Snowpack‐ and Soil Water Content‐Related Hydrologic Indices and Their Association With Radial Growth of Conifers in the Sierra Nevada, California

Abstract

The utility of a high-resolution snow-hydrologic model to derive climatological indices that describe the variability in radial growth of four conifer species in two Sierra Nevada sites is presented herein. Nine annual indices associated with radial growth were developed to represent the winter dormancy, characteristics of the snowpack and soil water content, and the duration of the seasons. Site chronologies of earlywood (EW) and latewood (LW) ring widths were developed for mountain hemlock (Tsuga mertensiana), red fir (Abies magnifica), white fir (Abies concolor), and ponderosa pine (Pinus ponderosa) at two sites on leeward and windward slopes. The signal strength for annual climatological indices derived from model output was tested with correlation and regression, in combination with principal components analysis. Results show significant snow-related climate signal in the tree-ring data, with substantial differences between species and between EW and LW. Dependence on previous year's snow and soil moisture (a lagged response) were found for EW of hemlock and red fir. The primary EW-LW signal contrast for those species is a shift toward dependence on current-year moisture conditions for LW, especially for red fir. Lagged climate response was less evident for white fir and ponderosa pine. Regression of tree-ring series on principal components of climatological indices showed a stronger average signal in EW (R 2 = 0.48) than in LW (R 2 = 0.35). Differences in tree-ring hydrologic signal at the two sites are attributed to microclimate and contrasts in snow regime. Results attest to the hydrologic model usefulness for investigating temporal relationships between tree rings and local climate.

Compensation effect of winter snow on larch growth in Northeast China

“…Tree growth of larch forests in Northeast China is susceptible to variations in spring precipitation and winter snow depth. Studies consistently report an increasingly critical role of preceding-season water supply to the subsequent growing-season tree growth and xylogenesis in diverse temperate regions (Ren et al 2018;Ren et al 2015;Shamir et al 2020). The onset of xylogenesis in drought stressed temperate forest was clearly triggered by a threshold-based precipitation accumulation, and spring precipitation affects the formation of the first row of early-wood vessels in water-limited forests (Zhang et al 2019b).…”

“…Winter snow emerges as an important driver of subsequent tree growth by regulating a range of ecosystem processes, yet these processes are often overlooked when considering the impacts of future climate on forest function. These processes include an increase in soil moisture content, which could partially compensate water loss caused by drought during the growing season (Potopova et al 2016;Shamir et al 2020), insulation effects of snow, which reduce winter damage to the shallow roots of trees (Blume-Werry et al 2016;Reinmann and Templer 2016;Reinmann and Templer 2018;Wipf and Rixen 2010;Wipf et al 2009;Reinmann et al 2019), and regulation of the soil nutrient cycles (Wu 2018). The contributions of these different processes mediated by winter snow to tree growth are, however, heterogeneous among diverse bioclimatic regions.…”

“…The contributions of these different processes mediated by winter snow to tree growth are, however, heterogeneous among diverse bioclimatic regions. Increasing attention has been focused on the hydrothermal regulations of winter snow and its lagged effects on subsequent tree growth (Wang et al 2018;Wu et al 2018b;Zhang et al 2017;Zhang et al 2016a;Shamir et al 2020), particularly in facing a warmer and drier climate regime in many temperate regions. Snow cover/depth acts as a uniquely sensitive climate variable in response to a rapidly changing climate, which depends on temperature and precipitation at a variety of temporal and spatial scales (Hamlet et al 2005).…”

“…Soil water replenishment from winter snowmelt may exert positive effects on subsequent growing-season tree growth, although the effects of winter snow on tree growth are dependent on the background climate condition (e.g., snow depth and monsoon regime) and local edaphic properties (Shamir et al 2020;Mcllroy and Shinneman 2020). In temperate regions dominated by a monsoon climate, summer precipitation is the main water source for tree growth, but the enhanced demand for evapotranspiration linked to higher temperatures in this season may lead to intensified drought stress (Grossiord et al 2020).…”

“…Despite improved understanding of tree growth responses to variations in growing-season climate, little is known regarding how and to what extent winter snow will compensate for the subsequent growing-season tree growth in diverse bioclimatic regions already suffering or prone to seasonal drought stress (Ladwig et al 2016;Zhang et al 2018;Shamir et al 2020;Davis and Gedalof 2018;Pederson et al 2011). It is likely that these mechanisms balance out differently for different species and microsite environmental conditions.…”