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Appendix F – DecAID Analysis

DecAID Project Analysis: Downed Logs and Snags

A collection of information, referred to as DecAID, has been developed by Region 6 to help projects 

identify the levels of snags and downed logs required to meet wildlife population needs (Forest Service 

2012). At the landscape level, DecAID recommends providing dead wood at levels within the range of 

historic variability. The proposed treatments are entirely within the 5th field Breitenbush River watershed 

which was used to evaluate deadwood at the landscape level for this project. 

DecAID evaluates deadwood levels by wildlife habitat type. The Breitenbush River watershed contains 

about 29,655 acres of Montane Mixed Conifer Forest and 31,949 acres of Westside Lowland ConiferHardwood Forest habitat (Acker 2015). Treatment units in the HWY 46 timber project are in these 

habitat types.

DecAID takes advantage of the spatially-comprehensive dataset of vegetation structure developed for 

Oregon and Washington by a team from the Pacific Northwest Research Station and Oregon State 

University using the statistical imputation method Gradient Nearest Neighbor (GNN) (LEMMA 2015). 

DecAID includes a process (“Distribution Analysis”) that allows use of GNN data to evaluate the current 

frequency distribution of different densities of snags and amounts of cover of down wood within 

geographic areas such as watersheds selected by users. By using inventory plot data from unharvested 

areas and information on historic disturbance regimes, the process also allows estimation of reference 

conditions for both snags and down wood (Forest Service 2012).

The median historic condition for the Breitenbush River watershed was estimated using levels of snags

and downed logs found in strategic plots in unlogged stands of various ages and an estimate of the 

normal distribution of seral stages derived from the assumed fire return interval (Acker 2015). Median 

values are the mid-point where half of the time deadwood levels would be at or higher than that value 

and about half the time they would be at or lower than the value. Studies have indicated that fire 

frequency and severity varied considerably in the past due to substantial variability in weather 

conditions, and fire severity varied from century to century (Wimberley et al. 2000). Therefore, levels of 

dead wood have fluctuated considerably over time and plus or minus 50% of the estimated median 

value was used to approximate the historic range of variability. 

Downed Logs: DecAID analysis (Acker 2015) found that downed logs in both total size class (> 5” 

diameter) and large size class (>20” diameter) for both Westside Lowland Conifer-Hardwood Forest and 

Montane Mixed Conifer Forest in the Breitenbush River watershed were similar to estimated historic 

median conditions. (Figures 1-4). That means that the abundance of downed logs currently is similar to 

what was historically present within the Breitenbush River watershed.
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Figure 61.DecAID analysis showing estimated current and historic downed wood for the Breitenbush River 

watershed in Westside Lowland Conifer-Hardwood Forest habitat (Acker 2015).

Figure 62 DecAID analysis showing estimated current and historic large-diameter downed wood for the 

Breitenbush River watershed in Westside Lowland Conifer-Hardwood Forest habitat (Acker 2015).
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Figure 63. DecAID analysis showing estimated current and historic downed wood for the Breitenbush River 

watershed in Montane Mixed Conifer habitat (Acker 2015).

Figure . DecAID analysis showing estimated current and historic large-diameter downed wood for the 

Breitenbush River watershed in Montane Mixed Conifer habitat (Acker 2015).
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Snags: DecAID analysis (Acker 2015) found that snags in both total size class (> 10 inches dbh) and large 

size class (>20 inches dbh) for both Westside Lowland Conifer-Hardwood Forest and Montane Mixed 

Conifer Forest were less than estimated historic median conditions. (Figures 5-8). In particular, the 

percent of area with no snags is much higher now than what historically occurred, according to the 

DecAID analysis. For snags greater than 10 inches dbh, 26% of the Westside Lowland Conifer-Hardwood 

Forest and 22% of the Montane Mixed Conifer Forest in the Breitenbush River watershed have no snags 

compared to an estimated historic median condition of 5% and 6%, respectively (Acker 2015). For snags 

greater than 20 inches dbh, 38% of the Westside Lowland Conifer-Hardwood Forest and 40% of the 

Montane Mixed Conifer Forest in the Breitenbush River watershed have no large snags compared to an 

estimated historic median condition of 11% and 15%, respectively. Past logging and fire suppression are 

likely important reasons why large areas in the watershed lack snags.

