Climate sensitivity of Norway spruce inferred from blue intensity and tree-ring width

Abstract

In high-mountain Norway spruce stands, contrasting tree health and strong within site growth divergence may alter climate sensitivity and obscure climate reconstructions when trees are analysed together. We tested whether blue intensity (BI) chronologies, developed for all trees or separately by health status, provide stronger climatic signals than tree-ring width (TRW) chronologies. We established 12 plots and sampled neighbouring canopy trees of similar size and social position but contrasting health status (healthy vs. declining or dead). High resolution tree-ring images were used to develop indexed TRW and BI chronologies and assess their temperature sensitivity. During 1961–1990, BI showed stronger correlations with temperature than TRW, whereas in recent period 1991–2022 TRW became more strongly related to temperature in healthy trees. In declining or dead trees, BI retained a stronger temperature signal than TRW. These findings indicate that tree health and recent warming may alter the climate-growth relationships and that BI and TRW provide complementary information for climate reconstruction.