Observations of copper, zinc, iron and manganese status in western Washington forests

Abstract

Some second-growth stands and plantations of Douglas fir and western hemlock in western Washington are marginally supplied with Fe, Cu and Zn. At some sites, current tissue concentrations of Fe, Cu and Zn are <30, <1 and <10 mg/kg respectively. However, critical tissue concentrations for field conditions in western Washington are not known. Sites with low Cu, Fe and Zn are more common in coastal locations where soils are older, more acidic, and higher in nitrogen and organic matter than many Cascade and Puget Sound lowland soils. In contrast to Fe, Cu and Zn, tissue Mn concentrations in Douglas fir and western hemlock commonly exceed 200 mg/kg, and can reach values as great as 2000 mg/kg. Higher Mn levels are reported at sites in the Cascade mountains. Western red cedar consistently had higher reported tissue Cu and Zn but less Mn than Douglas fir and western hemlock. Douglas-fir samples consistently have higher Zn levels than western hemlock. Both arborescent and herbaceous broadleaf species accumulate higher metal concentrations than conifers. Total and extractable Cu and Zn in most western Washington soils are comparable with worldwide soil averages. Therefore, in most cases, low tissue Cu, Fe and Zn level appears to be related to soil and plant interactions rather than an absolute deficiency. Antagonisms among Al, hydrogen ions and metals in uptake and translocation by Douglas-fir and western hemlock seedlings were demonstrated in solution culture. Low pH and high exchangeable and solution Al may reduce Fe, Cu and Zn uptake and/or availability in western Washington forests.