Created Wildlife Tree Monitoring Report: Trends and Future Recommendations

Travis J. Woolley1

David C. Shaw1

Joan C. Hagar2

July 13, 2007

1 Department of Forest Science - Oregon State University2 USGS – Forest and Rangeland Ecosystem Science Center

Project was accomplished through a cost reimbursable agreement between Oregon State University and the Central Cascades Adaptive Management Partnership

Table of Contents

Executive Summary...........................................................................................................1

Wildlife Tree Monitoring Trends.....................................................................................2

Introduction.....................................................................................................................2

Assumptions and scope of inference...............................................................................2

Mortality of created wildlife trees...................................................................................3

Bird use of created wildlife trees.....................................................................................4

Foraging.......................................................................................................................4Cavities........................................................................................................................7

Inoculation treatments...................................................................................................10

Recommendations for Database Design and Data Collection.....................................11

Data collection...............................................................................................................11

Variable construction.................................................................................................11Quality control...........................................................................................................11

Database formatting and data entry...............................................................................12

Quality control...........................................................................................................12Formatting..................................................................................................................12Metadata....................................................................................................................13Additional database variables....................................................................................13

Attachments......................................................................................................................17

Wildlife Tree Creation Literature......................................................................................17

Executive Summary

The goal of the project and the following report was to assess the efficacy of wildlife tree creation to provide wildlife habitat in harvested units. A database with over 1823 trees monitored from 2002-2006 on the McKenzie River Ranger District, Willamette National Forest, was used for the analysis.

Sampling design limitations constrained our scope of inference and did not allow for statistical analyses. Therefore, trends observed in the data are described, but these trends represent only those trees sampled, and may or may not characterize the population of created wildlife trees on the district. Findings are based on trees in clearcuts. It is unknown how similar treatment to trees in other types of harvest units would be. In addition, saw-topped and blasted treatments had the longest treatment history, and results from the earliest time periods are biased towards them.

Due to sampling design limitations, mortality estimates are likely lower than actual rates. However, they do indicate the effectiveness of more aggressive treatments, such as saw-topping, blasting, and girdling, in killing trees. Girdling treatments showed a slightly lower rate of mortality, requiring several more years before reaching at least 80% mortality. Inoculation only treatments showed very low mortality among created trees.

Wildlife tree longevity (i.e., fall down rates) could not be assessed due to limitations in sampling design.

By year 5 following treatment, approximately 80% of trees were being used by birds for foraging, regardless of treatment. Although there was a high degree of variation between stands, new foraging continued to increase over time. Blasted trees had a higher rate of foraging use than other trees.

No potential nest cavity excavation was observed until year 7 following treatment, regardless of the type of treatment. Blasting and saw-topping treatments incurred the most potential nest cavity use by birds, however trees treated by either girdling or inoculation also had cavities. Potential nest cavities were not observed until year 9 and were observed most frequently in blasted trees. No trees inoculated with fungus were found to have nesting cavities within 9 years. By year 15, 60% of trees created by blasting were used for nest cavities.

Although inoculation treatments are of increasing interest to managers, we were unable to assess the effectiveness of this treatment for increasing or accelerating decay processes within trees. Recommendations for future analysis of inoculation treatments are given.

Recommendations for future monitoring of created wildlife trees include improved sampling design, as well as improved quality control and assurance of data collection and database management. Upfront sampling design is essential to future monitoring projects

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Wildlife Tree Monitoring Trends

Introduction

The McKenzie River Ranger District, Willamette National Forest has developed a database for an adaptive management project monitoring created wildlife trees following harvest. They are interested in answering questions regarding effectiveness of treatment methods, indicated by mortality and fall down rates, and bird use (both foraging and nesting) of created wildlife trees. In this report we describe and document trends found in the data for both mortality and bird use of created wildlife trees. Recommendations are suggested for future monitoring and analyses. We also present a proposal for a re-sampling approach that would permit the use of inferential statistics to address management questions that would add value to and/or strengthen the results shown here.

