UC Irvine

While 80% of plant species are associated with mycorrhizal fungi, the impacts of ecological restoration on mycorrhizal fungi are rarely explored in scientific literature. Ecological restoration is an interdisciplinary endeavor, requiring partnerships with a diverse array of stakeholders. Increasing partnerships with restoration practitioners and mycologists will fill important knowledge gaps in our understanding of restoration efforts. Since mycorrhizal fungi provide a myriad of services to plant hosts, the efficacy of restoration efforts can improve with such partnerships. For my first chapter, I collaborated with the Newport Bay Conservancy to explore the effects of invasive species removal on mycorrhizal fungi. For my second and third chapters, I partnered with Save the Redwoods League to examine the response of mycorrhizal fungi to restorative thinning and road removal. Taken together, my dissertation chapters provide evidence that fungal communities play an important role in the success of restoration efforts and can inform management decisions.

In Chapter 1, I assessed the effect of full and selective removal of the invasive Brazilian pepper tree (Schinus terebinthifolius) on mycorrhizal fungi. To provide a trajectory for the restoration of the mycorrhizal community, I examined the effect of selective removal on the native Arroyo willow (Salix lasiolepis). An important distinction between the selective and full removal was that the full approach deployed a soil amendment. The results showed a disparity between full and selective removal, where the diversity of ectomycorrhizal fungi (EMF) declined significantly after selective removal. However, full removal led to a significant increase in the diversity of EMF. The results of our study point to the soil amendment as a significant factor that led to the increase of EMF.

For Chapter 2, I assessed the effects of logging and restorative thinning in second-growth redwood (Sequoia sempervirens) forests. Mycorrhizal fungi are important in these ecosystems, where redwoods use arbuscular mycorrhizal fungi (AMF) and EMF. However, following timber harvests, pine trees (Pinaceae) were aerially seeded. Since pine trees use EMF exclusively, the encroachment of pine woodland can restrict the use AMF by redwood forests. Our predictions were supported with the significantly lower abundance and diversity of AMF in second-growth forests. This trend was found in soils and a specialized root structure for AMF known as the rhizonode. When pine trees were removed, we expected the presence of AMF would change. However, the presence of AMF was still lower compared to old-growth. The results of our study provide a new trajectory for the restoration of second-growth forests, where restoration efforts should aim to establish a mycorrhizal community indicative of old-growth.

Chapter 3 explored the effect of road removal on mycorrhizal fungi and the broader fungal community. In this chapter, I continued the examination of restoration efforts in second-growth redwood forests. Since 2004, road removal has been an integral part of ecosystem restoration. I expected road removal efforts would lessen the diversity and abundance of mycorrhizal fungi. However, we found a recent road removal led to an increase in the abundance of EMF. In accordance with our predictions, pathogenic fungi that are detrimental to redwood health were lowest in old-growth forests and the oldest removal site. Moreover, saprotrophic fungi involved in decomposition were lowest in the road-center compared to the roadside. The results of this study show that restoration efforts should focus on restoring saprotrophic fungi in the road-center, which facilitate nutrient cycling and the recovery of redwood forests.