Figure 64. DecAID analysis showing estimated current and historic snags for the Breitenbush River 

watershed in Westside Lowland Conifer-Hardwood Forest habitat (Acker 2015).
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Figure 65. DecAID analysis showing estimated current and historic large snags for the Breitenbush River 

watershed in Westside Lowland Conifer-Hardwood Forest habitat (Acker 2015).

Figure 66. DecAID analysis showing estimated current and historic snags for the Breitenbush River 

watershed in Montane Mixed Conifer habitat (Acker 2015).
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Figure 67. DecAID analysis showing estimated current and historic snags for the Breitenbush River 

watershed in Montane Mixed Conifer habitat (Acker 2015).

Cavity Excavator Snag Population Potential Analysis:

The Willamette National Forest Plan has a Standard and Guideline (FW-121) that states: “Habitat 

capability for primary cavity excavators shall be maintained to provide for at least 40% or greater 

potential populations. Habitat shall be provided and monitored at the subdrainage level.” The method 

that the Forest Plan used to calculate habitat population potential is no longer considered “best science” 

for determining that viable populations will be maintained but it does provide for a minimum number of 

snags at the watershed scale.

In order to determine the current distribution of large snags and the capability of the landscape to 

support primary cavity excavators, an analysis was conducted at the forest level for all 5th field 

watersheds using the DecAID snag estimates (Willamette SO, wildlife files). 

The 20 inches dbh and above size class available in the DecAID snag analysis data was used in these 

calculations, while the snag population potential method is based on 18 inches dbh and above. 

Consequently, the results slightly underestimate population potential because snags 18-19.9 inches dbh

are not counted. Snag habitat potential in each watershed did not include acres on private land since the 

population potential standard applies to Forest Service lands.

The calculations indicate that, on the Willamette National Forest, there is a current snag population 

potential of about 54% in the Westside Lowland Conifer Hardwood habitat type and 56% in the Montane 

Mixed Conifer habitat type. In the Breitenbush River watershed, the current snag population potential is 

estimated at about 50% in the Westside Lowland Conifer Hardwood habitat type and 46% in the 

Montane Mixed Conifer habitat type. The analysis suggests that the Hwy 46 project area is above the 

minimum snag population potential, but that snag abundance is lower than the average condition across 

the Forest.
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Table 1. Estimated Snag Population Potential for the Westside Lowland Conifer Hardwood (WLCH) and 

Montane Mixed Conifer (MMC) Wildlife Habitat Types in the Breitenbush River Watershed and in Willamette 

National Forest.

Analysis Area Habitat Type Current Historic 

Breitenbush River Watershed WLCH 50% 77%

Willamette National Forest WLCH 54% 75%

Breitenbush River Watershed MMC 46% 74%

Willamette National Forest MMC 56% 74%

Total acres of land in the planning area are 31,081 acres which for this analysis is reduced by estimating 

acres in areas that are not capable of functioning as habitat in the future such as cliffs, talus, roads, 

lakes, rivers and private land. The estimated acres deducted included 160 acres of private land owned at 

Breitenbush Hot Springs, 311 acres of powerline corridor, 70 acres of cliffs and talus, 30 acres of river 

and 60 acres of roads. Total acres deducted from non-habitat acres is 631. Total acres capable of 

growing owl habitat is 31,081 – 631 = 30,450 acres. 

Of the Hwy 46 planning area 24,552 acres are within a Critical Habitat Unit (CHU) for Northern Spotted 

Owl Recovery. This represents 78.99% of the planning area in CHU. The objective of this land use 

allocations is to provide primary constituent elements (the physical and biological features of critical 

habitat essential to a species’ conservation) identified in the spotted owl critical habitat final rule include 

those features that support nesting, roosting, foraging, and dispersal (USFWS 1992b).

Of the Hwy 46 planning area 14,530 acres are within Late Successional Reserve RO214. This represents 

47.72% of the planning area in LSR. The objective of this land use allocation is to protect and enhance 

conditions of late-successional forest species. Late-successional reserves are designed to maintain a 

functional, interacting ecosystem.