The database used for this descriptive analysis consists of wildlife trees created using several methods. There are multiple goals for each of these methods, or “treatments”, to maximize the usefulness to wildlife (i.e., produces decay patterns that optimize utility and longevity of habitat).Some methods result in rapid mortality, while others provide a slow mortality over time aimed at longevity of habitat availability. The methods used to create wildlife trees (snags) were: blasting, saw-topping, girdling (above base of crown), fungal inoculation, and combinations of saw-topping or girdling with fungal inoculations. The database contains 6994 wildlife tree records and the associated variables recorded at the time of treatment. A subset (1823) of those trees was revisited following treatment to collect monitoring data. Monitoring occurred from 1 to 15 years following treatment, but individual trees were not visited more than once.

Many of the wildlife tree records were not valid for analysis for several reasons (see Recommendations for monitoring). Therefore, the following trends are based on 951 created wildlife trees monitored in clear-cut units. In addition to omitting some of the individual tree records for use in analyses, we were not able to use several variables due to inconsistencies in data collection and/or difficulty of interpretation (see Recommendations for monitoring).

We have limited this report to findings of mortality and bird use (both foraging and nesting) of created wildlife trees as a function of treatment and time since treatment.

Assumptions and scope of inference

The field data was not collected randomly and has a bias towards standing trees due to collection methods. Therefore, our scope of inference for the following trends is limited to only those trees that were sampled. We cannot address questions pertaining to fall down rates for created wildlife trees. It is also important to note that the mortality rates reported here are possibly biased toward lower rates than due to a bias in sampling towards standing trees.

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The structure of the database (i.e., treatments, time, and monitored variables) is suitable for statistical comparisons of desired variables across treatments. However, due to the sampling design we were unable to extrapolate those results any farther than the trees monitored. Therefore, we do not report any statistical quantitative findings. (For further sampling and analysis recommendations see Proposed Sampling and Analysis Plan).

When interpereting the following trends it is important to note that individual trees were not visited more than once. Therefore a time series does not exist, rather a chronosequence of time since creation is presented. For example, trees represented by data in year 2 (Figure 1) are not the same trees as represented by data in year 11.

Mortality of created wildlife trees

Patterns of mortality of created wildlife trees over time following treatment were different based on treatment used. Saw-topped and blasted treatments were the most successful at producing snags within the first 5 years. During this period approximately 80% of the created wildlife trees monitored died (Figure 1) within the first 5 years.

Figure 1. Percent mortality of created wildlife trees at varying times since treatment for three similar treatments.

Girdling treatments showed a slightly lower rate of mortality (Figure 1), requiring several more years before reaching at least 80% mortality. In contrast, inoculation-only treatments showed very low mortality among created trees (Figure 2). No substantial mortality occurred in inoculated trees until 9 years following treatment. Combination treatments (girdled or saw-topped with fungal inoculation) did not appear to have different mortality rates than either girdling or saw-topping alone 4 years following

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treatment. However, it is important to note that the objective of inoculating in combination with these treatments was not to increase mortality, but to alter decay patterns within the tree to encourage faster, more effective nest excavation compared to other treatments. Further investigation of decay presence and spread is necessary to determine the success of this objective.

Figure 2. Percent mortality of created wildlife trees at varying times since treatment for treatments that include fungal inoculation.

Bird use of created wildlife trees

Foraging

Use of created wildlife trees (live and dead) by birds for foraging showed very similar trends across treatments (Figure 3). Percent of created trees used for foraging increased rapidly in the first 4 years following treatment (up to ~90% of trees used in year 4). A slight decrease in foraging was evident before approaching 100% of trees used for foraging 10 to 11 years following treatment. We hypothesize that the apparent sudden drop in cumulative foraging in 5-8 years following treatment may be an artifact of bark sloughing off of trees. The loss of bark may make it difficult for observers to estimate foraging use accurately.

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When examining new foraging activity (foraging occurring within the last year) a linear relationship was found (Figure 4). Over time, foraging use steadily increased to approximately 80% by year 10. It is important to note however, there are several interactions that are not accounted for by this simple linear relationship. At the stand level, foraging use by birds showed a general increasing trend over time (Figure. 4). This trend began to level off as trees approached 15 years since treatment. There was a large degree of variability across stands (Figure 5). We were not able to detect patterns associated with foraging use and elevation, or foraging use and tree size.

