On the declining relationship between tree growth and climate in the Midwest United States: the fading drought signal
- 559 Downloads
Tree rings are widely considered to be a reliable proxy record of variations in climate and soil moisture. Here, using data from the Midwest United States (US), we provide documentation of a deteriorating relationship between radial tree growth and drought that is consistent across multiple species and locations. We find that traditional methods for drought reconstructions produce models that have rapidly declining validation statistics in recent decades. Split-sample calibration-verification that uses the first and second halves of the record can be problematic, as those two samples may not represent a sufficiently wide range of soil moisture conditions. To investigate this problem, we develop a randomized validation procedure that generates an empirical distribution of calibration and validation statistics. We place validation statistics derived from traditional methods in the generated distribution and compare them to a stratified approach that ensures each calibration model is composed of a sample that includes both dry and wet years. We find that the deteriorating relationship between tree growth and soil moisture is an artifact of the absence of drought over an extended period of time. A model that forces each calibration period to contain extreme drought years is statistically validated.. Nonetheless, if the current pluvial continues in the Midwest US, the linear relationship between tree rings and soil moisture will likely continue to deteriorate to the point where tree rings in the region will have a reduced ability to estimate past drought conditions.
KeywordsTree Growth Tree Ring Validation Statistic Extreme Drought Standardize Precipitation Evapotranspiration Index
We thank Dale Weigel at the U.S. Forest Service, personnel at the Indiana Division of Natural Resources Division of Nature Preserves, and the Nature Conservancy, and Dr. Matthew Therrell for assistance to access our study sites. Thanks to James Dickens, Trevis Matheus, Kayla Pendergrass, Karly Schmidt, Matthew Wenzel, Nicolas Batchos, and Luke Wylie for field assistance and Kayla Pendergrass for lab assistance. We also are grateful to Dr. Stockton Maxwell, Dr. Bryan Black, and Dr. Evan Larson for thoughtful discussions that improved this manuscript. Lastly, we thank three anonymous reviewers for their insightful comments and Dr. Michael Mastrandrea for organizational advice.
- Allen CD, Macalady AK, Chenchouni H, Bachelet D, McDowell N, Vennetier M, Kitzberger T, Rigling A, Breshears DD, Hogg ET, Gonzalez P (2010) A global overview of drought and heat-induced tree mortality reveals emerging climate change risks for forests. For Ecol Manag 259:660–684CrossRefGoogle Scholar
- Choat B, Jansen S, Brodribb TJ, Cochard H, et al. (2012) Global convergence in the vulnerability of forests to drought. Nature 491:752–755Google Scholar
- Cook ER, Krusic PJ (2004) North American summer PDSI reconstructions. IGBP PAGES/World Data Center for Paleoclimatology Data Contribution Series, 45Google Scholar
- Cook ER, Peters K (1981) The smoothing spline: a new approach to standardizing forest interior tree-ring width series for dendroclimatic studies. Tree-Ring Bull 41:45–53Google Scholar
- D’Arrigo RD, Kaufmann RK, Davi N, Jacoby GC, Laskowski C, Myneni RB, Cherubini P (2004) Thresholds for warming-induced growth decline at elevational tree line in the Yukon territory, Canada. Glob Biogeochem Cycles 18:GB3021Google Scholar
- De Grandpré L, Tardif JC, Hessl A, Pederson N, Conciatori F, Green TR, Oyunsanaa B, Baatarbileg N (2011) Seasonal shift in the climate responses of Pinus sibirica, Pinus sylvestris, and Larix sibirica trees from semi-arid, north-central Mongolia. Can J For Res 41:1242–1255Google Scholar
- Fritts HC (1976) Tree rings and climate. Academic Press, New YorkGoogle Scholar
- Maxwell JT (2016) The benefit of including rarely used species in dendroclimatic reconstructions: a case study using Juglans nigra in south-central Indiana. Tree-Ring Res, USAGoogle Scholar
- Palmer WC (1965) Meteorological Drought, Weather Bureau Research Paper No. 45. Washington, DC: US Department of CommerceGoogle Scholar
- Saladyga T, Maxwell RS (2015) Temporal variability in climate response of eastern hemlock in the Central Appalachian Region. Southeast Geogr 55:143–163.Google Scholar
- Wahl ER, Smerdon JE (2012) Comparative performance of paleoclimate field and index reconstructions derived from climate proxies and noise-only predictors. Geophys Res Lett 39:L06703Google Scholar