Removing the transition wood carryover effect from latewood blue intensity to improve climate signals from Tsuga canadensis in the eastern United States

Tree rings have long provided critical insights into past temperature variability and extremes, helping to contextualize recent warming trends. In recent decades, blue intensity (BI), a light-based reflectivity method, has become a widely used and cost-effective tool for estimating densiometric ring growth, often yielding stronger temperature signals than radial width measurements. However, certain aspects of BI remain underexplored, particularly the potential of a carryover effect from transition wood blue intensity (TBI) on latewood blue intensity (LWBI). In this study, we analyzed Tsuga canadensis (eastern hemlock) to determine whether removing the carryover effect of TBI improves the climate signal embedded within LWBI. Across 14 sites, TBI was significantly correlated with LWBI (mean r = 0.42, p < 0.01), suggesting a carryover effect. By removing the influence of TBI, the adjusted LWBI (LWBIa) reduced spring correlations (March-April; meanΔ = −0.05) while increasing correlations with August temperatures (meanΔ = +0.04) and growing season average Tmax (May-September; meanΔ = +0.04). LWBIa outperformed DeltaBI, with 93 % of sites showing improved correlations with August Tmax compared to 57 % for DeltaBI. However, LWBIa reduced correlations for September, limiting improvements in late summer averages (August-September). These findings demonstrate that adjusting LWBI by accounting for the carryover effect of TBI can improve temperature sensitivity for August and the growing season, potentially enhancing the accuracy of BI-based reconstruction models. Further studies are needed to evaluate this adjustment across other species and regions to fully assess its broader applicability.