Figure 3. Percent of created wildlife trees used by birds for foraging at varying times since treatment for all 6 treatments.

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Figure 4. Percent of created wildlife trees used by birds for new foraging over time for all treatments combined.

Figure 5. Percent of created wildlife trees used by birds for foraging over time for individual stands illustrating the high degree of variability between stands over time.

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Cavities

Use of created wildlife trees for cavity excavation did not occur within any treatment for the first 5 years following creation (Figure 6). Nest cavities were not detected until year 9 following treatment (Figure 7). No trends among treatments are evident for either cavities as a whole or nesting cavities alone. Many of the treatments are not older than 5-9 years, so trends of bird use are only evident for the older treatments (blasting and saw-topping, and to a lesser degree girdling). In year 15 following treatment, nearly 60% of all trees created by blasting were used for potential nesting cavities (Figure 7).

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Figure 6. Percent of created wildlife trees with foraging and nesting cavities at varying times since treatment for all 6 treatment types.

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Figure 7. Percent of created wildlife trees with nesting cavities at varying times since treatment for all 3 treatment types. Trees in the remaining 3 treatments (inoculation treatments) had no evidence of cavity nesting.

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Inoculation treatments

Inoculation treatments involved the use of several fungal species to initiate stem decay in leave trees following harvest. Some trees were inoculated in combination with girdling or saw-topping. Inoculation-only treatments were done with one, two, or three species of fungus per tree (Table 1). However, only 2 fungal species (Fomitopsis cajanderi and Phellinus pini) were used as inoculum frequently enough to draw any meaningful patterns from (Table 1). We suggest that if further inoculation treatments are planned, and there is a need to address questions regarding effectiveness of the treatment, that a plan be developed regarding the types and numbers of fungal species to use, and the number of trees inoculated with each fungal species. We also suggest that, to yield meaningful results, the focus should be on a relatively low number of fungal species (2-3), and that combination treatments involving multiple species are also kept to a minimum. Another confounding factor to consider is the number of dowels used in inoculation. Using an equal number of dowels across fungal treatments would balance the statistical design to enable a more rigorous comparison of inoculation techniques.

No trees treated with Fomitopsis cajanderi had died up to 9 years following treatment. No mortality of trees treated with Phellinus pini was seen until years 7 (2), 8 (1), and 9 (2). Proportionally, trees treated with Phellinus pini exhibited more stress in year 9 than trees treated with Fomitopsis cajanderi. No differences in foraging activity were evident between trees inoculated with these two fungal species. No trees inoculated with either fungus were found to have nesting cavities 9 years following treatment.

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Recommendations for Database Design and Data Collection

Recommendations for specific variables are summarized in Table 1, which describes problems associated with several of the database variables. Below are examples of these concerns framed by the aspect of the monitoring process in which problems arose and where improvements could be made.

Data collection

Variable construction

When constructing a variable for monitoring, the ease of interpretation is an important consideration. For example, the variable canopy cover as collected for this database, is difficult to interpret. When trying to understand the effects of canopy cover on bird use of individual wildlife trees one would need a single discrete estimate for each individual tree. In the database there is a canopy cover classification for 4 separate quadrants using very broad (low precision) categories. To derive a single estimate for an individual tree, the estimates for the 4 separate quadrants would have to be averaged. However, with such broad categories a large portion of the information would be lost. Thus, due to this low precision, this variable may not prove significant in a statistical analysis, when in fact it may have an affect on bird use. A recommendation would be to measure this variable on a whole tree basis in 5-10% increments. The use of 4 quadrants is still acceptable, as long as the precision of the % cover is within 5%.

Quality control

One of the concerns with the database is the lack of quality control, specifically with data collection. The consistency with which the data is collected is extremely important in the value of each individual tree to the database and any subsequent analyses. Generally these issues revolved around the consistency with which the variable(s) was recorded and whether it was recorded or left blank.

