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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.

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Presentation on theme: "Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR 97331 Tree Regeneration."— Presentation transcript:

1 Harold S.J. Zald and Andrew N. Gray USDA Forest Service, Pacific Northwest Research Station 3200 SW Jefferson Way, Corvallis, OR Tree Regeneration Strategies in Response to Burning and Thinning Restoration Treatments in a Sierran Mixed-Conifer Forest

2 Historic fire return interval 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

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

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 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

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

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 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%

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

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%

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 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


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