Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW...
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Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR 97331 Tree Regeneration Strategies in Response to Burning and Thinning Restoration Treatments in a Sierran Mixed-Conifer Forest
Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR 97331 Tree Regeneration
Harold S.J. Zald and Andrew N. Gray USDA Forest Service,
Pacific Northwest Research Station 3200 SW Jefferson Way,
Corvallis, OR 97331 Tree Regeneration Strategies in Response to
Burning and Thinning Restoration Treatments in a Sierran
Mixed-Conifer Forest
Slide 2
Historic fire return interval 12-17 years Fire suppression has
been a dominant management strategy in Sierran mixed- conifer
forests on public lands Generalized impacts of fire suppression
Increased stand densities Increased ladder fuels and fuel loadings
Reduced fire frequency Increased fire severity Increased dominance
of fire intolerant and shade tolerant species (firs and
incense-cedar) Fire History and Suppression in Sierran
Mixed-Conifer Forests Historical Old-GrowthCurrent High Density
Stand
Slide 3
Regeneration dynamics a major driver of future composition,
structure and function Seeding germination and establishment is a
highly sensitive life history stage Restoration treatments may
impact future regeneration patterns Forest Regeneration: Species
Strategies P. jeffreyi P. lambertiana A. concolor & C.
decurrens A. magnifica
Slide 4
Study Objectives Past:Pretreatment regeneration composition and
abundance Pretreatment regeneration with respect to environmental
conditions Pretreatment environmental conditions Present:Treatment
mortality and subsequent response Germinant success in relation to
treatments Post-treatment regeneration with respect to
environmental conditions Future:Treatment effects on environmental
conditions
Slide 5
Study Area: Teakettle Experimental Forest Fresno California
Teakettle Experimental Forest Forest Boundary Roads Streams
Structures Full factorial design contrasting two levels of burning
and three levels of thinning treatments Burn treatments: no burn
(U), and understory burn (B) Thinning treatments: no thinning (N),
CASPO understory thinning (C), and overstory shelterwood thinning
(S) Each treatment unit is a 4 ha plot with three replicates, for a
total of 18 plots
Slide 6
Sampling Methodology Regeneration and Micro-site Conditions All
trees less than 5cm DBH tallied on 402 systematically placed 3.5m
radius plots Solar radiation estimated by hemispherical photography
Volumetric soil moisture estimated using time domain reflectometry
(TDR) Vegetation and substrate cover tallied Germination and
Survivorship Predation exclosures (18 per treatment combination)
Seeded with dominant overstory species in the first post-treatment
year (Oct 2002) Germinants closely monitored during summer 2003 to
record total germinants and 1 st year mortality
Slide 7
Pretreatment: Regeneration Pool A. concolor and C. decurrens
are the most common overstory trees, P. jeffreyi and P. lambertiana
are major overstory components Regeneration pool dominated by firs
and incense-cedar, with a reduced pine component
Slide 8
Pretreatment Regeneration: Micro-site Conditions A.
magnifica(ABMA) low DSF, moderate soil moisture, high litter cover
C. decurrens(CADE) low DSF, high soil moisture A. concolor (ABCO)
intermediate DSF and soil moisture P. lambertiana (PILA)
intermediate DSF and soil moisture P. jeffreyi (PIJE) high DSF, low
soil moisture
Slide 9
Post-treatment Mortality and Subsequent Response: White fir
Initial mortality for A. concolor highest in BS, UC, and US
treatments US, UC, BS, and UN (control) treatments had the lowest
subsequent regeneration response
Slide 10
All treatments resulted in regeneration decreases Immediate
post-treatment seedling distribution influenced regeneration
response Only BS treatments resulted in suppressed regeneration
response Post-treatment Mortality and Subsequent Response:
Incense-cedar 1742%
Slide 11
Jeffrey pine regeneration was not present in all treatment
combinations Burning, thinning, and burn/thinning combinations
influenced mortality Subsequent response only found in BS and US
plots Unbalanced distribution prevented response model development
Post-treatment Mortality and Subsequent Response: Jeffrey pine
Slide 12
Post-treatment Mortality and Subsequent Response: Sugar pine
Pretreatment regeneration distribution, thinning, and burn/thinning
combinations affected regeneration mortality Thinned treatments had
regeneration mortality, while un-thinned treatments had 1 st year
increases in regeneration 1 st year seedling distribution was the
dominant factor influencing regeneration response 1500%
Slide 13
Axis 2 Post-treatment Regeneration: Micro-site Conditions
Increased separation of sugar pine and white fir based on light
levels and soil moisture
Slide 14
Post-treatment: Micro-site Conditions Thinning treatments have
dominant effect on light levels and soil moisture Burning
treatments have a lesser but consistent influence Increased light
levels and increased soil moisture
Slide 15
Post-treatment: Germination Study Natural regeneration surveys
do not address seed source Firs and incense-cedar are prolific seed
producers compared to pines High proportion of firs and
incense-cedar in the overstory indicates regeneration surveys may
have a seed input bias Pines seeds also tend to have high seed
predation Seed sowing in predation exclosures allows for a more
controlled examination of regeneration with respect to
treatments
Slide 16
Post-treatment: Germinant Survivorship Burned treatments had
higher pine germinant survival BC and BS also had the lowest white
fir and incense-cedar survivorship
Slide 17
Species Regeneration Strategies: Conclusions Pre-treatment
regeneration dominated by fir and incense-cedar Pre-treatment
regeneration distribution and abundance influenced by light levels,
soil moisture, and litter cover If the goal is to increase pine
regeneration and suppress fir and cedar, Burn/Shelterwood was the
most effective treatment option Burn treatments favored pine
germinant survivorship High germinant study response of pines
combined with low natural regeneration of pines suggests natural
regeneration may not be sufficient to accomplish pine
restoration
Slide 18
Post-treatment regeneration suggest pines are occupying lighter
and drier sites than white fir and incense-cedar Treatment
influence on light levels and soil moisture may benefit future pine
regeneration when light levels increase with little increase in
soil moisture Management goals for specific species or structural
conditions may not be compatible with restoration activities whose
objectives are increased pine components Species Regeneration
Strategies: Conclusions Primary funding provided by the Joint Fire
Sciences Program Additional support provided by The USDA Forest
Service PSW Research Station