The precision of variables such as diameter at breast height (DBH), treatment height, the number of branches left, etc. were not consistently recorded, ranging from measurements to the nearest tenth of an inch to whole numbers for DBH, and from ranges (e.g., 40-50 ft.) to broad categories such as “greater than” estimates of treatment height. The number of branches remaining following treatment was recorded in several ways, including discrete numbers of branches, “greater than” estimates, and percentages.

Another recommendation would be that all variables for a given tree have something recorded in them, rather than leaving them blank, especially for continuous variables, such as % bark loss. It is hard to determine, after the fact, whether a given variable for a tree should be a zero or the actual value was not recorded.

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It would also be useful for monitoring observers to follow several key requirements to ensure proper and consistent data collection. First, monitoring observers should familiarize themselves (possibly through training) with sampling protocol, specifically definitions and variable codes. For example, decay classes (when recorded) were not consistent with % bark loss recorded. A decay class 2 snag should not have any significant bark loss, although many class 2 snags were recorded with 20% bark loss. Secondly, to ensure data quality, data sheets should be checked for completeness (i.e., all variables should be measured and recorded properly, for example DBH should always be recorded on live trees). Many times the proper categorical code is not used, making that individual record unavailable for analysis. Having frequent quality checks will help to hold contractors responsible for the quality of their data collection.

For relocating trees for future monitoring efforts, monitoring contractors should be required to have a GPS unit and obtain coordinates for each tree. In cases where coordinates are unattainable, a recording of location notes as exact as possible (e.g., 150 ft. from NW corner of stand @ 180°) should be required.

Database formatting and data entry

Quality control

Issues that arose during quality control measures were: missing variables such as field and monitoring observer, inconsistent entering of codes (e.g., hc as opposed to HC), use of letters in combination with continuous number variables (e.g., 3B for 3 branches), and blanks as opposed to N/A, or N/, or 0. These issues can be resolved by putting in place a system to ensure consistent data entry, and what should or should not go in a column.

Implementation of an outlined quality control process would also be extremely useful following data entry. One option would be to enter the data twice and use a cross-referencing program to detect anomalies between the two data sets. This process is used by the Permanent Study Plot Program (H.J. Andrews Experimental Forest) for their long-term monitoring of trees for growth and mortality. This process could easily be adapted to this database. Re-checking data following data entry by sorting columns individually and inspecting each is also an option. This may be more time consuming than desired and increase project costs.

Formatting

Database formatting is also a concern for future analysis. It is recommended that data that can have multiple values for a single attribute (e.g., inoculum species, insects, decay, foraging type, etc.) be split into the number of columns necessary to accommodate the number of attributes. For example, if there are at most 3 fungal species inoculated into trees, then there should be three columns in the database entitled Inoculum Species1, Inoculum Species2, and Inoculum Species3. This will prevent this step from having to be done during data analysis.

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Metadata

Database metadata exists, but in several formats including both descriptive tables and word processing documents. Descriptive tables do not include code information for variables and only give data formatting information from Microsoft Access. Metadata should be formalized into a database file format (.dbf) to be included as a database table in the Microsoft Access project file (.mdb) for availability when using the database. Included in the updated version of the WLTMondb, are two database files, WLTDB_Format and WLTDB_Codes. The first table is a format table that describes the format of the variables in the database. The second table contains all the codes used for each variable and a definition and plausible values for each (incomplete due to lack of variable definitions). This metadata style was adopted from the H.J Andrews information management system and is based on current information management practices.

For further information regarding quality control, metadata, and general database protocol questions contact Don Henshaw (don.henshaw@oregonstate.edu; 541-750-7335) or Suzanne Remillard (suzanne.remillard@oregonstate.edu; 541-758-8767) with the H.J. Andrews Experimental Forest.

Additional database variables

We suggest adding the type of harvest treatment as a variable to the database, as well as some type of vegetation zone or plant association group variable (see Attachments). There are also a number of variables at the end of the database that could prove useful, but are not currently being used.

