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1. ?Most current climate?carbon cycle models that include the terrestrial carbon (C) cycle are based on a model developed 40 years ago by Woodwell & Whittaker (1968) and omit advances in biogeochemical understanding since that time. Their model treats net C emissions from ecosystems as the balance between net primary production (NPP) and heterotrophic respiration (HR, i.e. primarily decomposition). 2. ?Under conditions near steady state, geographic patterns of decomposition closely match those of NPP, and net C emissions are adequately described as a simple balance of NPP and HR (the Woodwell-Whittaker model). This close coupling between NPP and HR occurs largely because of tight coupling between C and N (nitrogen)...
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...
Categories: Publication; Types: Citation; Tags: M1-Flora
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...
Categories: Publication; Types: Citation; Tags: M1-Flora
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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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...
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...
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...


map background search result map search result map 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 Climate change and caribou: Effects of summer weather on forage 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 Climate change and caribou: Effects of summer weather on forage