Updated dendrochronology and axial variation of climatic sensitivity in Sequoiadendron giganteum

Abstract

Key message

Dendroclimatic sensitivity varies by axial position for Sequoiadendron giganteum: negative correlations with June temperature strengthen with height, while positive correlations with snow water are strongest in the lower trunk.

Increment cores collected along trunks of mature Sequoiadendron giganteum provide new and updated ring-width chronologies ideal for assessing how height above ground affects sensitivity of radial growth to climatic variation. Chronologies from 61 living trees at nine locations across the geographic distribution span 1973 yr. Analyses of subsets of 18–44 trees reveal that correlations between radial increments and climate (temperature, water availability) vary with axial position. Negative correlations with maximum and minimum June temperature intensify with height and are strongest at the highest position analyzed (60 m above ground). Sensitivity to the hydroclimate variable of April-1 snow water equivalent is stronger at lower trunk positions (10 m) compared to breast height or the upper trunk, and a similar relationship is identified for the standardized precipitation evapotranspiration index using a 12-month window ending in September. Drought-induced low-growth years computed as radial increment relative to the mean of 10 yr before and after are more weakly expressed at breast height compared to higher on the trunk (10–60 m). Analysis of regional upper (maximum core height = 87 m) versus lower trunk (above buttress) chronologies corroborate differing inter-annual correlations with climate depending on height above ground. Accounting for axial variation in dendroclimatic sensitivity can maximize the quality of environmental reconstructions using tree rings and improve biophysical understanding of Sequoiadendron, especially in the context of an increasingly arid climate.