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Table 1. Variables in the created wildlife tree database that have one or more problems due to design, data collection, and/or data entry. Recommended solutions are possible steps that can be taken to ensure future data quality.Database Variable Problem or Issue Recommended Solution(s)

Decay Class Inconsistent with protocol; missing values

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality control

inspection of field data and/or data entry

Snag Distribution Missing values Quality control inspection of field data and/or data entry

Distance to Edge Recorded improperly; missing values; possible lack of precision

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality control

inspection of field data and data entry

% Canopy Cover Lack of precision; not easily interpreted

This variable should be reconstructed with greater level of precision that will provide a single canopy cover estimate for

an individual tree

Treatment Height Recorded as “greater than ”; missing values

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality control

inspection of field data and/or data entry

Branches Initial Recorded as both % and number (with “B” included); missing values

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality control

inspection of field data and/or data entry

ElevationMissing values (due to lack of GPS

unit or inability to acquire coordinates)

Use Geographic Information Systems to obtain and assign elevation values for each stand in the database

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Table 1. ContinuedDatabase Variable Problem or Issue Recommended Solution(s)

Diameter at Breast Height

Recorded with varying levels of precision (range, “greater than ”, nearest inch, tenth of an inch);

missing values

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality

control inspection of field data and/or data entry

Inoculum Species (# of dowels)

Combination of multiple species and number of dowels in same column is

problematic for analysis

Create separate columns for each species used and a separate column for number of dowels used in both data collection

and in the database

Aspect Inconsistently recorded; missing values

Quality control inspection of field data and data entry; This variable may not provide information useful for analysis, but

provides a record for future location of treatment

Monitoring GPS Coordinates

Missing values; values for northing and easting recorded in the same

column

Require monitoring observers use a GPS unit and if coordinates are unattainable make consistent notes on tree

location; Create separate columns for each set of coordinates

Insect Presence Multiple insect codes entered in the same column Create separate columns for each insect code encountered

Decay Presence Multiple decay codes entered in the same column Create separate columns for each decay code encountered

Damage/DiseaseMultiple damage/disease codes

entered in the same column; some notes, some codes

Create separate columns for each damage/disease code encountered; Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol;

Quality control inspection of field data

% Bark Loss Recorded as ranges and as continuous from 0-100%

Write and implement a rigorous monitoring protocol; Training of monitoring observers with protocol; Quality

control inspection of field data

Foraging type Multiple foraging codes entered in the same column Create separate columns for each foraging code encountered

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Table 2. The number of trees per inoculation treatment (fungal species) over time illustrating inconsistent and unbalanced design. This does not include inoculations of multiple fungal species, or any combinations of inoculation and saw-topping or girdling treatments. Numbers in bold indicate adequate sample sizes for analysis and comparisons between inoculation treatments.

Time Since Treatment (years)Inoculum species

#trees 1 2 3 4 5 7 8 9 11 12 15

FC 60   0 4 0 0 0 16 32 8 0 0 0

FC2 6 2 3 1 0 0 0 0 0 0 0 0

FC5 9 0 0 4 5 0 0 0 0 0 0 0

FP 10   0 4 1 5 0 0 0 0 0 0 0

FP2 7 2 5 0 0 0 0 0 0 0 0 0

FP5 7 0 0 2 5 0 0 0 0 0 0 0

PP 106   0 2 0 3 19 32 32 14 5 3 1

PP2 4 1 3 0 0 0 0 0 0 0 0 0

PP5 10 0 0 4 6 0 0 0 0 0 0 0

SS 1   0 1 0 0 0 0 0 0 0 0 0

SS2 5 1 4 0 0 0 0 0 0 0 0 0

SS5 5 0 0 1 4 0 0 0 0 0 0 0

Total 230 6 26 13 28 19 48 64 22 5 3 1

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Attachments

The following will be provided to the MRRD in electronic format via CD or DVD.

1. Copy of report to district.2. Copy of WLTDB including metadata files3. Endnote library containing literature relevant to wildlife tree creation.4. Pdf’s of relevant literature5. ArcGIS files consisting of stand boundary layers, digital elevation models, GPS points of

created/monitored wildlife trees, and plant association data.

