Results/Conclusions We found that new tanoak mortality occurred from 2007 to 2009 throughout all sampling strata – redwood and Douglas-fir, “diseased” and “healthy” (as of 2007) – but that the rate of increase, as well as the cumulative impact, was much greater in Douglas-fir forests. In 2007, proportional mortality was higher in the redwood forest type, but by 2009 nearly 100% of tanoak basal area was dead in diseased Douglas-fir plots, as compared to approximately 75% in diseased redwood plots. Our analyses also revealed several indirect effects of this mortality. In redwood forests, tanoak mortality reduced canopy cover, reduced herbaceous cover, increased non-tanoak hardwood regeneration, and increased fuel loading (especially 1000-hour fuels). In Douglas-fir forests, tanoak mortality reduced canopy cover, increased herb species richness, and increased 1-hour and 10-hour fuels. We also detected important baseline differences between these two forest types; Douglas-fir forests exhibited higher tree diversity and greater abundance of non-tanoak hardwoods (i.e. greater functional redundancy), suggesting divergent responses to equivalent levels of tanoak mortality. Finally, we integrate these and other findings to explore potential long-term consequences of this novel disturbance, including interactions with historical disturbances, cascading community-level impacts, and shifts in the composition and structure of affected forests.