As overlap occurs with CHU and LSR when these allocations are combined with overlap considered they 

total 27,452 acres or 88.32% of the Hwy 46 planning area.

The 11.68% of the analysis area outside the LSR and CHU designations contains riparian reserves which 

add to mature forest habitat.

Growth models and existing condition models are designed to assist the decision maker with 

determining what options to choose. As higher level direction has already determined that over 88.32% 

of the analysis area is focused on developing older forest habitat a detailed growth model analysis is not 

needed.

DecAID analysis suggests the current snag and down wood levels are below historic levels and above 

minimum levels for population viability. In addition to the model information two factors should be 

mentioned. 1) A large fire occurred north of the Breitenbush River and was concentrated in the Western 

part of the analysis area. There were areas to the east of this concentration that were also burned 

extending to the forest boundary. The year of origin of the trees growing in the burned area is 1893 

which in 2017 makes these trees 124 years old. The burned area is approximately 5,000 acres. Model 

results will show the burned area to be low in snag and down wood levels when in reality these trees 

have grown larger and have become mature forests. 2) The Eagle Rock fire south of the Breitenbush 

River at the western edge of the planning area occurred in 1967. The Eagle Rock stands are close to 
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having large enough trees for commercial thinning. During the planning process it was decided that this 

area would be deferred into the future. The model would show this area to be low in snags and down 

wood when in reality it is contributing to smaller diameter material and would soon begin producing 

larger snags and down wood.

Snags and down wood are prescribed where regeneration harvest is proposed to occur in early seral 

habitat creation and gaps over one acre. The number of snags and down wood are listed in the Forest 

Plan Section of the Snags and Down Wood analysis. A detailed unit by unit prescription will be available 

in the project file.
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Effects of fires of 2017 on snag densities

Effects of fires of 2017 on snag densities in the Breitenbush River watershed Willamette National Forest

S. Acker, Northwest Oregon Ecology Group

January 16, 2018

Introduction and Methods

To provide support for project planning on the Willamette National Forest, we used information from 

the analytical tool DecAID (Mellen-McLean et al. 2012) to estimate densities of snags in the Breitenbush 

River watershed after the fires of 2017, for comparison to quantities estimated prior to the fires. 

Interpretation of deadwood information from DecAID is most appropriately done at spatial scales large 

enough to include variability in stand structure and wildlife habitat, typically 5th-field watersheds or 

other areas of at least 20 square miles or 12,800 acres (Mellen-McLean et al. 2012). Analysis of snag 

densities within the watershed is appropriate for two wildlife habitat types identified in DecAID: 

Montane Mixed Conifer Forest and Westside Lowland Conifer-Hardwood Forest habitat types, which 

occupy 29,655 and 31,949 acres, respectively, in the watershed.

DecAID takes advantage of the spatially-comprehensive dataset of vegetation structure developed for 

Oregon and Washington by a team from the Pacific Northwest Research Station and Oregon State 

University using the statistical imputation method Gradient Nearest Neighbor (GNN) (LEMMA 2015). 

DecAID includes a process (“Distribution Analysis”) that allows use of GNN data to evaluate the current 

frequency distribution of different densities of snags within geographic areas such as watersheds 

selected by users. By using inventory plot data from unharvested areas and information on historic 

disturbance regimes, the process also allows estimation of reference conditions (Mellen-McLean et al. 

2012).

GNN uses spectral data from satellite remote sensing as well as physical environmental data to relate 

inventory plots to the vast majority of forested portions of Oregon and Washington lacking field 

measurements (LEMMA 2015). The use of remote sensing data, which are collected frequently, permits 

periodic updating of the GNN dataset to capture current conditions. The most current GNN dataset 

incorporates remote sensing data from 2012, and is incorporated into the most current version of data 

for Distribution Analysis. Major disturbances since 2012 would not be captured in the latest dataset. 