Wildlife Tree Creation Literature

Agee, J. K., and M. H. Huff. 1987. Fuel succession in a western hemlock/Douglas-fir forest. Canadian Journal of Forest Research 17:697-704.

Aubry, K. B., and C. M. Raley. 2002. The Pileated Woodpecker as a KeystoneHabitat Modifier in the Pacific Northwest. USDA Forest Service Report PSW-GTR-181.

Baker, F. A., S. E. Daniels, and C. A. Parks. 1996. Inoculating trees with wood decay fungi with rifle and shotgun. Western Journal of Applied Forestry 11:13-15.

Bate, L. J., E. O. Garton, and M. J. Wisdom. 1999. Estimating Snag and Large Tree Densities and Distributions on a Landscape for Wildlife Management. USDA Forest Service Pacific Northwest Research Station. Report PNW-GTR-425.

_____. 2002. Sampling Methods for Snags and Large Trees Important to Wildlife. USDA Forest Service. Report PSW-GTR-181.

Boleyn, P., E. Wold, and K. Byford. 2002. Created snag monitoring on the Willamette National Forest. USDA Forest Service. Report PSW-GTR-181.

Brandeis, T. J., M. Newton, G. M. Filip, and E. C. Cole. 2002. Cavity-nester habitat development in artificially made Douglas-fir snags. Journal of Wildlife Management 66:625-633.

Brown, T. K. 2002. Creating and maintaing wildlife, Insect, and fish habitat structures in dead wood. Report PSW-GTR-181.

Bull, E. L. 1983. Longevity of snags and their use by woodpeckers. Pages 64-67 in J. W. Davis, andet al., editors. Snag habitat management: proc. symposium, Flagstaff, 1983. USDA Forest Service, General Technical Report, RM-99.

_____. 1987. Ecology of the pileated woodpecker in northeastern Oregon. Journal of wildlife Management 51:472-481.

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_____. 2002. The value of coarse woody debris to vertebrates in the pacific northwest. USDA Foest Service. Report PSW-GTR-181.

Bull, E. L., and J. E. Hohmann. 1993. The association between Vaux's swifts and old growth forests in northeastern Oregon. Western Birds 24:38-42.

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Bunnell, F. L., L. L. Kremsater, and E. Wind. 1999. Managing to sustain vertebrate richness in forests of the Pacific Northwest: relationships within stands. Environmental Reviews 7:97-146.

Bunnell, F. L., E. Wind, M. Boyland, and I. Houde. 2002c. Diameters and heights of trees with cavities: Their implications for management. USDA Forest Service. Report PSW-GTR-181.

Carey, A. B. 1989. Wildlife associated with old-growth forests in the Pacific Northwest. Natural Areas Journal 9:151-162.

_____. 1995. Sciurids in Pacific Northwest managed and old-growth forests. Ecological Applications 5:648-661.

Carey, A. B., and H. R. Sanderson. 1981. Routing to accelerate tree-cavity formation. Wildlife Society Bulletin 9:14-21.

Chambers, C. L., T. Carrigan, T. E. Sabin, J. C. Tappeiner, and W. C. McComb. 1997. Use of artificially created Douglas-fir snags by cavity-nesting birds. Western Journal of Applied Forestry 12:93-97.

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Chambers, C. L., W. C. McComb, and J. C. Tappeiner. 1999. Breeding bird responses to three silvicultural treatments in the Oregon coast range. Ecological Applications 9:171-185.

Cline, S. P., Berg, and E. M. Wight. 1980. Snag characteristics and dynamics in Douglas-fir forest, western Oregon. Journal of wildlife Management 44:773-786.

Cline, S. P., and C. A. Phillips. 1983. Coarse woody debris and debris-dependent wildlife in logged and natural riparian zone forests - a western Oregon example. Pages 33-39 in J. W. Davis, andet al., editors. Snag habitat management: proc. symposium, Flagstaff, 1983. USDA Forest Service, General Technical Report, RM-99.

