may have been less evident and was configured differently than it is today. Current conditions in this wildlife habitat type, namely, the high stand densities and high levels of shade tolerant tree species, are unprecedented in extent across the landscape, prompting insects to play a more prominent role in stand dynamics here than in most of the other wildlife habitat types.

The most frequent disturbance caused by insects is small-scale disturbance characterized by dead tops in larger trees, individual dead trees of any size, and small to medium patches of dead medium-size and larger trees. Bark beetles cause most of this small-scale mortality, responding to overcrowded stand conditions and interacting very closely with other natural disturbances.

Mid- to large-scale disturbances occur sporadically and are usually caused by outbreaks of defoliating insects, particularly the Douglas-fir tussock moth and western spruce budworm, and bark beetles such as the Douglas-fir beetle, mountain pine beetle, western pine beetle, spruce beetle and fir engraver. Large-scale disturbances may extend over a period of many years and involve several species of insects and pathogens, e.g., western spruce budworm outbreaks and associated intensification of intensified activity of Douglas-fir beetle, fir engraver, and Armillaria root disease. High levels of mortality across one or more drainages characterize mid- to large-scale disturbances, which are typically manifested as frequently-occurring scattered individual dead trees mixed with small to medium (up to 10 acres) patches of dead trees of all sizes. Stand conditions play an important predisposing role in mid- to large-scale disturbances. Overcrowded stands, the prevalence of shade tolerant species, and the abundance of these conditions on the landscape are important variables determining the occurrence, extent, intensity, and to some degree, duration of disturbance.

Common associations and effects: Pine, Douglas-fir, Englemann spruce, and true fir trees may be killed by their respective bark beetle associates (mountain and western pine beetles, Douglas-fir beetle, spruce beetle, and fir engraver), and defoliators such as western spruce budworm and Douglas-fir tussock moth sometimes kill Douglas-firs and true firs during defoliator outbreaks. Large remnant pine trees and old-growth pine stands growing in overcrowded conditions are highly susceptible to attack by pine beetles. Western larch, western hemlock, cedars, Pacific yew, and hardwoods are not commonly killed by insects, although western hemlock is sometimes affected by defoliators such as black-headed budworm.

Insects causing topkill in mature trees include fir engraver, Douglas-fir engraver, Douglas-fir pole beetle, and pine engraver. These beetles usually behave as secondary agents that are strongly associated with root disease infection, drought stress, tree injury, or other tree stressors.

Important long-term dynamics: Defoliator effects are complex, varying with initial stand conditions, presence or absence of root disease, and duration and intensity of defoliation. For example, heavy western spruce budworm defoliation may cause multi-storied mixed conifer stands having a large/giant-size overstory component of non-host species and Douglas-fir and an understory of true fir to shift toward a single-storied, more fire-resistant condition for several decades (Hummel 2001). Under similar stand conditions in other instances, budworm defoliation causing nearly total mortality of the understory canopy layer may result in an increased risk of a stand replacement fire event (Hostetler, pers. comm.). Moderately-defoliated mature stands with a large/giant-size overstory component of Douglas-fir and an understory of true fir sometimes experience extensive mortality of the overstory component caused by Douglas-fir beetle in the latter years of a budworm outbreak (Hostetler, pers. comm.). Mature stands with a high component of mature true fir seem to experience a mosaic of mortality conditions ranging from light topkill and understory effects with minimal overstory mortality, to patches up to 10 acres in size of nearly 100 percent mortality. See EMC_ECB_S for additional discussion.

Bark beetle effects are similarly variable, depending upon initial stand conditions, attack intensity, and duration. In general, pine beetle activity tends to accelerate the natural succession of mixed conifer stands to predominantly shade tolerant species, because pine beetles remove the shade-intolerant pine component. In nearly pure pine stands pine beetles may merely thin, or may remove significant portions of the large/giant tree component. In a fashion similar to pine beetles, Douglas-fir beetle and spruce beetle tend to remove the larger trees present in a stand during outbreaks, at times returning stands to an earlier developmental phase (when most of the mature trees are killed) or accelerating their succession to a more shade-tolerant species composition. Riparian areas dominated by mature Englemann spruce often experience significant losses of vegetative cover during spruce beetle outbreaks.

Please refer to insect descriptions for species-specific information on outbreak dynamics, stand effects, and predisposing conditions.

Fire

Fire is the predominant natural disturbance in this wildlife habitat type. Historically, this wildlife habitat type was characterized by a mixed-severity fire regime (Agee 2002). Mean fire return intervals for low- to moderate-severity fires varied from 30 years to about 100 years in presettlement times (Agee 1993). Inland Pacific Northwest Douglas-fir and western larch forests have a mean fire interval of 52 years; typically, high-intensity, stand-replacement fire-return intervals are 150-500 years (Chappell et al. 2001). Specific fire influences vary with site characteristics; wetter sites tend to burn less frequently and stands are older with more western hemlock and western redcedar than drier sites (Chappell et al. 2001). Tree-based modeling by Mckenzie et al. (2000) predicts increasing fire return intervals to the north and at higher elevation.

Since the early- to mid-1900’s, fire exclusion has reduced the frequency of fires and many drier forests on the east side of the Cascades have missed at least one fire cycle. Current levels and composition of wood decay elements likely do not accurately reflect “presettlement” or “natural” conditions in these forests, even in unharvested stands.

Natural accumulation of dead wood in fire-dominated ecosystems is a balance between creation and decomposition and/or consumption of dead wood by fire. The amount of dead wood created is influenced by tree growth (influenced by site productivity), or how much biomass is produced on a site, and the lethal effect of the fire, or how much of the live biomass is killed by a fire, or other mortality factors.

