Phytoliths as indicators of plant community change: A case study of the reconstruction of the historical extent of the oak savanna in the Willamette Valley Oregon, USA

•Phytolith analysis was used to establish historical vegetation.•Spatial distribution of historic vegetation indicated tree encroachment.•Phytolith analysis can be used to set goals for ecological restoration efforts.

The Oregon white oak savanna, once common in Oregon's Willamette Valley, has been reduced to less than 1% of its former extent. For ecological restoration purposes, we used phytolith analysis to establish both historical vegetation composition and structure at the Jim's Creek research site in Oregon, USA. We sampled the soil at 47 selected plots, extracted the phytoliths, and determined the composition of the phytolith assemblages. Based on the ratios of grass and tree phytoliths in the samples, each site was assigned to one of three ecotopes that, through phytoliths, describe the historic vegetation mosaic. By reconstructing the spatial distribution of historic vegetation types, we were able to confirm the pattern of conifer encroachment on former savanna as suggested by other studies.