Fluctuating asymmetry of birch leaves increases under pollution impact

1. Fluctuating asymmetry (FA) of birch leaves collected along four pollution gradients in NW Europe was assessed by measuring the difference in width between right and left halves of the leaf. 2. FA of leaves was not related to tree diameter, and values for long and short shoots of the same tree were correlated. 3. FA of silver birch Betula pendula and two subspecies of B. pubescens, white birch B. pubescens ssp. pubescens and mountain birch B. pubescens ssp. tortuosa, decreased hyperbolically with distance away from four sources of aerial emission which differed in amounts and composition of pollutants. 4. The extent of the zone of increased FA was higher around polluters which produced more emissions. 5. FA of leaves sampled around two copper-nickel smelters was positively related to foliar nickel concentrations, and regressions from these two sites had similar slopes and intercepts. 6. The data suggest that FA of birch leaves may represent a convenient indicator for rapid assessment of environmental quality.