Spatial and temporal patterns of sulfur and nitrogen in wood of trees across the north central United States

Samples represented 5 forest types across Minnesota, Wisconsin and Michigan. The sulfur to nitrogen ratios of both soil and wood increased from W to E across the sulfate deposition gradient, a trend consistent with evidence that sulfate and other sulfur ions deposited through air pollution are accumulating in various compartments of forest ecosystems in the N-central USA. -from Authors