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Aim: A conspicuous climatic and biogeographical transition occurs at 40?45� N in western North America. This pivot point marks a north?south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat-midden record northward into the lowlands of the central Rocky Mountains. Published...
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Rapid expansion of cropland threatens grassland ecosystems across western North America and broad-scaleplanning can be a catalyst motivating individuals and agencies to accelerate conservation. Sprague’s Pipit(Anthus spragueii) is an imperiled grassland songbird whose population has been declining rapidly in recent decades.Here, we present a strategic framework for conservation of pipits and their habitat in the northern GreatPlains.We modeled pipit distribution across its million-km2 breeding range in Canada and the U.S.We describefactors shaping distribution, delineate population cores and assess vulnerability to future grassland losses. Pipitsselected landscapes with a high proportion of continuous grassland...
We present new 3He surface exposure ages on moraines and bedrock near the summit of Mauna Kea, Hawaii, which refine the age of the Mauna Kea Ice Cap during the Local Last Glacial Maximum (LLGM) and identify a subsequent fluctuation of the ice margin. The 3He ages, when combined with those reported previously, indicate that the local ice-cap margin began to retreat from its LLGM extent at 20.5 ± 2.5 ka, in agreement with the age of deglaciation determined from LLGM moraines elsewhere in the tropics. The ice-cap margin receded to a position at least 3 km upslope for ∼ 4.5–5.0 kyr before readvancing nearly to its LLGM extent. The timing of this readvance at ∼ 15.4 ka corresponds to a large reduction of the Atlantic...
Categories: Publication; Types: Citation; Tags: geochronology, glacial, palioclimate
Hydromechanical effects of continental ice sheets may involve considerably more than the widely recognized direct compression of overridden terrains by ice load. Lithospheric flexure, which lags ice advance and retreat, appears capable of causing comparable or greater stress changes. Together, direct and flexural loading may increase fluid pressures by tens of MPa in geologic units unable to drain. If so, fluid pressures in low-permeability formations subject to glaciation may have increased and decreased repeatedly during cycles of Pleistocene glaciation and can again in the future. Being asynchronous and normally oriented, direct and flexural loading presumably cause normal and shear stresses to evolve in a complex...
Aim: A conspicuous climatic and biogeographical transition occurs at 40–45° N in western North America. This pivot point marks a north–south opposition of wet and dry conditions at interannual and decadal time-scales, as well as the northern and southern limits of many dominant western plant species. Palaeoecologists have yet to focus on past climatic and biotic shifts along this transition, in part because it requires comparisons across dissimilar records [i.e. pollen from lacustrine sediments to the north and plant macrofossils from woodrat (Neotoma) middens to the south]. To overcome these limitations, we are extending the woodrat-midden record northward into the lowlands of the central Rocky Mountains.
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Temperate grassland ecosystems are imperiled globally, and habitat loss in North America has resulted in steepdeclines of endemic songbirds. Commercial livestock grazing is the primary land use in rangelands that supportremaining bird populations. Some conservationists suggest using livestock as “ecosystem engineers” to increasehabitat heterogeneity in rangelands because birds require a spectrum of sparse to dense vegetation cover.However, grazing effects remain poorly understood because local studies have not incorporated broad-scaleenvironmental constraints on herbaceous growth. We surveyed grassland birds across a region spanning26 500 km2 in northeast Montana, United States to assess how distribution and abundance...
    map background search result map search result map Precipitation and Soil Productivity Explain Effects of Grazing on Grassland Songbirds One step ahead of the plow: Using cropland conversion risk to guide Sprague's Pipit conservation in the northern Great Plains Precipitation and Soil Productivity Explain Effects of Grazing on Grassland Songbirds One step ahead of the plow: Using cropland conversion risk to guide Sprague's Pipit conservation in the northern Great Plains