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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.

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slide1
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

fire history and suppression in sierran mixed conifer forests
Fire History and Suppression in Sierran Mixed-Conifer Forests
  • 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)

Historical Old-Growth

Current High Density Stand

slide3

Forest Regeneration: Species Strategies

P. lambertiana

P. jeffreyi

A. magnifica

A. concolor & C. decurrens

  • 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
slide4

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

study area teakettle experimental forest

California Teakettle Experimental Forest

Fresno

Forest Boundary

Roads

Streams

Structures

Study Area: Teakettle Experimental Forest
  • 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
sampling methodology
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 1st year mortality
pretreatment regeneration pool
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
pretreatment regeneration micro site conditions
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
post treatment mortality and subsequent response white fir
Post-treatment Mortality and Subsequent Response: White fir
  • Initial mortality for A. concolor highest in BS, UC, and US treatments
  • BS and US treatments had the lowest subsequent regeneration response
slide10

Post-treatment Mortality and Subsequent Response: Incense-cedar

1742%

  • All treatments resulted in regeneration decreases
  • Only BS treatments resulted in suppressed regeneration response
slide11

Post-treatment Mortality and Subsequent Response: Jeffrey pine

  • Jeffrey pine regeneration was not present in all treatment combinations
  • 100% Mortality in all treatment combinations
  • Subsequent response only found in BS and US plots
slide12

1500%

Post-treatment Mortality and Subsequent Response: Sugar pine

  • Thinned treatments had regeneration mortality, while un-thinned treatments had 1st
  • year increases in regeneration
  • All treatments had increased regeneration
  • BS and BN treatments had highest 2nd year response
slide13

Axis 2

Post-treatment Regeneration: Micro-site Conditions

  • Increased separation of sugar pine and white fir based on light level
  • and soil moisture
slide14

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 level and increased soil moisture
slide15

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
  • High seed predation of pine seed
  • Seed sowing in predation exclosures allows for a more controlled examination
  • of regeneration with respect to treatments
slide16

Post-treatment: Germinant Survivorship

  • Burned treatments had higher pine germinant survival
  • BC and BS also had the lowest white fir and incense-cedar survivorship
slide17

Species Regeneration Strategies: Conclusions

  • Pre-treatment regeneration dominated by fir and incense-cedar
  • Pre-treatment regeneration distribution and abundance influenced
  • by light level, soil moisture, and litter cover
  • If the goal was to increase pine regeneration and suppress fir and
  • cedar, Burn/Shelterwood was the most effective treatment option
  • Burn treatments favored pine germinant survivorship
  • Study suggests regeneration of pines alone may not be sufficient
  • to accomplish pine restoration
slide18

Species Regeneration Strategies: Conclusions

  • Post-treatment regeneration suggest pine regeneration is
  • occupying lighter and drier sites than white fir and incense-cedar
  • Treatment influence on light level 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

Primary funding provided by the Joint Fire Sciences Program

Additional support provided by The USDA Forest Service PSW Research Station