Fluctuating asymmetry of birch leaves increases under pollution impact.
Fluctuating asymmetry (FA) of birch (Betula spp.) leaves collected along 4 pollution gradients in NW Russia and Finland was assessed by measuring the difference in width between right and left halves of the leaf. B. pubescens was sampled at all sites (as the mountain birch B. pubescens subsp. tortuosa [B. tortuosa] in the Kola Peninsula, and the white birch B. pubescens subsp. pubescens at other sites), and silver birch (B. pendula) in Finland and in the St. Petersburg region. All these birches produce 2 kinds of shoots - short (brachiblasts, with 2-5 small leaves from the previous year) and long (auxiblasts, with 5 or more large leaves depending on the current year climate). FA of leaves was not related to tree diameter, and values for long and short shoots of the same tree were correlated. FA of B. pendula and the 2 subspecies of B. pubescens, decreased hyperbolically with distance away from 4 sources of aerial emission which differed in amounts and composition of pollutants. The extent of the zone of increased FA was higher around polluters which produced more emissions. FA of leaves sampled around 2 smelters was positively related to foliar nickel concentrations, and regressions from these 2 sites had similar slopes and intercepts. The data suggest that FA of birch leaves may represent a convenient indicator for rapid assessment of environmental quality.