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Frequencies of multivariate air masses drive global tree growth
  • Cameron C Lee,
  • Matthew Paul Dannenberg
Cameron C Lee
Kent State University

Corresponding Author:cclee@kent.edu

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Matthew Paul Dannenberg
University of Iowa
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Surface meteorological conditions in the midlatitudes are embedded within and affected by synoptic-scale systems, including the movement and persistence of air masses (AMs). Changes in the frequencies of different AMs over the past several decades could potentially have large effects on ecosystems: each organism is exposed to the synergistic effects of the entire suite of atmospheric variables acting upon it – an inherently multivariate environment – which is best captured using AMs. Utilizing a global-scale AM classification system and a global network of tree-ring widths, we investigate how variation in AM frequency impacts tree growth at over 900 locations. We find that AM frequencies are well-correlated with tree growth, especially in the 12-month period from July in the year prior to growth through June in the year of growth. The most important AMs are Dry-Warm and Humid-Cool AMs, which exhibit average correlations of ρ=-0.4 and ρ=+0.4 with global tree growth, respectively, among commonly sampled tree species, with correlations at some sites exceeding ρ=+/-0.8 in some seasons. Compared to empirical models based solely on temperature and precipitation, modeling using only AM frequencies proved superior at nearly 60% of the sites and for over 80% of the well-sampled (n≥10) species. These results should provide a foundation for using AMs to improve forecasts of tree growth, tree stress and wildfire potential. Long-term reconstructions of AM frequencies back several centuries may also be feasible using tree-ring data, which will help contextualize and temporally extend multivariate perspectives of climate change that utilize such air masses.