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. 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. 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. 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. Logging: Summer 2011 Prescribed burns: Fall 2013

7. Snow accumulation & melt data collection
(Roger Bales, UC Merced)
• Winters of 2013-2016

8. 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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Future opportunities
• Snow accumulation, melt, soil moisture in high snow-fall winter
• Do treatments improve resilience to drought-induced bark beetle
mortality?