Difference in needle length - A new and objective indicator of pollution impact on Scots pine (Pinus sylvestris)

Needle fluctuating asymmetry (FA) in Scots pine (Pinus sylvestris) was stud ied south of the Severonikel nickel-copper smelter in the Kola Peninsula, R ussia. We measured the difference in length of two needles of the same pair , and calculated FA as the ratio between this difference and the average le ngth of the two needles of this pair. Needle FA did not depend on tree age, distance from the nearest neighbour or branch position within the crown, b ut increased with an increase in branching order. Needles originating in di fferent years (1993-1997) demonstrated among-year variation in FA, which, h owever, was not related to annual fluctuations in SO2 emission by the smelt er. FA increased with decreasing distance from the smelter, and in the site s proximate to the smelter FA was double that found at the most distant (ba ckground) sites. The increase in FA was primarily due to an increased diffe rence in the length of the two needles, and this difference may serve as a practicable indicator of pollution-induced stress in Scots pine.