Skip to main content
Advanced Search

Filters: Contacts: Kielland, Knut (X)

131 results (39ms)   

View Results as: JSON ATOM CSV
thumbnail
The fundamental niche of a species is rarely if ever realized because the presence of other species restricts it to a narrower range of ecological conditions. The effects of this narrower range of conditions define how resources are partitioned. Resource partitioning has been inferred but not demonstrated previously for sympatric ursids. We estimated assimilated diet in relation to body condition (body fat and lean and total body mass) and reproduction for sympatric brown bears (Ursus arctos) and American black bears (U. americanus) in south-central Alaska, 1998?2000. Based on isotopic analysis of blood and keratin in claws, salmon (Oncorhynchus spp.) predominated in brown bear diets (>53% annually) whereas black...
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)...
thumbnail
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...
Black spruce (Picea mariana) forests represent the dominant vegetation type throughout the North American and Siberian taiga and are generally considered to be pristine, N-limiting environments. The aim of this study was to investigate the fundamental underlying mechanisms which control N availability in these soils with particular reference to the dynamics of dissolved organic nitrogen (DON). Our results showed that in these highly organic and low pH soils, soluble N is dominated by organic forms with correspondingly low concentrations of ammonium and nitrate. Amino acids, which are known to be directly taken up by plants growing in these soils, were calculated to constitute 10–20% of the total DON pool. The microbial...
Black spruce (Picea mariana) forests represent the dominant vegetation type throughout the North American and Siberian taiga and are generally considered to be pristine, N-limiting environments. The aim of this study was to investigate the fundamental underlying mechanisms which control N availability in these soils with particular reference to the dynamics of dissolved organic nitrogen (DON). Our results showed that in these highly organic and low pH soils, soluble N is dominated by organic forms with correspondingly low concentrations of ammonium and nitrate. Amino acids, which are known to be directly taken up by plants growing in these soils, were calculated to constitute 10–20% of the total DON pool. The microbial...
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 Nitrogen retention in the hyporheic zone of a glacial river in interior Alaska Understanding the effects of wildfire severity on moose habitat characteristics and use in Interior, Alaska INTERSPECIFIC RESOURCE PARTITIONING IN SYMPATRIC URSIDS Nitrogen retention in the hyporheic zone of a glacial river in interior Alaska Understanding the effects of wildfire severity on moose habitat characteristics and use in Interior, Alaska Interactive effects of wildfire and climate on permafrost degradation in Alaskan lowland forests INTERSPECIFIC RESOURCE PARTITIONING IN SYMPATRIC URSIDS