A historical perspective on divalent cation trends in red spruce stemwood and the hypothetical relationship to acidic deposition

Abstract

Anomalies in the radial concentration trends of Ca²⁺, Mg²⁺, and other divalent cations in the stemwood of red spruce (Picearubens Sarg.) occurred in trees grown in New England, Tennessee, and North Carolina. These anomalies may be assumed to result from changes in sap chemistry. These inferred changes in sap chemistry were the expected result of changes of divalent cation availability in forest soils. The patterns of these anomalies may be interpreted as a signal of a regional mobilization of cations in the rooting zone of red spruce. The anomalous increase in divalent cations present in wood formed in the mid-1900s is coincident both with rapid increases in SO_x and NO_x deposition in eastern North America and with increases in radial growth increment. The anomalous decrease in divalent cations in wood formed in the late-1900s is coincident with declines in radial increment. Comparisons with divalent cation trends in eastern hemlock (Tsugacanadensis (L.) Carr.), Fraser fir (Abiesfraseri (Pursh) Poir.), and yellow birch (Betulaalleghaniensis Britt. = B. lutea Michx.) suggested that these anomalies were not restricted to red spruce. Radial concentration trends of ⁹⁰Sr introduced to the environment through radioactive fallout during the 1950s and 1960s were used to investigate the physiology of these divalent cation concentration anomalies. The distributions of ⁹⁰Sr were also used to estimate the turnover rates for the nutritionally available pools of alkaline earths such as calcium.