Urban Trees as Environmental Archives: Multi‐Decadal Trends in Tree‐Ring Chemistry and Growth of Picea abies and Quercus robur Along Major Roads in Poznań, Poland

Given the rapid growth of urban areas, when assessing environmental changes, it is essential to use indicators that are permanently integrated into the urban landscape. Trees continuously record the impacts of human activities in their structure. For this reason, the aim of this study was to analyze the content of specific elements in the annual growth rings of Picea abies and Quercus robur growing along roads in Poznań, Poland. The goal was to assess changes in environmental pollution levels in an urban area. The collected materials were characterized by annual ring width and density to assess how varying urban conditions influenced tree growth. In both P. abies and Q. robur , notable exceptions to the trend of decreasing annual ring width with tree age were observed, largely due to significant changes in the urban environment. An analysis of the elemental concentration in annual ring groups revealed a general increase, particularly in the sapwood of both tree species. For the oldest Q. robur , this increase was linked to the rapid industrial development in the 1950s, along with a marked decrease in precipitation and an increase in annual temperatures in Poznań. Variations in the elemental content among groups of tree rings likely reflect site‐specific microenvironmental factors, including differences in local hydrology, surface sealing, and proximity to traffic‐related emission and deposition pathways. The narrowing of these growth rings, along with a marked increase in element concentrations on the cambial side, clearly indicates worsening urban environmental degradation.