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In 1989, the Chisana caribou (Rangifer tarandus) herd in the northern Wrangell Mountains, Alaska, U.S.A., declined substantially in population size and productivity. Grasses, sedges, forbs, and willows (Salix spp.) are critical components of the diet of caribou in spring and summer, and the abundance and quality of forage are influenced by climate. To evaluate effects of climatic variation on caribou forage we conducted a field experiment in subarctic tundra where light, air temperature, and precipitation were manipulated. We used a plastic tarpaulin to increase air temperature and decrease precipitation. We also decreased light intensity with a shade cloth and increased precipitation by adding water to determine...
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We examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field-based calculations of potential thaw settlement following the loss of remaining ice-rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse-scar features. Up to 0.5 m of thaw settlement was...
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Atmospheric nitrogen (N) fixation by Alnus tenuifolia can account for up to 70% of the N accumulated during vegetation development along river floodplains in interior Alaska. We assessed disease incidence and related mortality of a recent outbreak of fungal stem cankers on A. tenuifolia across three regions in Alaska during the 2005 growing season, and determined the impacts on N-fixation rates, nodule biomass, and stand-level N-fixation inputs. The highest percentage of ramets colonized or dead with canker was found on Tanana River plots, suggesting the epidemic is most severe in the Fairbanks region. A positive relationship between % basal area loss to canker and % canopy loss provides a simple means for assessing...
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Abstract: In this article we extend the theory of community prediction by presenting seven hypotheses for predicting community structure in a directionally changing world. The first three address well-studied community responses to environmental and ecological change: ecological communities are most likely to exhibit threshold changes in structure when perturbations cause large changes in limiting soil or sediment resources, dominant or keystone species, or attributes of disturbance regime that influence community recruitment. Four additional hypotheses address social-ecological interactions and apply to both ecological communities and social-ecological systems. Human responsiveness to short-term and local costs...
We examined the effects of fire disturbance on permafrost degradation and thaw settlement across a series of wildfires (from ~1930 to 2010) in the forested areas of collapse-scar bog complexes in the Tanana Flats lowland of interior Alaska. Field measurements were combined with numerical modeling of soil thermal dynamics to assess the roles of fire severity and climate history in postfire permafrost dynamics. Field-based calculations of potential thaw settlement following the loss of remaining ice-rich permafrost averaged 0.6 m. This subsidence would cause the surface elevations of forests to drop on average 0.1 m below the surface water level of adjacent collapse-scar features. Up to 0.5 m of thaw settlement was...
map background search result map search result map Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests Host species and habitat affect nodulation by specific Frankia genotypes in two species of Alnus in interior Alaska Variation in carbohydrate source–sink relations of forest and treeline white spruce in southern, interior and northern Alaska Disease-Mediated Declines in N-Fixation Inputs by Alnus tenuifolia to Early-Successional Floodplains in Interior and South-Central Alaska Nitrogen additions to pristine, high-latitude, forest ecosystems; consequences for soil nitrogen transformations and retention in mid and late succession Effects of migratory geese on plant communities of an Alaskan salt marsh Nesting Biology of Lesser Canada Geese, Branta canadensis parvipes, along the Tanana River, Alaska Soil and root respiration in mature Alaskan black spruce forests that vary in soil organic matter decomposition rates Twenty-five years of vegetation change along a putative successional chronosequence on the Tanana River, Alaska Vulnerability of white spruce tree growth in interior Alaska in response to climate variability: dendrochronological, demographic, and experimental perspectives Successional and physical controls on the retention of nitrogen in an undisturbed boreal forest ecosystem A first comprehensive census of fungi in soil reveals both hyperdiversity and fine-scale niche partitioning Limitations to Symbiotic Nitrogen Fixation in Primary Succession on the Tanana River Floodplain Climate change and caribou: Effects of summer weather on forage Nitrogen cycling at treeline: Latitudinal and elevational patterns across a boreal landscap Twenty-five years of vegetation change along a putative successional chronosequence on the Tanana River, Alaska Host species and habitat affect nodulation by specific Frankia genotypes in two species of Alnus in interior Alaska Nitrogen additions to pristine, high-latitude, forest ecosystems; consequences for soil nitrogen transformations and retention in mid and late succession Soil and root respiration in mature Alaskan black spruce forests that vary in soil organic matter decomposition rates Successional and physical controls on the retention of nitrogen in an undisturbed boreal forest ecosystem Limitations to Symbiotic Nitrogen Fixation in Primary Succession on the Tanana River Floodplain Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests A first comprehensive census of fungi in soil reveals both hyperdiversity and fine-scale niche partitioning Effects of migratory geese on plant communities of an Alaskan salt marsh Nesting Biology of Lesser Canada Geese, Branta canadensis parvipes, along the Tanana River, Alaska Climate change and caribou: Effects of summer weather on forage Variation in carbohydrate source–sink relations of forest and treeline white spruce in southern, interior and northern Alaska Disease-Mediated Declines in N-Fixation Inputs by Alnus tenuifolia to Early-Successional Floodplains in Interior and South-Central Alaska Vulnerability of white spruce tree growth in interior Alaska in response to climate variability: dendrochronological, demographic, and experimental perspectives Nitrogen cycling at treeline: Latitudinal and elevational patterns across a boreal landscap