Testing the Temporal Stability of the Climate Response of Tree Species at Norris Dam State Park, Tennessee, U.S.A.

Temporal stability of the climate-tree growth relationship means that over time, tree species were responding to a specific climate variable and continue to respond to that variable into the present. The stability of this response is important to test prior to attempting to reconstruct past climate. In this study, I sampled oaks (white oak = Quercus alba L. and chestnut oak = Quercus montana Willd.) and pines (Virginia pine = Pinus virginiana Mill. and shortleaf pine = Pinus echinata Mill.) growing in Norris Dam State Park in eastern Tennessee and tested the temporal stability of these species and their potential for reconstructing past climate. The cores were mounted and sanded, and the tree rings were crossdated and measured. I created chronologies in ARSTAN and analyzed my tree-ring data with DENDROCLIM2002 using regional climate data, which with the use of response and correlation functions and forward and backward evolutionary intervals, tested the temporal stability of the climate-tree growth relationship. Oak was positively correlated with late spring (June) precipitation and pine was positively correlated with spring (May-June) precipitation. Both species were positively correlated with growing season Palmer Drought Severity Index (PDSI), oak with late growing season (June-October) PDSI and pine with early growing season (May-July) PDSI. Oak had a negative relationship with temperature in late spring (June). These relationships are consistent from 1895 to 2015 in correspondence with the instrumental record. The chronologies formed can be used to reconstruct these past climate variables. In the southeast, both stable and unstable relationship between climate and tree growth have been found, which confirms the need to assess temporal stability on a site by site and chronology by chronology basis before reconstructions are attempted.