Grass Opal in Some Chestnut and Forested Soils in North Central Oregon

Abstract

Abstract The practicability of using grass opal as an indicator of the vegetative history of soils was investigated in a forest‐grassland transition. Opal phytoliths isolated from grass and other plants were used as standards in the identification of grass opal from soils. Soil horizon samples were selected from 12 locations. Grass opal content was calculated from grain counts of the 15 to 100µ fraction. The content was about 10 times greater in grassland soils than in forest soils. This indicates that the vegetative boundary has been generally stable throughout the time period required for accumulation of the grass opal, estimated to be about 4,000 to 7,000 years. Some change of vegetation was indicated at only two sites. Study of grass opal may be expected to yield much information about the vegetative history of soils.