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Assessing post-wildfire conifer regeneration: Validation of a non-destructive seedling aging method

Author(s): Eva K. Strand, Darcy H. Hammond
Year Published: 2020

Determining the age of natural conifer regeneration following wildfires is crucial to understanding ecological trajectories and predicting post-fire effects in conifer forests. However, traditional methods of determining seedling age via growth ring counts requires killing desirable seedlings, while the validity of non-destructive alternatives is undetermined in many species. In 2016 and 2017 we sampled ponderosa pine (Pinus ponderosa) in central Oregon (dry ponderosa) and southeast Washington (dry mixed conifer), grand fir (Abies grandis) in southeast Washington, and black spruce (Picea mariana) in Interior Alaska (boreal spruce). Seedlings were sampled within wildfires that had burned in either 2004 (Alaska), 2005 (Washington), or 2007 (Oregon) as well as from unburned areas within or immediately outside the fire perimeter. Seedling age was estimated in the field by counting terminal bud scars, after which seedlings were cut at ground level. The “true” age was then determined by counting basal growth rings using WinDENDRO software. The precise accuracy(where bud scar age was equal to ring count age)was 17% for ponderosa, 18% for grand fir, and 27% for black spruce, which increased to 49%, 45%, and 56% accuracy at +/-one year accuracy. Bud scar counts underestimated age by an average of 1.8 years for ponderosa, 1.6 for grand fir, and 0.84 for black spruce. For all species our results show that accuracy was best for seedlings younger than ~15 years, likely due to bark formation in older seedlings that covers early bud scars, and on non-suppressed seedlings, i.e. seedlings that were relatively tall fora given age. In general, our findings agree with those of previous studies on non-destructive aging methods, that these non-destructive methods can be accurate enough for some applications but are likely inappropriate for applications requiring high precision of seedling aging.

Citation: Strand EK and Hammond DH. 2020. Assessing post-wildfire conifer regeneration: Validation of a non-destructive seedling aging method. Final Report to the Joint Fire Science Program for Contract 17-2-01-11, 22p.
Topic(s): Recovery after fire, Resilience
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 22237
Record updated: Dec 7, 2020