Publication Date

Fall 2023

Degree Type


Degree Name

Master of Science (MS)


Environmental Studies


Rachel O'Malley; Will Russell; Katerina Estera-Molina


Woody species encroachment depletes historic grassland biodiversity and degrades ecosystem function around the world. In particular, the encroaching trees can shift soil properties and microbial communities, which play critical roles in plant health and global nutrient cycling. Little is known about how removing encroached trees affects soil ecosystems, however. Over the last century, Pinus radiata and Hesperocyparis macrocarpa (non-native to the area) both encroached into coastal prairies at Rancho Corral de Tierra in California, and selected trees were removed in 2017 and 2018 to restore grassland habitats. To examine the impacts of encroachment and removal on the soil ecosystem, I compared the soil microbial community alpha diversity, composition, relative abundance, and soil characteristics across three vegetation types: uninvaded grassland, conifer-encroached areas, and areas where trees were removed four to five years previously. I found that tree encroachment had reduced both bacterial and fungal community alpha diversity by up to 102% and increased soil moisture, C:N ratios, and total carbon. Post-removal soil bacterial communities were more similar to those in grasslands than tree-encroached areas, but fungal communities remained more similar to encroached area fungal microbiomes. Removal may be a good initial step to partially reverse impacts of trees, but long-term monitoring and adaptive management is needed to ensure soil microbial communities are restored to fully functioning grassland microbiomes.