Phytoliths as Tracers of Recent Environmental Change

Abstract

Phytoliths are more widespread, accessible, and characteristic of a local area than other terrestrial vegetation proxies. Despite work on recent soil and Cenozoic paleosol phytolith assemblages, environmental applications lag significantly behind their potential in terms of temporal resolution. Modern soil phytolith assemblages, aboveground vegetation, and soil features from Inceptisols with known vegetation and environmental histories were sampled in order to develop methods for describing rapid environmental change events at a high temporal resolution. Samples included agricultural fields, fluvial meanders, and wildfire sites. In each case, soil phytolith assemblages were unrepresentative of current vegetation but were characteristic of the known environmental history. As a result, rapid changes in land use or environment are identifiable in phytolith assemblages; agricultural sites can be identified by Ap horizons and grass phytoliths, fluvial meanders by weakly developed soils with channel features and spatial phytolith gradients, and wildfire sites by charcoal bodies and bimodal phytolith assemblages. These sites also provide rates of change, specific to each type of environmental change. An ecosystem experiencing wildfires changes assemblages rapidly (1–2 % per year), while change resulting from channel migration occurs slightly slower (~ 0.5 % per year), and that from field abandonment occurs significantly slower (< 0.25 % per year). These methods can be applied to paleovegetation reconstructions, providing additional environmental information and higher-resolution vegetation interpretations. Along with more work on spatial and depth-profile sampling, these results will allow high temporal resolution for environmental and vegetation change records both in the modern and throughout the Cenozoic era.