Silver birch plantations can remove heavy metals from former farmland

Silver birch stands planted on former agricultural land can absorb harmful heavy metals from the soil, helping to clean it over time, a study by Estonian University of Life Sciences researchers reported by ERR has found.

Researchers examined soil, bark and wood from 11 birch stands established on former fields or grasslands more than 20 years ago. They measured chromium, copper, iron, manganese and zinc. When trees are harvested and the wood removed, some of the metals taken up by the trees are removed from the land as well.

The trees did not store all metals in the same way. Zinc and manganese accumulated particularly in the bark. Metal uptake was influenced more by soil acidity and its phosphorus and potassium content than by metal levels in the topsoil.

Higher metal concentrations in the soil did not significantly restrict birch growth in the study. However, the researchers cautioned that the measured levels may have been below those that harm trees, and heavier contamination could still affect growth. Compared with hybrid aspen stands of similar age, the birch stands generally removed more metals from the soil.

All the stands grew on fertile mineral soils. Soil metal levels differed between forest site types, but the differences were not statistically significant. Iron and manganese were the most abundant of the metals studied.