STRESS RESPONSES OF SALIX BOREALIS TO POLLUTION AND DEFOLIATION

1. Morphological characters of Salix borealis were monitored during 19 94-96 at 10 sites along a transect crossing the heavily polluted surro undings of Severonikel smelter in NW Russia, and analysed with respect to pollution load and density of the principal herbivore, the leaf be etle Melasoma lapponica. 2. Leaf size and shoot growth increased and l eaf pubescence decreased with an increase in pollution, whereas variat ion in other characteristics was not related to pollution load. 3. Lea f fluctuating asymmetry (FA) and leaf pubescence increased with an inc rease in herbivory, whereas variation in other characters was not rela ted to foliar damage. 4. A field experiment demonstrated that leaf FA and pubescence were high in the year after defoliation. 5. The data on leaf FA, a non-specific stress indicator, suggest that for the extant individuals of S. borealis, defoliation resulted in detectable stress , whereas long-lasting severe pollution by sulphur dioxide and heavy m etals caused no measurable stress response and may even stimulate grow th of leaves and shoots. 6. Leaf FA of woody plants may serve as an ea rly indicator of the biotic stress caused by herbivory, which expands the use of FA as a tool in helping to compare the relative strengths o f different stressing agents.