Testing soil phytolith analysis as a tool to understand vegetation change in the sagebrush steppe and pinyon-juniper woodlands of the Great Basin Desert, USA

Abstract

Better biological proxy methods are needed to understand changes in arid ecosystems over the recent past. Our objective in this study was to examine the utility of soil phytolith analysis to reflect vegetation changes over the past 200 years, from the end of the ‘Little Ice Age’ to present. The sensitivity of phytoliths to record vegetation changes for this time period was tested by sampling in locations where vegetation changes were known to have occurred based on human records. We used extraction weights to test for the trend in reduction of grasses and increase in woody vegetation over time. We used the relative abundance of soil phytolith morphotypes from native versus introduced grasses to look for the increase in non-native grasses. Then, we examined the phytolith assemblages from soils in a continuous core sampling method with 1 cm increments. Extraction weights decreased by half from the surface to ‘Little Ice Age’ layers and may reflect increasing pinyon-juniper woodland cover. The relative abundance of common introduced grass phytoliths increased by nearly half between the older segments and the surface, which could be a reflection of growing dominance of invasive grasses. The phytolith assemblages varied over time and with depth in continuous core sampling. The patterns of change in both detailed cores appeared to reflect known vegetation changes since the end of the ‘Little Ice Age’. Soil phytolith analysis has the potential to provide much needed biological proxy data for this time period in the Great Basin Desert.