Disentangling seasonal and interannual legacies from inferred patterns of forest water and carbon cycling using tree-ring stable isotopes

Paul Szejner, William E. Wright, Soumaya Belmecheri, David Meko, Steven Leavitt, James R. Ehleringer, Russell Monson

Research output: Contribution to journalArticle

7 Scopus citations

Abstract

Tree-ring carbon and oxygen isotope ratios have been used to understand past dynamics in forest carbon and water cycling. Recently, this has been possible for different parts of single growing seasons by isolating anatomical sections within individual annual rings. Uncertainties in this approach are associated with correlated climate legacies that can occur at a higher frequency, such as across successive seasons, or a lower frequency, such as across years. The objective of this study was to gain insight into how legacies affect cross-correlation in the δ13C and δ18O isotope ratios in the earlywood (EW) and latewood (LW) fractions of Pinus ponderosa trees at thirteen sites across a latitudinal gradient influenced by the North American Monsoon (NAM) climate system. We observed that δ13C from EW and LW has significant positive cross-correlations at most sites, whereas EW and LW δ18O values were cross-correlated at about half the sites. Using combined statistical and mechanistic models, we show that cross-correlations in both δ13C and δ18O can be largely explained by a low-frequency (multiple-year) mode that may be associated with long-term climate change. We isolated, and statistically removed, the low-frequency correlation, which resulted in greater geographical differentiation of the EW and LW isotope signals. The remaining higher-frequency (seasonal) cross-correlations between EW and LW isotope ratios were explored using a mechanistic isotope fractionation–climate model. This showed that lower atmospheric vapor pressure deficits associated with monsoon rain increase the EW-LW differentiation for both δ13C and δ18O at southern sites, compared to northern sites. Our results support the hypothesis that dominantly unimodal precipitation regimes, such as near the northern boundary of the NAM, are more likely to foster cross-correlations in the isotope signals of EW and LW, potentially due to greater sharing of common carbohydrate and soil water resource pools, compared to southerly sites with bimodal precipitation regimes.

Original languageEnglish (US)
JournalGlobal Change Biology
DOIs
StateAccepted/In press - Jan 1 2018

Keywords

  • cross-correlation
  • drought
  • high-resolution
  • North American Monsoon
  • paleoclimatology
  • precipitation
  • stable isotopes
  • vapor pressure deficit

ASJC Scopus subject areas

  • Global and Planetary Change
  • Environmental Chemistry
  • Ecology
  • Environmental Science(all)

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