Effect of silvicultural and Effect of silvicultural and prescribed fire treatments on prescribed fire treatments on

coarse woody debris dynamics in coarse woody debris dynamics in a sierran old growth mixed-conifer a sierran old growth mixed-conifer

forest.forest.

Jim Innes and Malcolm NorthUSDA-PSW Sierra Nevada Research

Center Davis, California

Coarse Woody Debris (CWD) in the Sierra Nevada

• Important habitat for small to mid-sized mammals particularly during snow cover.

• Long duration fire fuels.• Knowledge gap concerning

management/restoration guidelines for CWD in Sierra Nevada.– Guidelines are based on fire

suppressed forest structures (for example, The CASPO Report).

Study Site – Teakettle Experimental Forest

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18, 4 hectare plots

• Patterson Mountain, California

• Old growth mixed- conifer forest.

• 2000 m elevation.

Methods• Full Factorial Experiment with 3 replicates:

– Prescribed fire and 2 levels of cutting:• Shelterwood (Low thinning) > 25 cm leaving 22 trees per hectare.

• California spotted owl cut (CASPO) harvest from 25 cm to 76 cm.

• Here we are using a plot from each treatment and 3 controls.

• Mapped all logs > 30 cm small-end-diameter within each 4 ha plot.

• Decay classes 1 – 4. • Analysis: t-test and Ripley’s K function, alpha = .05

HypothesesThin no burn treatment:

– Increase the per hectare plot density, volume and mass of CWD.

– Decrease mean piece large-end-diameter and volume.

Burning in combination with thinning:

– Decrease per hectare plot density, volume and mass of CWD.

– Decrease mean piece-volume and mean piece large-end-diameter.

Burning alone.

– Increase mean piece-volume and mean piece large-end-diameter.

Results - Thin no burn treatment

1. Will increase the per hectare plot density,

– Yes, density 39% in the CASPO and 48 % in the shelterwood.

volume (m3 ha-1) and mass (Mt ha-1) of CWD.

– No, CASPO volume 10% and Mass 4%.

– Shelterwood volume 25% and mass 9 % .

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Results - Thin no burn treatment

2. Thinning alone will decrease mean piece large-end-diameter (cm) and volume (m3) .

– CASPO mean piece large-end-diameter 21% (16 cm, (p=0.0001).

– Mean piece volume 44% (2.1 m3, p=0.004).

– Shelterwood mean piece large-end-diameter 19% (13.4 cm, p=0.0001).

– Mean piece volume 60% (2.9 m3, p=0.0001).

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Results - Thin and burn treatment1. Decrease in per hectare plot

density, volume (m3 ha-1) and mass (Mt ha-1).

– CASPO Density 38%, volume 70% and mass 69%.

– Shelterwood by 26%, volume 39% and mass 19%.

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Results - Thin and burn treatment

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2. Decrease mean piece-volume (m3) and mean piece large-end-diameter (cm).

•CASPO 60% mean piece-volume (2.2 m3, P=.0001).• 29% mean piece large-end-diameter (22.4 cm, p=.0001).

•Shelterwood 56% mean piece-volume (3.2 m3, P=.007). • 24% Mean piece large-end-diameter (20.5 cm, p=.0001).

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Results – Burn only treatment

• Increase mean piece volume (m3) and mean piece large-end-diameter (cm).– Mean piece volume by

50% (2.5 m3, p=0.003) and mean piece large-end-diameter 12% (8 cm, p=.03).

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Decay Dynamics

• Cut only• in lower decay classes

due to logging slash.

• Cut and burn• in lower decay classes

from slash and in higher decay class due to removal by fire.

• Burn plots - higher decay

classes due to removal by fire.

Spatial Patterns – Control plots

• Variability among plots.

• Control plot 2 random clustering possibly due to a spot fire in 1917.

- Suggests past fires may produce long lasting legacy patterns.

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Control 2Clustered

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Spatial Patterns – Treated plots Shelterwood

Unburned shelterwood

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Pretreatment

Burned shelterwoodPretreatment

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Pretreatment Unburned CASPO

Burned CASPOPretreatment

Clustered

Random

Regular

• No trend in spatial patterns with treatments.• or in significance of clustering with treatment.

Summary• Cut and cut and burn treatments –

1. Change in quality of CWD from fewer larger pieces to a greater number of smaller pieces.

2. Average diameter 16 cm in cut only.3. Average diameter 21 cm in cut and burn plots.4. Shift in decay to the lower decay classes.

• Burn only – 1. Less of a diameter reduction relative to the cut, cut and burn plots

(8 cm) due to no inputs of smaller diameter logs.

• Variation in topography, aspect and past fire history likely plays a large role in CWD dynamics.

• Spatial patterns do not show a trend with cutting and or burning treatments and fall within pretreatment spatial variability.

Recommendations for Managers

• Contact– Jim Innes – jinnes@fs.fed.us

– http://teakettle.ucdavis.edu

• Cutting and cutting and burning alter the structure of CWD more so than fire alone.

• Reductions in log diameters may impact habitat availability for some species. Leaving some larger logs may mitigate diameter decreases after cutting and burning.

• Spatial patterns do not appear to be altered by the treatments beyond the pretreatment range of variability at the studied scale.