However, the DecAID team has developed an algorithm to exploit RAVG (Rapid Assessment of 

Vegetation Condition after Wildfire) data for wildfires of at least 1000 acres (U.S. Forest Service 2015) in 

ArcMap to estimate effects on density of snags (C. Belongie and K. Mellen-McLean, pers. comm.). In 

2017, this method was updated by Jeremy Hobson, Geospatial System Specialist, and Ray Davis, 

Monitoring Lead - Older Forests & Spotted Owls, (both U.S. Forest Service) to take advantage of higherresolution data from the Sentinel 2 satellites of the European Space Agency which have recently become 

available (Hobson 2017). Maps of fire severity are now available from 2012 to 2017, with Sentinel as the 

source for 2017, and RAVG for the earlier years (J. Hobson, pers. comm.).

The algorithm for updating snag quantities after wildfire employs geographic information from RAVG, or 

corresponding information derived from the Sentinel data, stratifying by the seven-category severity 

classification, as recoded into four classes for GIS overlay analysis (Table 1). The predicted proportion of 

live trees converted to snags immediately after fire varies by fire severity and tree size. The conversion 

values (“adjustment factors”) were derived from expert opinion (K. Mellen-McLean pers. comm.), and 

are quite similar to values we derived from measurements at the Warner Creek Fire on the Middle Fork 
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Ranger District of the Willamette National Forest (Table 2)(see Brown et al. 2013 concerning the Warner 

Creek Fire).

Table 1. Crosswalk from seven-class version of RAVG or Sentinel-derived fire severity information to 

four-class version used for updating snag densities from GNN data (source: 

T:\FS\Reference\GeoTool\r06\Toolbox\DecAID\Documentation_info\DecAID_Metadata_12202017.xlsx.

RAVG 7 

Class Description RAVG Class used in update

0 outside fire perimeter 0

1

0% basal area (BA) 

loss 0

2 0% - < 10% BA loss 1

3 10% - < 25% BA loss 1

4 25% - < 50% BA loss 2

5 50% - < 75% BA loss 3

6 75% - < 90% BA loss 4

7

90% or greater BA 

loss 4

Table 2. Comparsion of proportions used to update snag information from DecAID using fire severity 

from RAVG and median values of conversion of live trees to snags observed one year after the Warner 

Creek Fire.

RAVG Class Class definition Snag size Class Adjustment 

Factor

Warner 

Creek, one 

year post-fire 

(medians)

Class 1 0% - < 25% basal 

area loss

snag 25-50cm 0.2 0.33

snags >50cm 0.0 0.0

Class 2 25% - < 50% basal 

area loss

snag 25-50cm 0.4 0.45

snags >50cm 0.3 0.2

Class 3 50% - < 75% basal 

area loss

snag 25-50cm 0.7 0.86

snags >50cm 0.6 0.58

Class 4 75% - 100% basal 

area loss

snag 25-50cm 1.0 1.0

snags >50cm 0.9 1.0

To assess snag densities for the Breitenbush River watershed we employed the datasets and methods 

detailed by Kim Mellen-McLean, Regional Wildlife Ecologist, U.S. Forest Service, in documents describing 

the “DecAID Regional Analysis.” The analysis of snag densities prior to the fires of 2017 is contained in 

the file Breitenbush_River_deadwood_analysis_20150702.docx (in Pinyon; contact Steve Acker or Joe 

Doerr for a copy). The individual steps of data processing for the distribution analyses following the 2017 

fires are recorded in the file Fire2017_snag_dens_update_process_log.xlsx, in the folder 

T:\FS\NFS\Willamette\Program\Ecology\GIS\Workspace\DecAID_data2012\2017FireUpdates.

Results and Discussion
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For both the Montane Mixed Conifer Forest and Westside Lowland Conifer-Hardwood Forest habitat 

types, the fires of 2017 affected less than 10% of their total areas within the Breitenbush River 

watershed (Tables 3 and 4). Most of the area within fire perimeters burned at the lowest severity 

captured in the analysis (i.e., less than 25% loss of tree basal area). However, there were several 

hundred acres in both habitat types that burned at the highest severity (i.e., loss of 75% or more of tree 

basal area).

Table 3. Distribution of fire severity due to fires of 2017 within the Montane Mixed Conifer Forest 

habitat type within the Breitenbush River watershed.

