Inoculant-Supported Restoration of Oaks (Quercus spp.) along Riparian Areas in the San Francisco Bay Area

Isaiah Thalmayer, Point Blue Conservation Science

Chelsea J. Carey, Point Blue Conservation Science

Kristen Dybala, Point Blue Conservation Science

Thomas Gardali, Point Blue Conservation Science

Over the past century, up to 98% of riparian habitat in California has been lost or degraded, making restoration critically important. Oaks constitute an important part of natural and restored plant communities along riparian areas, but unlike many of the other co-occurring woody species, oaks form relationships with a particular kind of mycorrhizal fungi (ectomycorrhizal fungi or EMF) that may be absent or nearly absent from degraded sites. Mycorrhizal fungi confer many benefits to plants, and the absence of EMF may reduce establishment and vigor, and increase mortality, of oak species as the climate warms and droughts become more extreme and frequent. In the fall of 2019, we established a field experiment to assess the effects of EMF inoculation on the establishment and near-term success of Quercus agrifolia and Quercus lobata individuals across three sites in Marin and Sonoma Counties. We compared two different inoculum sources to a control: whole-soil inoculum sourced from beneath mature Q. agrifolia and Q. lobata trees in 1) reference riparian areas currently experiencing a similar climate to the restoration sites and 2) reference riparian areas currently experiencing warmer and drier conditions compared to the restoration sites (n = 8 per treatment per site). We hypothesized that seedlings supplied with inoculum adapted to warm and dry conditions would show increased establishment in the face of near-term stressors and would withstand future climate conditions better in the long-term. In this talk, we will present first year results of the experiment, focusing on germination rates, growth, and vigor of oak seedlings as affected by treatment.