Dendrochronological evidence for snowpack‐induced growth limitation in ponderosa pine ( Pinus ponderosa ) in central Idaho

Abstract

Snowpack regimes are projected to change in western North America in the coming decades. Average spring snowpack disappearance date is predicted to occur earlier, and snow‐to‐rain transition will become more common across the region. There is uncertainty about how forests will respond to these changes and the potential heterogeneity of this response across species and topography. In the absence of experimental data, growth–climate correlations from tree‐ring data offer an indirect window into tree physiology and may enable eco‐physiologists to develop new questions about the physiological mechanisms behind the relationships observed in the dendrochronological record. We analyzed new and existing tree‐ring data from ponderosa pine ( Pinus ponderosa ) from four sites in central Idaho, USA, to examine relationships between radial growth and snow‐water equivalence (SWE) data from SNOTEL for the period 1981–2023, and radial growth, precipitation, and temperature data from Parameter‐elevation Regressions on Independent Slopes Model (PRISM) for the period 1920–2023. Our analysis suggests an elevation‐dependent combination of current‐water‐year spring snowpack growth limitation during high‐SWE springs and an unexpected positive biological memory effect of previous‐water‐year SWE on subsequent year ring width at sites above 1500 m ( r  = 0.33–0.54 by site; p  < 0.05). We posit that this effect may result from carbon sink limitation followed by release. Future field experiments that manipulate snowpack are needed to confirm or refute these physiological explanations so that we can better understand the impacts that the projected decline in snowpack may have on this important conifer species in coming decades.