RAVG Fire 

Severity Class Basal area loss Acres

Percentage of fire 

area by habitat 

type

Percentage of 

habitat type 

within watershed

1 0% - < 25% 1078 52.7 3.6

2 25% - < 50% 173 8.5 0.6

3 50% - < 75% 179 8.8 0.6

4 75% - 100% 615 30.1 2.1

Total 2044 6.9

Table 4. Distribution of fire severity due to fires of 2017 within the Westside Lowland Conifer-Hardwood 

Forest habitat type within the Breitenbush River watershed.

RAVG Fire 

Severity Class Basal area loss Acres

Percentage of fire 

area by habitat 

type

Percentage of 

habitat type 

within watershed

1 0% - < 25% 922 68.2 2.9

2 25% - < 50% 121 9.0 0.4

3 50% - < 75% 95 7.0 0.3

4 75% - 100% 214 15.8 0.7

Total 1352 4.2

The histograms on the following pages illustrate the estimated density of snags with two lower diameter 

limits, before and after the fires of 2017, for both the Montane Mixed Conifer Forest and the Westside 

Lowland Conifer-Hardwood Forest habitat types (Figs. 1-4; the acronym ‘WHT’ on the histograms refers 

to Wildlife Habitat Type). For the most part, differences between conditions before and after the fires of 

2017 are very minimal to non-existent. The largest change in any one category of snag density was an 

increase in the area with snags with a minimum diameter of 10 inches in the Montane Mixed Conifer 

Forest habitat type, for the category of greater than 36 snags per acre. This category increased from 

13% to 16% of the habitat type in the watershed (Fig. 1). Thus, from the perspective of available tools 

and data, the fires of 2017 caused very little change in the frequency distribution of snag densities in the 

Breitenbush River watershed.
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Fig. 1. Frequency distribution of density of snags with a minimum diameter of 10 inches in the Montane 

Mixed Conifer habitat type in the Breitenbush River watershed, before (upper) and after (lower) fires of 

2017.
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Fig. 2. Frequency distribution of density of snags with a minimum diameter of 20 inches in the Montane 

Mixed Conifer habitat type in the Breitenbush River watershed, before (upper) and after (lower) fires of 

2017.
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Fig. 3. Frequency distribution of density of snags with a minimum diameter of 10 inches in the Westside 

Lowland Conifer-Hardwood Forest habitat type in the Breitenbush River watershed, before (upper) and 

after (lower) fires of 2017.
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Fig. 4. Frequency distribution of density of snags with a minimum diameter of 20 inches in the Westside 

Lowland Conifer-Hardwood Forest habitat type in the Breitenbush River watershed, before (upper) and 

after (lower) fires of 2017.
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Literature Cited

Brown, M. J., J. Kertis, and M. H. Huff. 2013. Natural tree regeneration and coarse woody debris 

dynamics after a forest fire in the western Cascade Range. USDA Forest Service Research Paper 

PNW-RP-592. 50 pp.

Hobson, J. 2017. Using RAVG relative difference Normalized Burn Ratio (RdNBR) burn severity maps and 

Sentinel RdNBR data to generate a regional burn severity grid.

LEMMA. 2015. LEMMA--Landscape Ecology, Modeling, Mapping, and Analysis. 

http://lemma.forestry.oregonstate.edu/ viewed <31-March-2015>

Mellen-McLean, K., B.G. Marcot, J.L. Ohmann, K. Waddell, S.A. Livingston, E.A. Willhite, B.B. Hostetler, C. 

Ogden, and T. Dreisbach. 2012. DecAID, the decayed wood advisor for managing snags, partially 

dead trees, and down wood for biodiversity in forests of Washington and Oregon. Version 2.20. 

USDA Forest Service, Pacific Northwest Region and Pacific Northwest Research Station; USDI Fish 

and Wildlife Service, Oregon State Office; Portland, Oregon. 

http://www.fs.fed.us/r6/nr/wildlife/decaid/index.shtml

U.S. Forest Service. 2015. Post-Fire Vegetation Conditions on the National Forests. 

http://www.fs.fed.us/postfirevegcondition/index.shtml. Viewed <25-Mar-2015>