Consumption of dead wood by fire is highly variable among forest types, from fire to fire, and within a given fire, and is effected by size and moisture content of dead wood as well as the amount of fuels and the distance between adjacent fuels (Harmon 2002). Larger dead wood is slower to dry out and decay and thus less likely to be consumed by fire (Harmon 2002, Skinner 2002). As dead wood decays and breaks into smaller pieces, however, it is more readily consumed by fire, thus most large wood in this wildlife habitat type probably did not survive fire long enough to reach advanced stages of decay (Skinner 2002). Accumulation of finer fuels is not necessary for consumption of large dead wood if decay is present and can be ignited by sparks (Evers, personal communication).

Historically, low- and moderate-severity fires killed thin-bark species and smaller trees, but thicker-barked Douglas-fir, ponderosa pine, and western larch survived; some dead wood biomass was consumed (Agee 1993). While low- and moderate-severity fires were the most common, stand-replacing fire events were interspersed at longer intervals, which created pulses of dead wood (Agee 1993).

There are conflicting theories and opinions, but little empirical data, on the influence of fire exclusion on wood decay elements, primarily on the balance between creation and consumption of dead wood by fire (Agee 1993, Agee 2002, Everett et al. 1995, Harmon 2002, Skinner 2002). Thus there is disagreement on whether current dead wood levels in unharvested forests are higher or lower than in pre-fire-exclusion forests, and to what degree. The answer likely depends primarily on habitat type and location of the stand. Unfortunately, monitoring of current prescribed fires and wildfires offer little insight on historical creation or consumption of dead wood due to increased fuels resulting from decades of fire exclusion (Everett et al.1995). Therefore, “we will continue to be limited to conjecture in regards to the historical or reference spatial/temporal dynamics of down woody material in regions characterized by annual summer drought and frequent fires” (Skinner 2002).

Assumptions underlying the estimates of historical dead wood abundance varies. Agee (2002) assumes low severity fires consumed log biomass and killed few trees resulting in relatively low estimates of dead wood abundance. Harmon (2002) disbutes the assumption that fires consumed large amounts of dead wood. In moderate severity fire regimes, Skinner (2002) and Agee (2002) both assume that dead wood levels were a combination of inputs from trees killed by the fire and dead wood consumed by the fire.

Analysis done for the Interior Columbia Basin Ecosystem Management Project compared current and historical dead wood abundance at the landscape scale. Their information was based on review of the literature and consultation with experts. In some habitat types in the Columbia River Basin, fire suppression has allowed the development of dense stands of shade-tolerant and fire-intolerant trees. These stands are stressed, resulting in high mortality of small trees and thus increased levels of small dead wood; overall, however, densities of smaller snags (<53 cm) have declined slightly from historical level in the Columbia River Basin as a whole (Korol et al. 2002). Large snags (>53 cm) have declined from historical conditions due to timber harvest and firewood cutting (Korol et al. 2002). Amounts of both large and small down wood are above historical levels due to the long-lived nature of down wood and fire suppression (Korol et al. 2002).

ECOLOGICAL FUNCTIONS AND PROCESSES OF DECAYED WOOD ELEMENTS

In this section information is presented on the array of ecological functions of wildlife species that in turn are supported by wood decay elements in this vegetation condition. That is, wildlife species play specific ecological roles called “key ecological functions” (KEFs) in their ecosystems (also see the Glossary). The extent to which wildlife species are associated with wood decay elements, and the degree to which such elements are provided, helps support an array of KEFs performed by those species. In general, a community that is more functionally diverse and functionally redundant (more species playing each ecological role or that pertain to each KEF category), will likely be more resilient and resistant to disturbance perturbations than will a community that is less functionally diverse or redundant (Marcot and Vander Heyden 2001). Information presented here on KEFs of wildlife is taken from the WHR database of O’Neil et al. (2001).

List of Key Ecological Functions (KEFs) of Wildlife Species Associated With Wood Decay Elements

The following tables list species’ ecological functions that are afforded by wood decay elements. The manager can use this information to determine which ecological functions might be present in a broad area if such wood decay elements were to be provided. Functional redundancy (number of wildlife species) by KEF category of species found in this vegetation condition can be viewed in Table EMC_L.kef-1.

Lists of KEF categories for wildlife species found in the vegetation condition that use the following specific wood elements can be viewed by clicking the links below:
Additionally, lists of wildlife species with key ecological functions affecting wood decay elements in all forest or woodland wildlife habitats in Washington and Oregon can be found on the DecAID Repository Web Site.

Ecosystem Processes Related to Wood Decay

Wood decay elements provide resources and substrates for many organisms and biological processes that perform vital ecological roles that contribute to overall ecosystem health, soil productivity, and growth of desired plant species. Such processes are part of natural, healthy ecosystems but few studies have quantified them.

Down wood serves as moisture reservoirs, sources of beneficial mychorrizal fungi, nurse logs for many tree and shrub species, and sources of soil organic matter, and also provides other beneficial ecosystem processes. Disturbance events such as fire and blowdown begin a process of releasing useful nutrients stored in woody structures as wood decay proceeds. Decaying tree roots also can contribute to soil nitrogen and soil water-holding capacity, and reduce soil compaction.

Many forest-dwelling mammals disperse spores of beneficial mychorrizal.

Removing woody structures can have short-term benefits to planted seedling growth but longer-term adverse effects on overall forest productivity.

Wildfire can greatly increase the net amount of down wood in a stand, whereas clear-cutting tends to decrease it. Human safety can be a major concern with wildfire or prescribed fires and may override the need to retain wood decay elements in fire-prone forests near human habitations.

For more details see the Ecosystem Processes Related to Wood Decay Document.