A dendroecological method to examine summertime soil-moisture changes: a case study from North Carolina, USA

Key message

Use of co-occurring species with varying temporal sensitivities to summer soil moisture may be used as a diagnostic to determine summertime drought intensification or amelioration.

Abstract

The use of tree-ring data from co-occurring species with different summertime soil-moisture responses provides an opportunity to evaluate the occurrence and direction of soil-moisture changes. Here, we present a method that compares adjusted latewood growth between longleaf pine (Pinus palustris Mill.) and chestnut oak (Quercus prinus L.) from 1969 to 2018 in the Uwharrie Mountains of central North Carolina, USA. We found that adjusted latewood sensitivity to soil moisture varied between species with the strongest response in September PDSI for longleaf pine (r = 0.47), and July PDSI for chestnut oak (r = 0.61). Large (> 0.20 or < − 0.20) radial growth differences between species occurred during 22 years of the 50-year study period and were strongly correlated with PDSI differences (r = 0.74, p < 0.001), while the correlation with the whole dataset (r = 0.34, p < 0.05) was less sensitive. Major growth difference years were predominately negative (n = 17), suggesting that this method is more effective at detecting summers with decreasing soil moisture between mid and late summer. Overall, these results indicate that a differential response between species with dissimilar latewood formation periods may provide a means to examine potential intermonthly changes in summertime soil-moisture conditions as opposed to a single proxy value (e.g., anomalously dry, or wet) characterizing the entire summer.