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Abstract In eastern Canada, Black spruce (Picea marianaMill. B.S.P.) grows in a wide variety of climates, from maritime-oceanic conditions near the Labrador Sea, to more continental climates, inland. Along this gradient, timing and provenance of heat and moisture that support growth are uncertain, weakening our capacity to predict the response of boreal ecosystems to climate variability. Here, we measured the stable oxygen isotopic composition of black spruce tree-ring cellulose at three sites in eastern Canada and provide evidence of a rapid decrease of Labrador Sea’s influence on adjacent ecosystems. Our results report a landwards decrease in the oxygen isotope composition of both tree-ring cellulose (δ18OTRC) and precipitation water (δ18Op). We also reveal a rapid landwards decoupling betweenδ18OTRCvariability (1950-2013), maximum temperature and Sea Surface Temperature variations over the Northwest Atlantic. Thus, despite their apparent ecological homogeneity, eastern Canada’s black spruce ecosystems rely on heterogeneous sources of heat and moisture.
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Nonlinear Growth and Physiological Responses of White Spruce at North American Arctic Treeline
Abstract Much is still unknown about the growth and physiological responses of trees to global change at the northern treeline. We combined tree‐ring width data with century‐long stable carbon and oxygen isotope records to investigate growth and physiological responses of white spruce at two treeline sites in the Canadian Arctic to concurrent increases in temperature, atmospheric CO2concentration (ca), and decline in sea ice extent over the past century. The tree‐ring records were assessed during three periods with contrasting climatic conditions: (a) the early 20th century warming, (b) the 1940–1970 cooling period, and (c) the anthropogenic late 20th century warming period. We found opposing growth trends between the two sites, but similar carbon isotope discrimination (Δ13C) and intrinsic water‐use efficiency (iWUE) trajectories. While tree growth (defined as basal area increment) increased at the site nearer to the Arctic Ocean during the 20th century following the rise in temperature and sea ice loss, growth declined after 1950 at the more interior site. At both sites, Δ13C slightly increased over these periods. However, trees showed a nonlinear response to increasedca, shifting after 1970 from a passive stomatal response (i.e., no changes iniWUE) to an active response (i.e., a moderate ∼12% increase iniWUE). Further, our isotope‐based findings do not support the idea that temperature‐induced drought stress caused the divergent growth trends at our treeline sites. This study thus highlights nonlinear and complex physiological and growth adjustments to concomitant changes in temperature, sea ice extent, andcaover the last century at the northern treeline.
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- PAR ID:
- 10409264
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 128
- Issue:
- 4
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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