Climate-growth relationships for yellow-poplar across structural and site quality gradients in the southern Appalachian Mountains

Forecasted changes in climate across the southeastern US include an increase in temperature along with more variable precipitation patterns, including an increase in the severity and frequency of drought events. As such, the management of forests for increased resistance or resilience to the direct and indirect effects of climate change, including decreased tree- and stand-level productivity, is of interest to natural resource practitioners. Because the sensitivity of tree growth to climate can be moderated by competition, manipulating stand density through silvicultural activities may mitigate the negative effects climate change may have on tree growth and productivity. In this paper, we utilized dendrochronology data, along with long-term forest inventory data, from 134 plots established and subsequently thinned between 1960 and 1963 to analyze the effects of climate on annual tree growth for yellow-poplar (Liriodendron tulipifera L.) across a broad stand structural and site productivity gradient in the southern Appalachian Mountains. Annual basal area increment (BAI) was most related to the Palmer Drought Severity Index (PDSI) during the months of May, June, and July (PDSIMJJ) relative to that of the annual or growing season when structural and site productivity variables were included in the analysis. Annual BAI of trees growing in stands of lower density responded to increases in PDSIMJJ at a faster rate than trees growing in stands of greater density. Conversely, those same trees experienced proportionally greater decreases in BAI at lower values of PDSIMJJ compared to trees in stands of greater density. Annual BAI was positivity related to site productivity, as quantified by site index, with BAI more sensitive to changes in PDSIMJJ on plots of progressively higher site index. Results suggest stand structure as well as measures of productivity should be considered when quantifying climate-growth relationships for forest tree species. Such information could not only aid in the identification of stands most susceptible to reduced growth, but also be used to develop site- or stand-specific silvicultural prescriptions focused on promoting resilience or resistance under a changing climate.