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TitleNitrogen isotopes of individual tree-ring series - the validity of middle- to long-term trends
AuthorSavard, M MORCID logo; Marion, J; Bégin, C
SourceDendrochronologia vol. 62, 125726, 2020 p. 1-7,
Alt SeriesNatural Resources Canada, Contribution Series 20190548
PublisherElsevier GmbH
Mediapaper; on-line; digital
File formatpdf; html
SubjectsScience and Technology; environmental geology; Nature and Environment; nitrogen; Boreal Forest Region; Pollution
Illustrationslocation maps; graphs; tables; plots
ProgramEnvironmental Geoscience Sources
Released2020 06 25
AbstractAlthough requiring laborious analytical treatment, tree-ring series of nitrogen isotopes (d15N) have gained popularity amongst researchers for their potential as environmental indicators as anthropogenic emissions increase globally with potential effects on forest N cycles. Previous studies suggested that tree-ring series correlate with climatic and air quality parameters. However, none discussed the level of replication required for expressing the population signals of specific species of trees. In this investigation, we studied 27 white spruce trees from two sites under distinct environmental conditions to evaluate the appropriate protocol for preparing consistent tree-ring d15N series. The produced series indicate that high frequency (short-term, <7 years) d15N changes at a replication as high as 10 trees cannot serve environmental purposes. Conversely, the low frequency (middle-, 7-15 years, to long-term, > 15 years) d15N trends show coherence between arithmetic means of individual series at replication levels as low as three trees, whereas middle-term pooled trends do not perform as coherently. The low frequency mean trends of individual series obtained for the two sites suggest that local biogeochemical soil conditions modified by anthropogenic emissions modulate the d15N responses in trees. Hence, we propose that long-term tree-ring d15N series constitute reliable environmental indicators.
Summary(Plain Language Summary, not published)
Tree-ring series of nitrogen (N) isotopes have attracted research interest for their potential as environmental indicators because anthropogenic emissions increase globally with potential effects on forest N cycles. No previous isotopic studies discussed the number of trees required to represent adequately a specific forest stand. Here, we studied 27 spruce trees from the oil sands and coal-fired power plants regions of Alberta, under distinct environmental conditions, so to find the right protocol for preparing consistent tree-ring isotopic series. Our results indicate that the short-term isotopic changes of 10 trees are inconsistent. Conversely, the long-term isotopic trends show coherence between means of individual series with as few as three trees, whereas the series of tree rings combined before their analysis are not as consistent. The long-term means of individual series obtained here suggest that local soil conditions modulate the isotopic responses of spruce to anthropogenic emissions. Thus, we propose that the long-term averages of individual isotopic series of tree rings constitute reliable environmental records.

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