Silvicultural and Reserve Impacts on Potential
Fire Behavior and Effects: Sierra Nevada
Mixed Conifer Forests
Scott Stephens1 and Jason Moghaddas2
1Department of Environmental Science,
Policy, and Management, UC Berkeley
2Mt. Hough Ranger District, Plumas
National Forest
Sierra Nevada Mixed Conifer Forests
• Past management activities have modified forest
structure
– Harvesting, fire suppression, livestock grazing
• Many forests currently have very high fire
hazards
• How do traditional silvicultural systems and
reserves effect potential fire behavior and
effects?
Study Location
Blodgett Experimental Forest, UC Berkeley
North-central Sierra Nevada
Mixed conifer forests
Elevation 3800-4600 feet
Surface fire once common at Blodgett
Composite fire return intervals 6-14 years
at 7-12 acre spatial scale (range 4-28 yrs)
Fires rare after 1910
Stephens and Collins 2004
Blodgett Management History
1849-1900: Grazing, logging by oxen in the
1890’s
1900-1913: Extensive railroad logging over
most of forest (seed tree method)
UC in 1933
1960-1970: Removal of most residual old
trees
1849-1970: Common in Sierra Nevada
Sierra Nevada Traditional
Silvicultural Systems and Reserves
• Primary management goals have not been
fire performance until about 10 years ago
• Traditional silvicultural systems primarily
used to balance growth and yield of wood
products while protecting soil and
biological resources
• Reserves are primarily areas managed
under fire suppression, other inputs rare
Systems Examined
•
•
•
•
•
Individual tree selection
Thin from below
Over story removal
Plantations less than 5 year old
Plantations 15-19 years old that were
untreated, masticated at 11-13 years with
spot herbicide, or hand thinned once at
11-13 years with spot herbicide
Individual Tree Selection
Thin From Below
Over Story Removal
Plantation Less Than 5 Years Old
Plantation 15-19 Years,
No Treatment
Plantation 15-19 Years, Masticated
Plantation 15-19 Years, Thinned
Systems continued
• Young-growth reserve. After seed tree
harvest in early 1900’s no other treatments
except fire suppression
• Old-growth reserves. Reserve stands with
significant component of old-growth trees.
• All silvicultural systems and reserves had
3 replicates (each replicate 40-60 acres)
• Plantation site prep, leave duff-litter and
some surface fuels for erosion control.
Others: lop and scatter of activity fuels
Old-Growth Reserve
Young Growth Reserve
Vegetation and Potential Fire Effects
• Tree inventory in systematic grid of plots
(species, dbh, height, height to live crown)
• Complete surface and ground fuel inventory
(Brown transects, van Wagtendonk’s data)
• Determine susceptibility to crown fire (passive
and active) and potential tree mortality for all
treatments
• Use Fuels Management Analyst (FMA Plus).
Good model for stand scale (Don Carlton
developed).
FMA Plus
• Integrates many standard models such as:
• Rothermel surface fire model (1972)
• Alexander (1988) and van Wagner (1993)
crown fire models
• Scott and Reinhardt (2001) torching and
crowning indices
• Reinhardt et al. (1991) mortality models
Results
• 27 experimental units had 3534 live trees
before treatments (9 treatments, 3 reps)
• 436 fuel transects used to estimate
surface and ground fuels
• Allometric equations used to estimate
crown and ladder fuels using FMA Plus
• Fire Family Plus used to develop 80th, 90th,
and 97.5th percentile weather (30 years)
Fire Performance
• Old-growth reserve, young-growth
reserve, and thin from below produced the
best fire performance (97.5th percentile)
– Torching index 41, 55, 39 miles/hr
– Crowning index 19, 21, 23 miles/hr
– All 100% surface fire
• Tall overstory trees and high HLCB important
• ITS, over story removal, plantations, all
had lower torching index, mix of active and
passive crown fires
Fire Performance: Mortality
• Old-growth reserve, young-growth
reserve, and thin from below produced the
best fire performance (97.5th percentile)
– Trees 10-20 in DBH: 63%, 57%, 58%
– Trees 20-30 in DBH: 10%, 8%, 10%
– Trees > 30 in DBH: 4%, 3%, 3%
• ITS, over story removal, plantations, all
had much higher mortality (30-100%)
• Stephens and Moghaddas 2005
Forests in Northwestern Mexico
Sierra San Pedro Martir (SSPM)
Within the California floristic province
– unique to Northern Baja California
Forested area approximately 40,000 ha
Elevation upper plateau 2600 m
– 3 large plateaus
Jeffrey pine-mixed conifer forests
– Similar to forests in southern California and
eastern Sierra
Fire suppression begins in 1970, no harvesting
Image 1: Aerial
Wildfire July 4, 2003
• Started in chaparral below forest
– In SSPM lightning ignited fires
suppressed by 8 person hand crew
• Very low hazards, suppression efficient
• Fire burned approximately 4000 ha
• Largest fire in 20 years
– Occurred during drought period
Wildfire Impacts
• Approximately 5% of dominant and codominant trees killed (study in progress)
• Fire was very patchy
– directly linked to heterogeneity of
forest structure and fuels
• Stephens 2004; Stephens and Gill 2005
• produces fire with diverse effects
• continues high spatial heterogeneity
• bark beetles killing a few trees
• Wildfire at end of 5 year drought
Summary
Old-growth and young-growth reserves,
thin from below: best fire performance
Reserves with similar forest structure and
topography could possibly be managed
with Wildland Fire Use
Thin from below removed ladder fuels
Most silvicultural systems did not produce
structures resistant to wildfire effects
Not too surprising since not a key objective
Summary
• Need new set of silvicultural prescriptions to
meet fire performance criteria (FFS)
• High variability in initial forest structure and
topography necessitates ground-based
solutions (SSPM structure)
• Adaptive management is key to facilitate
learning, participation, and to update
prescriptions
Stephens and Ruth 2005
Acknowledgements
Bob Heald and Frieder Schurr, UC Center for Forestry
Blodgett Foresters and Summer Technicians
John Battles and Carrie Salazar, UC Berkeley, for
finishing the BFRS on-line database
Funding: Resources Legacy Fund
Published papers available at
http://www.cnr.berkeley.edu/stephens-lab/people.htm
Hit the ‘Testimonies and Publication’ link by Scott’s
picture