Climate Change, Wildfire, and Biotic Drivers of Oak Woodland Health

Richard C Cobb, Department of Natural Resources & Environmental Science, California Polytechnic State University, San Luis Obispo

Most of California’s population resides within or adjacent to the state’s oak woodlands. Thus, the health and economic stability of the state is coupled with these ecosystems, despite what is also often a relatively low timber value. Oak woodlands are threatened by numerous pathogens and insects, but the interactions with these biotic organisms and climate change and/or wildfire holds potential for far greater threats to their ecological function. Pathogens and insects of the canopy, cambium, and root systems of oak forests each has distinct manners in which they may be suppressed or magnified by wildfire and/or climate change. At the same time, oak pathogens and insects may suppress or magnify wildfire impacts or risk. I present a unified framework for approaching these interactions with management, policy, or research goals. While state and federal policy is critical to addressing wildfire, most land managers work at the stand level and must treat climate change as an overarching problem where solutions are multi-generational. In contrast, mitigating vegetation conditions conducive to biological tree mortality or directly suppressing harmful insects and pathogens are conducted at the stand level. This creates potential to combine approaches and make progress on multiple management goals. While many classes of insect and pathogen attack help elucidate tradeoffs between treating vegetation vs biological agents, I demonstrate these tradeoffs with a series of research and management case studies focused on Phytophthora ramorum, cause of sudden oak death and the most consequential pathogen to oak forests in the state.