Trace of negative changes in environment recorded in cores of trees growing near busy city roads in Poznań, Poland – dendromonitoring of urban pollution

Dendromonitoring helps answer the question of how polluted cities are and how this pollution will change over the years. However, due to many possible over-interpretations of the obtained results, it is necessary to understand the deposition processes of pollutants in trees thoroughly. Thus, the aim of this study was to determine the mineral composition of the wood of 3 common deciduous tree species: Norway maple (Acer platanoides L.), silver birch (Betula pendula Roth.), and black poplar (Populus nigra L.) growing near the busiest roads in Poznań, Poland. The research material consisted of core fragments containing the annual increments collected at the breast height of living trees. The content of 22 elements (Al, Ba, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Mo, Na, Nd, Ni, Pb, Pr, Rb, Sb, Sr, Ti, Tl, and Zn) in the obtained samples together with the determination of the number of annual increments and density of 3 cm wood fragments were presented. The obtained results indicated an overall increase in the content of determined elements from the pith to the cambium layer. The range of the examined elements was extensive, and it was not found that one particular species accumulated the most of all the elements. Acer platanoides accumulated the highest concentration of 13 (Ca, Cd, Cu, Fe, K, Mg, Mo, Na, Nd, Ni, Pb, Sr, and Ti), B. pendula of 3 (Ba, Mn, and Zn), and P. nigra of 6 (Al, Cr, Pr, Rb, Sb, and Tl) elements. Despite the growth of individuals of the same species in different parts of the city, a general trend associated with the increase in the content of most elements was observed. We can assume that the concentration increase indicated in our study reflects the increasing degree of pollution in the urban environment over 30 years.