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The extension of growing season at high northern latitudes seems increasingly clear from satellite observations of vegetation extent and duration. This extension is also thought to explain the observed increase in amplitude of seasonal variations in atmospheric CO2 concentration. Increased plant respiration and photosynthesis both correlate well with(More)
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(More)
Recent overviews have suggested that the relationship between species richness and productivity (rate of conversion of resources to biomass per unit area per unit time) is unimodal (hump-shaped). Most agree that productivity affects species richness at large scales, but unanimity is less regarding underlying mechanisms. Recent studies have examined the(More)
Global vegetation models predict that boreal forests are particularly sensitive to a biome shift during the 21st century. This shift would manifest itself first at the biome's margins, with evergreen forest expanding into current tundra while being replaced by grasslands or temperate forest at the biome's southern edge. We evaluated changes in forest(More)
[1] Tree rings have been used to both reconstruct past climate, and to estimate and project carbon uptake of forest ecosystems. Here we show that large groups of trees of the dominant tree species within widely-distributed circumpolar forest sites show opposing growth trends during recent warming. These opposing growth trends are present at a sub-chronology(More)
Research Interests Thresholds, transitions and associated timescales of the Earth System. Coastal interactions and impacts. Awards Department of Commerce Silver Medal (2013) Team award " for the development and application of NOAA's first comprehensive Earth System Models that couple the carbon cycle and climate to project changes. " (in review): Drivers of(More)
Changes in boreal climate of the magnitude projected for the 21st century have always caused vegetation changes large enough to be societally important. However, the rates and patterns of vegetation change are difficult to predict. We review evidence suggesting that these vegetation changes may be gradual at the northern forest limit or where seed dispersal(More)
  • P Hennon, D D 'amore, D Wittwer, A Johnson, P Schaberg, G Hawley +3 others
  • 2006
Yellow-cedar (Chamaecyparis nootkatensis) is a valuable tree species that has been experiencing concentrated mortality known as yellow-cedar decline on 200,000 ha of largely pristine forests in Southeast Alaska. Mature trees that regenerated and grew during the Little Ice Age have been dying on low elevation sites with wet soils and open canopies for about(More)
335 Prey change behaviour with predation threat, but demographic effects vary with prey density: experiments with grasshoppers and birds 349 Increases in the flux of carbon belowground stimulate nitrogen uptake and sustain the long-term enhancement of forest productivity under elevated CO 2 358 Predator-driven component Allee effects in a wild ungulate(More)
  • M Wilmking, M Hallinger, R Van Bogaert, T Kyncl, F Babst, W Hahne +4 others
  • 2012
Woody plants growing in seasonal climates normally form one growth ring each year. However, under severe stress conditions they may not complete annual wood production all the way down to the root collar resulting in continuously missing outer rings at lower stem sections (CMORs). Here we test whether CMORs occur at different distributional margins of woody(More)