Effects of historical industrial air pollution on European beech trees in Transylvania, Romania

Air pollution significantly endangers forest ecosystems, particularly in cities. As urbanization and industrial activities continue to expand, air quality has decline because of the release of various pollutants from sources like burning fossil fuels, non-ferrous metal processing, mining activities, and increasing road traffic. Our study sites were located in the Copșa Mică area, which was once one of the most heavily industrialized and polluted cities in Europe. We employed a dendrochronological approach to evaluate the effects of pollution on trees, as tree rings can preserve long-term records of environmental changes, including both climate variability and pollution. This information is reflected in the width and chemical composition of the tree rings. This study aims to assess and quantify the negative spatial and temporal effects of local industrial pollution on European beech ( Fagus sylvatica L.) trees. The study quantifies the effects of pollution by measuring radial growth losses in trees affected. Additionally, it examines how local industrial pollution influences the relationship between climatic factors and tree growth, depending on the extent of pollution damage. The period between 1955 and 1990, during which European beech trees were exposed to high levels of air pollution, coincides with the operation of polluting industrial units in the region. During this time, trees in the intensively polluted area experienced growth losses of 31.7% compared to those in unpolluted area, measured by both tree ring width and basal area increment. Radial growth rates around 1990 reveal that trees in the intensively polluted area had a significant increase in growth compared to trees located in moderate and unpolluted areas. This radial growth spurt is attributed to the substantial reduction in pollution levels after 1990. Additionally, the negative effects of air pollution on the dendroclimatic response of trees were evident. In the period 1955-2000 trees in the intensively polluted area exhibited a distinct dendroclimatic response compared to those located in unpolluted areas. In particular, trees in the polluted area showed a negative response to variations in both precipitation and monthly temperature.