OPAL PHYTOLITHS AS AN INDICATOR OF THE FLORISTICS OF PREHISTORIC GRASSLANDS

A strong relationship between current vegetation and the opal phytolit h content of surface soil was established. Opal phytoliths obtained fr om buried soil surface horizons 200-800 years old were then used to es tablish a profile of the vegetation present on four sites within Capit ol Reef National Park, Utah, USA, prior to European settlement. The pl ant communities so reconstructed contained more forbs and/or shrubs th an present-day communities and were dominated by cool-season rather th an warm-season grasses. Although these differences could be due to cli mate change, the pattern of change from cool-season to warm-season gra sses is not consistent with the accepted pattern of climate change. Gr azing pressure could account for this change in plant community compos ition. Livestock tend to graze Capitol Reef in the cool season, and th e area is rested from grazing during the warm season. This pattern cou ld account for the decline in cool-season grasses. Phytolith analyses can serve as an alternative method for assessing the impact of managem ent on grasslands. This method is particularly valuable when no compar able ''undisturbed'' control area exists.