Objective 2- Earlier in this study, snags were classified into 2 categories; high quality and low quality based on diameter. In this section, we examined nest density and snag diameter to determine if diameter is correlated to nest suitability. We then looked at high quality snag frequency based on treatment type.

Method-

• Snag data was collected in the field using the same protocol as objective 1. • Nest density was determined by comparing the number of nests

observed with snag dbh. • High quality snag frequency was determined by dividing the number of

plots with snags by the total number of plots. This was done for each type of treatment type (thin, reserve, fuelbreak).

Snag Density, Frequency, and Quality in a Mixed Conifer Forest in

The Central Sierra Nevada

Shannon Fairchild, Rob York

University of California, Berkeley, California

Objective 1 Results

.

High Quality density: Thin-3.75/acre, Reserve-6.25/acre, Fuelbreak-

2.22/acre. Low Quality density: Thin-16.56/acre, Reserve-18.44/acre, Fuelbreak-

16.11/ acre The analysis of variance for high quality snags was 0.20. The analysis of variance for low quality snags was 0.92.

Discussion- Snag density varied somewhat by treatment type for both high and low quality snags, but after an analysis of variance was

applied (ANOVA), no difference due to treatment effect were detected. There is a somewhat higher density of snags in reserve plots because snags are not routinely thinned from this type of stand.

Intro-Snags (standing dead trees) are an essential part of forest structure. They provide habitat for cavity nesting birds, squirrels, bats, insects and other species (Bagne, Purcell, & Rotenberry, 2008). Where fire hazard reduction is the objective, snags can be undesirable because they ignite fires in the canopy, potentially increasing fire severity (Stephens & Collins, 2004). However, active fire regimes are necessary for forest health because fire suppression over the last one hundred years has resulted in excess fuel loads which contribute to fire severity (Stephens & Fule, 2005). At Blodgett Forest Research Station (BFRS), a mixed conifer forest near Georgetown, CA (GPS coordinate 38.91161, -120.66027), we examined snag density and frequency by treatment type and quality, as well as nest density. We then compared density and frequency results to an active fire regime forest, Sierra San Pedro Martir (SSPM) in Northern Mexico. SSPM was chosen because it has not had fire suppression like most forests in North America and acts as a “natural” control (Stephens, 2004).

Objective 2 Results Objective 3- We compared overall density and frequency of snags in BFRS with the SSPM snag data from 1998. This year was chosen because it predates known fire suppression in SSPM. SSPM has an active fire regime. Frequency was also analyzed based on treatment type, with thinned and fuelbreak stands combined into one category. This was done to take into account the effect of harvesting on snag density. Method- • Snag data collected in the field using the same method as objective

1 and 2. • Overall snag density was determined based on the average number

of snags per acre. • Snag frequency was determined based on the number of plots with

snags divided by the total number of plots analyzed. Results

Objective 1- In this study, snag density was determined by first collecting snag data in the field. The data was then analyzed based on treatment type. Snags were divided into 2 size categories: >16” dbh (diameter at breast height) and 8-16”dbh. Snags smaller than 8”dbh were excluded from this study as their information was not collected in this year’s field inventory.

Treatment Types Fuelbreak Reserve Thin Method • Data collection protocol at BFRS. Organized by compartment and

plot.

1) snags >8” dbh and within 32.7’ of plot center were recorded 2) height measured with hypsometer 3) hardness, top, woodpeckers, nest, years dead, % bark recorded

Density determined by number of snags sampled per plot. Each plot is 1/10 of an acre. The number of snags per plot was multiplied by 10 to determine snags per acre density. Snags were then classified as high (>16” dbh) or low (8-16” dbh) quality.

Frequency determined by averaged percent of plots with at least one high quality snag. HQ snags are more valued for nest habitat.

