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Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station

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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Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station

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  1. 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

  2. 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

  3. 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

  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

  5. 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

  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 1st year mortality

  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

  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

  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

  10. Post-treatment Mortality and Subsequent Response: Incense-cedar 1742% • All treatments resulted in regeneration decreases • Immediate post-treatment seedling distribution influenced regeneration response • Only BS treatments resulted in suppressed regeneration response

  11. Post-treatment Mortality and Subsequent Response: Jeffrey pine • 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

  12. 1500% 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 1st • year increases in regeneration • 1st year seedling distribution was the dominant factor influencing regeneration response

  13. Axis 2 Post-treatment Regeneration: Micro-site Conditions • Increased separation of sugar pine and white fir based on light levels • and soil moisture

  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

  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

  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

  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

  18. Species Regeneration Strategies: Conclusions • 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 Primary funding provided by the Joint Fire Sciences Program Additional support provided by The USDA Forest Service PSW Research Station

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