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Clastic and organic sediments exposed in two stream cutbanks above modern timberline in the headwaters of the Henrys Fork drainage record multiple episodes of fluvial, lacustrine and wetland deposition. The location of the upper Henrys Fork at the boundary between modern summer-wet/winter-dry and summer dry/winter-wet precipitation regimes suggests that changes in vegetation during the Holocene were due primarily to variations in growing-season temperature. A radiocarbon date of 9310 6 70 BP on a Salix fragment from the base of one exposure indicates that the upper reaches of the Henrys Fork were vegetated by riparian willows by the early Holocene. Four other dates on wood and bulk organics ranging up to 4070 6...
Because of the difficulties involved with separating natural fluctuations in climatic variables from possible directional changes related to human activities (e.g., heightened atmospheric CO2 concentrations related to fossil fuel consumption), some researchers have focused on developing alternative indicators to detect hypothesized climate changes. It has, for example, been suggested that the locations of ecotones, transitions between adjacent ecosystems or biomes, should be monitored. It is assumed that changes in climate, especially increases in atmospheric temperature, will result in shifts in the location (altitude or latitude) of ecotones as plants respond to the newly imposed climatic conditions. In this article,...