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dbh >16" dbh 8-16"Sn

ag D

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Snag size (diameter at breast height)

Snag Density based on Treatment Type and Snag Size

Thin

Fuelbreak

Reserve

Works Cited

Bagne, K. E., Purcell, K. L., & Rotenberry, J. T. (2008). Prescribed fire, snag population dynamics, and avian nest site selection. Forest Ecology and Managment, 99-105. Meyer, M. D., Kelt, D. A., & North, M. P. (2005). Nest trees of Northern Flying Squirrels in the Sierra Nevada. Journal of Mammology, 275-280. Stephens, S. L. (2004). Fuel loads, snag abundance, and snag recruitment in an unmanaged Jeffrey pine–mixed conifer forest in Northwestern Mexico. Forest Ecology and Managment, 103-113. Stephens, S. L., & Collins, B. M. (2004). Fire Regimes of Mixed Conifer Forests in the Northen Central Sierra Nevada at Multiple Spatial Scales. Northwest Science, 12-23. Stephens, S. L., & Fule, P. Z. (2005). Western Pine Forests with Continuing Frequent Fire Regimes: Possible Reference Site for Managment. Journal of Forestry, 357-362. Stephens, S. L., & Moghaddas, J. J. (2005). Fuel treatment effects on snags and coarse woody debris in a Sierra Nevada mixed conifier forest. Forest Ecology and Management, 53-64. Walter, S. T., & Maguire, C. C. (2005). Snags, Cavity Nesting Birds and Silviculture Treatmens in Western Oregon. Journal of Wildlife Management, 1578-1591.

Special Thanks to

Drew Fitzpatrick Kyle Keller Allegra Mautner

As well as all the staff and crew at BFRS

y = 1.1895x + 12.609 R² = 0.0972

0

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0 5 10 15

Dia

me

ter

At

Bre

ast

He

igh

t (i

nch

es)

Number of Nests

Nest Density and DBH

Nest

19%

81%

HQ Snag Frequencies- Thin

plots with HQ snags

Plots without HQ snags

28%

72%

Reserve

plots with HQ snags

plots without HQ snags

23%

77%

Fuelbreak plots with HQ snags

plots without HQ snags

21.03

9.76

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Acr

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Overall Snag Density

BFRS

SSPM

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Snag Frequency

BFRS-thin BFRS-reserve SSPM

The largest number of nests, 12, was observed in a 26.8” dbh snag.

The largest snag dbh recorded, 47”, had zero nests.

The majority of snags, regardless of dbh, had zero nests.

The R² value for nest density and dbh was 0.0972.

The highest frequency of snags occurred in reserve stands (28%).

The lowest frequency of snags occurred in thinned stands (19%).

Discussion- Nest density appears to be correlated with diameter, although there are many other factors that influence nest site selection. The

surrounding habitat and tree species are also other factors that are important for nesting species. The

higher frequency of snags in reserve stands suggests that there is a greater occurrence of high quality trees found in reserves that could be used as nesting habitat, but more study is needed.

Compared to SSPM, BFRS has greater density.

BFRS 21.03 snags/acre

SSPM 9.76 snags/acre.

Compared to SSPM, BFRS had lower overall frequency.

Taking treatment type into account- BFRS had 52% thin, 78% Reserve frequency

SSPM had 65% frequency

Discussion- The results of this study suggest that, even following frequent harvests that removed lower vigor trees, BFRS has an overabundance of snags compared to a forest with active fire regimes.

Conclusions- We found that density and frequency did not vary significantly by treatment type. We also found that nest density was correlated to dbh, with larger dbh snags showing greater nest density. Reserve stands may be more suitable for nest habitat but more study needs to be done. Compared to SSPM, BFRS has greater overall density, but less frequency. This suggests that, even following frequent harvests that removed lower vigor trees, BFRS has an overabundance of snags compared to a forest with active fire regimes. Managers seeking to balance wildlife and fire hazard reduction objectives may consider recruiting fewer but higher quality snags (i.e. larger) as a management objective.