| Popis: |
From phytolith and soil data, earlier researchers concluded that Cinnabar Park, a dry grassland surrounded by coniferous forest on a high interfluve (2928 m) in the Medicine Bow Mountains, Wyoming, has migrated downwind (east) by snowdrift action. However, recent soil mapping and studies of soil morphologies and stratigraphy, aided by radiocarbon dating and soil laboratory data, indicate precise alignment of moder soil-vegetation boundaries along the park edge and thus stability of the boundaries. An alternative explanation is that soil formation at the boundaries may be sufficiently rapid so that surface horizons readily reflect slow encroachment of forest onto parkland. In either case, soil characteristics do not support the interpretation that Cinnabar Park is migratory. In the park, ribbon forest, and snowglade (and some forested areas to the west), soil-sediment units give evidence of wind erosion of the interfluve modified by colluviation, resulting in a quartzite-rich, wind-polished stone line (or lines?) about 3 to 10 cm thick that acted as a lag gravel when erosion removed fine particles. The stone line, dated as old as about 2000 yr, is overlain by a surface eolian unit (or locally colluvium) about 5 to 20 cm thick. Soils in the park are developed into the eolian unit, the stone line (or colluvium), and underlying bedrock. We found no evidence that Cinnabar Park was ever forested since the time the stone line formed. Rather, the park is interpreted as a dry park, resulting from soil moisture deficits that prohibit tree expansion. In addition to snow deflation common across the park, moisture deficits are probably caused by poor water penetration from the eolian unit across the stone line into the coarse-textured subsoil. Only where snowdrifts adequately recharge the soil along park margins, or where the eolian unit is thin, can some tree invasion occur, providing that snowdrifting does not fatally damage young seedlings. |
