Tree-ring variation in western larch (Larixoccidentalis) exposed to sulfur dioxide emissions

Abstract

A tree-ring analysis was conducted to determine the relationship of sulfur emissions from the lead–zinc smelter at Trail, B.C., to radial growth in western larch (Larixoccidentalis Nutt.). Tree cores were collected from five stands known to have been polluted and from three control stands. Age effects were removed from cross–dated ring-width series by fitting theoretical growth curves and, subsequently, tree-ring chronologies were developed for each stand. We assumed that macroclimatic variation was estimated by the average of the control chronologies and two lagged values thereof. These control variables along with annual estimates of sulfur emissions were used in regression models to predict variation in the tree-ring chronologies from each of the polluted stands. Separate analyses were performed for years before and after installation of two tall stacks, for drought and nondrought years, and for years prior to initiation of smelting. In each case following the initiation of smelting, the variation explained by sulfur decreased with distance from the smelter and, concomitantly, the variation explained by the control variables increased with distance. Furthermore, chronology statistics suggested an increase in synchronous high-frequency variation in chronologies from polluted sites that persisted beyond implementation of pollution controls, which reduced emissions 10-fold.