Dahms, W. G. 1949. How long do ponderosa pine snags stand? USDA Forest Service - Pacific Northwest Forest and Range Experiment Station. Report PNW-57.

Farris, K. L., E. O. Garton, P. J. Heglund, S. Zack, and P. J. Shea. 2002. Woodpecker foraging and the successional decay of ponderosa pine.

Farris, K. L., M. J. Huss, and S. Zack. 2004a. The role of foraging woodpeckers in the decomposition of ponderosa pine snags. The Condor 106:50-59.

_____. 2004b. The role of foraging woodpeckers in the decomposition of ponderosa pine snags. Condor 106:50-59.

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Foster, D. R., D. H. Knight, and J. F. Franklin. 1998. Landscape patterns and legacies resulting from large, infrequent forest disturbances. Ecosystems 1:497-510.

Garber, S. M., J. P. Brown, D. S. Wilson, D. A. Maguire, and L. S. Heath. 2005. Snag longevity under alternative silvicultural regimes in mixed-species forests of central Maine. Canadian Journal of Forest Research 35:787-796.

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Harmon, M. E. 2002. Moving towards a new paradigm for woody detritus management. USDA Forest Service. Report PSW-GTR-181.

Harmon, M. E., J. F. Franklin, F. J. Swanson, P. Sollins, S. V. Gregory, J. D. Lattin, N. H. Anderson, S. P. Cline, N. G. Aumen, J. R. Sedell, G. W. Lienkaemper, K. Cromack, and K. W. Cummins. 1986. Ecology of coarse woody debris in temperate ecosystems. Advances in Ecological Research 15:133-302.

Hayes, J. P., S. H. Schoenholtz, M. J. Hartley, G. Murphy, R. F. Powers, D. Berg, and S. R. Radosevich. 2005. Environmental consequences of intensively managed forest plantations of the Pacific Northwest. Journal of Forestry 103:83-87.

Kennedy, R. S. 2005. Dead wood dynamics and relationships to biophysical factors, forest history, ownership, and management practices in the coastl province of Oregon, USA. Oregon satte University, Corvallis.

Korol, J. J., M. A. Hemstrom, W. J. Hann, and R. A. Gravenmier. 2002. Snags and down wood in the interior Columbia basin ecosystem management project. USDA Forest Service. Report PSW-GTR-181.

Lewis, J. C. 1998. Creating snags and wildlife trees in commercial forest landscapes. Western Journal of Applied Forestry 13:97-101.

Mannan, R. W., E. C. Meslow, and H. M. Wight. 1980. Use of snags by birds in Douglas-fir forests, western Oregon. Journal of Wildlife Management 44:787-797.

Martin, K., K. E. H. Aitken, and K. L. Wiebe. 2004. Nest sites and nest webs for cavity-nesting communities in interior British Columbia, Canada: nest characteristics and niche partitioning. The Condor 106:5-19.

Mazurek, M. J., and W. J. Zielinski. 2004. Indiviudal legacy trees influence vertebrate wildlife diversity in commercial forests. Forest Ecology and Management 193:321-334.

Mellen, K., B. G. Marcot, J. L. Ohmann, K. L. Waddell, E. A. Willhite, B. B. Hostetler, L. S.A., and C. Ogden. 2002. DecAID: A decaying wood advisory model for Oregon and Washington. USDA Forest Service. Report PSW-GTR-181.

Morrison, M. L., M. F. Dedon, M. G. Raphael, and M. P. Yoder-Williams. 1986. Snag requirements of cavity-nesting birds: are USDA Forest Service guidelines being met? Western Journal of Applied Forestry 1:38-42.

Morrison, M. L., and M. G. Raphael. 1993. Modeling the dynamics of snags. Ecological Applications 3:322-330.

Newton , I. 1994. The role of nest sites in limiting the numbers of hole-nesting birds: a review. Biological Conservation 70:265-276.

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Ohmann, J. L., W. C. McComb, and A. A. Zumrawi. 1994. Snag abundance for primary cavity-nesting birds on non-federal forest lands in Oreogn and Washington. Wildlife Society Bulletin 22:607-620.

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