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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...
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Large lightning-caused fires in the forested areas of Canada and Alaska account for most of the area burnt and are one of the main determiners of the age mosaic of the landscape. Generally such fires occur when positive mid-troposphere pressure anomalies persist for more than ten days during the fire season. Mid-troposphere anomalies are part of teleconnection patterns which are created by internal atmospheric and coupled sea/air dynamics. Large lightning fire occurrence and area burnt data were used to define eight major centres of large fire variability (Fire Regions) in the forested areas of Canada and Alaska between 1959 and 1999. Preferred positions of persistent positive mid-troposphere anomalies correlated...
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Shrubs have increased in abundance and dominance in arctic and alpine regions in recent decades. This often dramatic change, likely due to climate warming, has the potential to alter both the structure and function of tundra ecosystems. The analysis of shrub growth is improving our understanding of tundra vegetation dynamics and environmental changes. However, dendrochronological methods developed for trees, need to be adapted for the morphology and growth eccentricity of shrubs. Here, we review current and developing methods to measure radial and axial growth, estimate age, and assess growth dynamics in relation to environmental variables. Recent advances in sampling methods, analysis and applications have improved...
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