Variable Thinning Using Historical Stand Structure Data to Create Fire-Resilient Forests and Enhance...
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Variable thinning using historical stand structure data to create fire-resilient forests and enhance
ecosystem services in a changing climateEric Knapp – USFS Pacific Southwest Research Station Roger Bales – Univ. of California MercedMalcolm North – USFS Pacific Southwest Research Station Matt Busse – USFS Pacific Southwest Research Station Scott Stephens – Univ. of California Berkeley
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Background• Mixed conifer forest, Central Sierra Nevada, CA• Median historic fire return interval = 6 years, but no fire since 1889• Result: increased tree density, loss of structural heterogeneity, high
fuel loads, risk of uncharacteristically severe wildfire
1929 2008
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Objectives
• Evaluate whether forest treatments designed to restore structural heterogeneity benefits a greater number of ecosystem services.
• Snow capture and melt-out date• Habitat for key old-forest associated wildlife species• Understory biodiversity• Natural regeneration of desired tree species• …while also being resilient to wildfire
• Is restoration of structure and stand resilience best accomplished with thinning, prescribed fire, or a combination?
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Variable Density Thinning study - layout
Stanislaus-Tuolumne Experimental Forest
Thinning treatmentWith prescribed
fireHigh
VariabilityLow
variabilityUntreated
control
Without prescribed fire
High Variability
Low variability
Untreated control
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Logging: Summer 2011 Prescribed burns: Fall 2013
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Snow accumulation & melt data collection(Roger Bales, UC Merced)
• Winters of 2013-2016
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California drought
20002002
20042006
20082010
20122014
2016
44.88
28.9835.2
42.42
28.91
55.9560.82
25.6626.97
43.0540.95
62.78
26.0330.37
25.0228.41
46.23
Ave. since 1922
CA Dept. of Water Resources
Year1940 1950 1960 1970 1980 1990 2000 2010 2020
Snow w
ater content (inches)
0
10
20
30
40
50
60
70Bell Meadow – snow survey
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Snow Depth, DailyMet 2 Array, WY2014-16
Date
Oct-13 Apr-14 Oct-14 Apr-15 Oct-15 Apr-16 Oct-16
Sno
w D
epth
(mm
)
0
200
400
600
800
1000
D70 D72 F65F70F72
Snow Depth, DailyMet 1 Array, WY2014-16
Date
Oct-13 Apr-14 Oct-14 Apr-15 Oct-15 Apr-16 Oct-16
Sno
w D
epth
(mm
)
0
200
400
600
800
1000
V8V9X9X11
Elev. 1735 m
Elev. 1845 m
Snowfall October 2013 – October 2016
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Snow survey – spring 2013At peak accumulation (March 7 survey) the high variability treatment had accumulated, on average, 9 and 3 cm more snow than the control and even thinning treatments, respectively.
By the March 21 survey approximately 86% of the sites had already melted out. The variable treatment retained the most snow followed by the control, then the even units.
M. Pickard thesis – completed Dec. 2015Paper draft in progress
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Vegetation and fuels data collection• Summer 2012 – post logging, pre prescribed burning
• Summer 2014 – first full post-treatment assessment
• Summer 2016 – final field data collection
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Results – tree density
Variable thin with prescribed fire
Diameter class (cm)10-20 20-30 30-45 45-60 60-75 75-90 >90
Trees ac-1
0
100
200
300
400PrePost thinning and burning1929 Reference
Control with prescribed fire
Diameter class (cm)10-20 20-30 30-45 45-60 60-75 75-90 >90
Trees ac-1
0
100
200
300
400PrePost-burning1929 Reference
Prescribed fire: 7% of trees, 2% of basal area killedThin: 77% of trees, 44% of basal area removed
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Results – structural heterogeneityTree density
Sample area (m2)150 225 450
CV
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4 Control High variability thinLow variability thin1929 reference condition
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Results: shrub species richness(3 yrs post-thinning, 1 yr post burn)
©2013 Debra L. Cook
Ceanothus parvifolius
Shrub richness
Treatment
Species per 25m
2
0
1
2
3
4
5
C HV LV C HV LV No Burn Burn
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Summary of early findings• Variable thinning produced within-stand heterogeneity closest to
historical reference condition• Prescribed fire alone did not kill enough trees to substantially
influence heterogeneity• Combined thinning + prescribed burning produced strongest
understory vegetation response• Benefits of variable thinning to physical and ecological response
variables are subtle at this early stage• Slight (non-significant) increase in snow accumulation and snow retention
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Proximity to Rim Fire plus drought/ drought-induced tree mortality has focused attention on the research project• Rim Fire (2013) was the largest in modern history in the Sierra Nevada and
came within 5 miles of the study area• 66+ million trees die from bark beetles – ongoing
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Success best measured by socio-political impactYosemite Stanislaus Solutions - Collaborative of diverse stakeholders from timber industry to environmental groupsJune 26 and July 24, 2015
YSS/TuCARE (Tuolumne County Alliance for Resources and the Environment)
Oct. 6, 2016
• Strong need for action• Forest management very polarized• Variable density thinning – agreement among diverse groups of stakeholders
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Future opportunities• Snow accumulation, melt, soil moisture in high snow-fall winter• Do treatments improve resilience to drought-induced bark beetle
mortality?