Oak Woodland Regeneration and the 2017 Tubbs Fire

Michelle Halbur, Sasha Berleman, Michael Gillogly, Devyn Friedfel, and Tosha Comendant

Published May 2019 in International Oaks No. 30: 153–160

Abstract

Multiple oak species in California have evolved to withstand fire disturbance through association with a Mediterranean climate and Native American peoples. Future climate models forecast increased fire frequency in the North Coast region of California (Krawchuk and Morritz 2012). Combined with fire suppression and increasing fuel loads and fire severity, the resiliency of coastal oak forests to future wildfires is not well understood. In October 2017, the Tubbs Fire burned through Pepperwood Preserve. Prior to this disturbance, multiple sites were undergoing treatment for Pseudotsuga menziesii var. menziesii (Douglas-fir) encroachment including seven hectares of Quercus kelloggii (black oak), Q. agrifolia var. agrifolia (coast live oak), and mixed oak forest. These areas had been thinned from below and prescribed burns were planned. In management areas, modified plots of Brown’s (1974) transects were used to sample approximately 10% of the management area for pre- and post-fire effects on the herbaceous understory community, tree canopy cover, seedling recruitment, and fuels. After the 2017 Tubbs Fire, about 66% of all trees (n=100) exhibited full canopy leaf scorch and another 13% (n=20) had no leaves due to full canopy consumption. We also detected a statistically significant decrease in fuels and the number of tree seedlings. Given an 80% reduction in the litter/duff layer, future oak seedling recruitment may be enhanced by the direct contact of acorns with the soil. During 2018 surveys we documented mortality, regeneration, and recruitment in all fuel treatment plots. Through long-term monitoring of fuel treatment efforts and interactions with wildfire in this region, we will increase knowledge of factors impacting oak-forest resiliency.

Keywords

Tubbs Fire, fire management, oak woodlands, fire suppression

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