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Variable thinning using historical stand structure
data to create fire-resilient forests and enhance
ecosystem services in...
Background
• Mixed conifer forest, Central Sierra Nevada, CA
• Median historic fire return interval = 6 years, but no fire...
Objectives
• Evaluate whether forest treatments designed to
restore structural heterogeneity benefits a greater
number of ...
Variable Density Thinning study - layout
Stanislaus-Tuolumne
Experimental Forest
Thinning treatment
With prescribed
fire
H...
Logging: Summer 2011 Prescribed burns: Fall 2013
Snow accumulation & melt data collection
(Roger Bales, UC Merced)
• Winters of 2013-2016
California drought
44.88
28.98
35.2
42.42
28.91
55.95
60.82
25.6626.97
43.0540.95
62.78
26.03
30.37
25.0228.41
46.23
2000
...
Snow Depth, Daily
Met 2 Array, WY2014-16
Date
Oct-13 Apr-14 Oct-14 Apr-15 Oct-15 Apr-16 Oct-16
SnowDepth(mm)
0
200
400
600...
Snow survey – spring 2013
At peak accumulation (March 7 survey) the high variability
treatment had accumulated, on average...
Vegetation and fuels data collection
• Summer 2012 – post logging, pre prescribed burning
• Summer 2014 – first full post-...
Results – tree density
Variable thin with prescribed fire
Diameter class (cm)
10-20 20-30 30-45 45-60 60-75 75-90 >90
Tree...
Results – structural heterogeneity
Tree density
Sample area (m
2
)
150 225 450
CV
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4 Control
...
Results: shrub species richness
(3 yrs post-thinning, 1 yr post burn)
©2013 Debra L. Cook
Ceanothus parvifolius
Shrub rich...
Summary of early findings
• Variable thinning produced within-stand heterogeneity closest to
historical reference conditio...
Proximity to Rim Fire plus drought/ drought-induced tree
mortality has focused attention on the research project
• Rim Fir...
Success best measured by socio-political impact
Yosemite Stanislaus Solutions - Collaborative of diverse stakeholders
from...
Future opportunities
• Snow accumulation, melt, soil moisture in high snow-fall winter
• Do treatments improve resilience ...
Variable Thinning Using Historical Stand Structure Data to Create Fire-Resilient Forests and Enhance Ecosystem Services in...
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Variable Thinning Using Historical Stand Structure Data to Create Fire-Resilient Forests and Enhance Ecosystem Services in A Changing Climate

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Variable Thinning Using Historical Stand Structure Data to Create Fire-Resilient Forests and Enhance Ecosystem Services in A Changing Climate

  1. 1. Variable thinning using historical stand structure data to create fire-resilient forests and enhance ecosystem services in a changing climate Eric Knapp – USFS Pacific Southwest Research Station Roger Bales – Univ. of California Merced Malcolm North – USFS Pacific Southwest Research Station Matt Busse – USFS Pacific Southwest Research Station Scott Stephens – Univ. of California Berkeley
  2. 2. 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
  3. 3. 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?
  4. 4. Variable Density Thinning study - layout Stanislaus-Tuolumne Experimental Forest Thinning treatment With prescribed fire High Variability Low variability Untreated control Without prescribed fire High Variability Low variability Untreated control
  5. 5. Logging: Summer 2011 Prescribed burns: Fall 2013
  6. 6. Snow accumulation & melt data collection (Roger Bales, UC Merced) • Winters of 2013-2016
  7. 7. California drought 44.88 28.98 35.2 42.42 28.91 55.95 60.82 25.6626.97 43.0540.95 62.78 26.03 30.37 25.0228.41 46.23 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013 2014 2015 2016 Ave. since 1922 CA Dept. of Water Resources Year 1940 1950 1960 1970 1980 1990 2000 2010 2020 Snowwatercontent(inches) 0 10 20 30 40 50 60 70 Bell Meadow – snow survey
  8. 8. Snow Depth, Daily Met 2 Array, WY2014-16 Date Oct-13 Apr-14 Oct-14 Apr-15 Oct-15 Apr-16 Oct-16 SnowDepth(mm) 0 200 400 600 800 1000 D70 D72 F65 F70 F72 Snow Depth, Daily Met 1 Array, WY2014-16 Date Oct-13 Apr-14 Oct-14 Apr-15 Oct-15 Apr-16 Oct-16 SnowDepth(mm) 0 200 400 600 800 1000 V8 V9 X9 X11 Elev. 1735 m Elev. 1845 m Snowfall October 2013 – October 2016
  9. 9. Snow survey – spring 2013 At 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. 2015 Paper draft in progress
  10. 10. 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
  11. 11. Results – tree density Variable thin with prescribed fire Diameter class (cm) 10-20 20-30 30-45 45-60 60-75 75-90 >90 Treesac-1 0 100 200 300 400 Pre Post thinning and burning 1929 Reference Control with prescribed fire Diameter class (cm) 10-20 20-30 30-45 45-60 60-75 75-90 >90 Treesac-1 0 100 200 300 400 Pre Post-burning 1929 Reference Prescribed fire: 7% of trees, 2% of basal area killed Thin: 77% of trees, 44% of basal area removed
  12. 12. Results – structural heterogeneity Tree density Sample area (m 2 ) 150 225 450 CV 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 Control High variability thin Low variability thin 1929 reference condition
  13. 13. Results: shrub species richness (3 yrs post-thinning, 1 yr post burn) ©2013 Debra L. Cook Ceanothus parvifolius Shrub richness Treatment Speciesper25m2 0 1 2 3 4 5 C HV LV C HV LV No Burn Burn
  14. 14. 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
  15. 15. 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
  16. 16. Success best measured by socio-political impact Yosemite Stanislaus Solutions - Collaborative of diverse stakeholders from timber industry to environmental groups June 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
  17. 17. Future opportunities • Snow accumulation, melt, soil moisture in high snow-fall winter • Do treatments improve resilience to drought-induced bark beetle mortality?

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