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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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The boreal forests of North America are undergoing major changes because of the direct effects of global warming and increased CO sub(2) levels. Plant production in the boreal forest is nutrient limited, and we examined how long-term fertilization affected growth of white spruce Picea glauca in the face of these major changes. We conducted a large-scale experiment by fertilizing two 1 km super(2) stands of white spruce in the southwestern Yukon with commercial NPK fertilizer from 1987 to 1994. Tree growth was measured by the width of annual increments in 60 trees from each of 2 control and of 2 matched fertilized 1 km super(2) sites for the period from 1977 to 1997 in a before, during, and after experimental design....
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From 2001 to 2004 we experimentally warmed 40 large, naturally established, white spruce [Picea glauca (Moench) Voss] seedlings at alpine treeline in southwest Yukon, Canada, using passive open-top chambers (OTCs) distributed equally between opposing north and south-facing slopes. Our goal was to test the hypothesis that an increase in temperature consistent with global climate warming would elicit a positive growth response. OTCs increased growing season air temperatures by 1.8°C and annual growing degree-days by one-third. In response, warmed seedlings grew significantly taller and had higher photosynthetic rates compared with control seedlings. On the south aspect, soil temperatures averaged 1.0°C warmer and...
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Various effects on plant growth associated with handling or touching plants are well documented from greenhouse and laboratory studies, but are generally unknown or ignored under field conditions. We examined the prevalence of the effects of handling, at levels typical of many ecological experiments, on aboveground biomass and damage by invertebrate herbivores for a total of 16 common species from three plant communities in western Canada. Significant effects of handling were observed in the alpine meadow and grassland, but not in the boreal forest. Handling reduced aboveground biomass and increased the mean intensity of invertebrate leaf damage for most species. A meta-analysis of the relationship between plant...
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Recent research using repeat photography, long-term ecological monitoring and dendrochronology has documented shrub expansion in arctic, high-latitude and alpine tundra ecosystems. Here, we (1) synthesize these findings, (2) present a conceptual framework that identifies mechanisms and constraints on shrub increase, (3) explore causes, feedbacks and implications of the increased shrub cover in tundra ecosystems, and (4) address potential lines of investigation for future research. Satellite observations from around the circumpolar Arctic, showing increased productivity, measured as changes in ‘greenness’, have coincided with a general rise in high-latitude air temperatures and have been partly attributed to increases...
    map background search result map search result map Evidence for selective caching by arctic ground squirrels living in alpine meadows in the Yukon Evaluating Cloud Contamination in Clear-Sky MODIS Terra Daytime Land Surface Temperatures Using Ground-Based Meteorology Station Observations Science and the St Elias: an evolving framework for sustainability in North America's highest mountains Influence of habitat quality, patch size and connectivity on colonization and extinction dynamics of collared pikas Ochotona collaris Being high is better: effects of elevation and habitat on arctic ground squirrel demography Prevalence and predictability of handling effects in field studies: results from field experiments and a meta-analysis Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon Forage selection by collared pikas, Ochotona collaris, under varying degrees of predation risk Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon, Canada Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities Evidence of Recent Treeline Dynamics in Southwest Yukon from Aerial Photographs Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline Variability, contingency and rapid change in recent subarctic alpine tree line dynamics Climate warming as a driver of tundra shrubline advance Automated content analysis as a tool for research and practice: a case illustration from the Prairie Creek and Nico environmental assessments in the Northwest Territories, Canada Spring and summer monthly MODIS LST is inherently biased compared to air temperature in snow covered sub-Arctic mountains Spring and summer monthly MODIS LST is inherently biased compared to air temperature in snow covered sub-Arctic mountains Climate and nutrient influences on the growth of white spruce trees in the boreal forests of the Yukon Forage selection by collared pikas, Ochotona collaris, under varying degrees of predation risk Climate warming as a driver of tundra shrubline advance Automated content analysis as a tool for research and practice: a case illustration from the Prairie Creek and Nico environmental assessments in the Northwest Territories, Canada Science and the St Elias: an evolving framework for sustainability in North America's highest mountains Evaluating Cloud Contamination in Clear-Sky MODIS Terra Daytime Land Surface Temperatures Using Ground-Based Meteorology Station Observations Being high is better: effects of elevation and habitat on arctic ground squirrel demography Four Decades of Plant Community Change in the Alpine Tundra of Southwest Yukon, Canada Responses of white spruce (Picea glauca) to experimental warming at a subarctic alpine treeline Variability, contingency and rapid change in recent subarctic alpine tree line dynamics Prevalence and predictability of handling effects in field studies: results from field experiments and a meta-analysis Evidence of Recent Treeline Dynamics in Southwest Yukon from Aerial Photographs Evidence for selective caching by arctic ground squirrels living in alpine meadows in the Yukon Influence of habitat quality, patch size and connectivity on colonization and extinction dynamics of collared pikas Ochotona collaris Shrub expansion in tundra ecosystems: dynamics, impacts and research priorities