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The northern treeline is generally limited by available warmth. However, in recent years, more and more studies have identified drought stress as an additional limiting factor for tree growth in northern boreal forests and at treelines. Three growth responses to warming have been identified: increase in growth, decrease in growth, and nonsignificant correlation of tree growth with climate. Here we investigate the effect of drought stress on radial growth of white spruce at northern treelines along a longitudinal gradient spanning the entire Brooks Range in Alaska. We systematically sampled 687 white spruce at seven treeline sites. Where possible, we sampled three site types at a given site: high-density forest,...
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The extensive boreal biome is little studies relative to its global importance. Its high soil moisture and low temperatures result in large below-ground reservoirs of carbon (C) and nitrogen (N). Presently, such high-latitude ecosystems are undergoing the largest temperature increases in global warming. Change in soil temperature or moisture in the large pools of soil organic matter could fundamentally change ecosystem C and N budgets. Since 1990, we have conducted treeline studies in a small (800 ha) watershed in Noatak National Preserve, northwestern Alaska. Our objectives were to (1) gain an understanding of treeline dynamics, structure, and function; and (2) examine the effects of global climate change, particularly...
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The latitudinal gradient of the start of the growing season (SOS) and the end of the growing season (EOS) were quantified in Alaska (61°N to 71°N) using satellite-based and ground-based datasets. The Alaskan evergreen needleleaf forests are sparse and the understory vegetation has a substantial impact on the satellite signal. We evaluated SOS and EOS of understory and tundra vegetation using time-lapse camera images. From the comparison of three SOS algorithms for determining SOS from two satellite datasets (SPOT-VEGETATION and Terra-MODIS), we found that the satellite-based SOS timing was consistent with the leaf emergence of the forest understory and tundra vegetation. The ensemble average of SOS over all satellite...
This study describes the community, population, and growth dynamics of Alnus tenuifolia (thinleaf alder) and implications for nutrient cycling on the Tanana River floodplains. Through symbiotic N-fixation inputs, alder contributed to soil N accumulation with time. N-fixation itself was likely limited by soil P. Soil N was positively related to alder stem density in early successional stands. Community structure varied along a temporal gradient of changing environmental characteristics, but variations in successional patterns were found. Landscape scale alder recruitment varied temporally and was apparently linked to interactions between geofluvial processes, seed production and dispersal, and herbivory. A widespread...
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Pattern and extent of treeline change using sequential vertical aerial photography in the northern section of the Kluane Ranges of southwest Yukon are examined. One of the most common predictions is that continued global temperature increases will cause the tree-line to advance in elevation and latitude. Comparison of aerial photographs of southwest Yukon indicates significant changes in the spruce forest-shrub tundra transition. Many areas exhibit increased growth of individual spruce without an increase in stand density or an advance in spruce distribution. Increase in the elevational distribution of spruce is observed in comparatively fewer areas, typically in combination with other two types of change.
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Increased light reaching streams as a result of riparian vegetation management is often thought to be responsible for enhanced algal productivity. However, concomitant changes in nutrients and other physical processes confound that interpretation. We manipulated light in two separate experiments to test the role of light as a controlling factor for periphyton productivity and biomass, and to observe invertebrate responses in small streams in central British Columbia, Canada. We did this by adding artificial light to reaches of three forested streams, and in a second experiment we used shadecloth to cover reaches of two streams flowing through clearcuts. Periphyton growth, productivity and composition, and macroinvertebrate...


map background search result map search result map Method for Attenuation of White Phosphorus Contamination in Wetlands Indirect and Long-Term Effects of Fire on the Boreal Forest Carbon Budget RELATIONSHIPS AMONG FIRES, FUNGI, AND SOIL DYNAMICS IN ALASKAN BOREAL FORESTS Experimental increases and reductions of light to streams: effects on periphyton and macroinvertebrate assemblages in a coniferous forest landscape Competitive interactions across a soil fertility gradient in a multispecies forest Alder (Alnus crispa) effects on soils in ecosystems of the Agashashok River valley, northwest Alaska Comment on 'Wetland drying and succession across the Kenai Peninsula Lowlands, south-central Alaska' Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline Spruce beetles and forest ecosystems of south-central Alaska Longitudinal variation of radial growth at Alaska's northern treeline; recent changes and possible scenarios for the 21st century Soil nitrogen transformations and retention during a deciduous to coniferous successional transition Denali National Park and Preserve Landcover Mapping Project Volume 2: Landcover classes and plant associations Evidence of Recent Treeline Dynamics in Southwest Yukon from Aerial Photographs Treeline biogeochemistry and dynamics, Noatak National Preserve, northwestern Alaska Latitudinal gradient of spruce forest understory and tundra phenology in Alaska as observed from satellite and ground-based data Method for Attenuation of White Phosphorus Contamination in Wetlands Experimental increases and reductions of light to streams: effects on periphyton and macroinvertebrate assemblages in a coniferous forest landscape Soil nitrogen transformations and retention during a deciduous to coniferous successional transition RELATIONSHIPS AMONG FIRES, FUNGI, AND SOIL DYNAMICS IN ALASKAN BOREAL FORESTS Denali National Park and Preserve Landcover Mapping Project Volume 2: Landcover classes and plant associations Alder (Alnus crispa) effects on soils in ecosystems of the Agashashok River valley, northwest Alaska Treeline biogeochemistry and dynamics, Noatak National Preserve, northwestern Alaska Comment on 'Wetland drying and succession across the Kenai Peninsula Lowlands, south-central Alaska' Exploring ecological changes in Cook Inlet beluga whale habitat though traditional and local ecological knowledge of contributing factors for population decline Evidence of Recent Treeline Dynamics in Southwest Yukon from Aerial Photographs Spruce beetles and forest ecosystems of south-central Alaska Longitudinal variation of radial growth at Alaska's northern treeline; recent changes and possible scenarios for the 21st century Indirect and Long-Term Effects of Fire on the Boreal Forest Carbon Budget Competitive interactions across a soil fertility gradient in a multispecies forest Latitudinal gradient of spruce forest understory and tundra phenology in Alaska as observed from satellite and ground-based data