EFFECTS OF LIVE TREE FUMIGATION ON NONTARGET VEGETATION

Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) trees, both healthy and infected by Inonotus sulphurascens (Pilat) M.J. Larsen, F.F. Lomb ard, and J.W. Clark (Phellinus weirii sensu lato), were fumigated with chloropicrin or methylisothiocyanate at a site in the Oregon Coast Ra nge. Ten growing seasons later, vegetation cover on plots around treat ed and untreated individuals was evaluated to determine fumigant effec ts on nontarget plants. Total plant cover and individual species cover for Berberis nervosa Pursh and Stokesiella oregana (Sull.) Robins wer e significantly reduced in the chloropicrin treatment plots. The domin ant shrub, Gaultheria shallon Pursh, was little affected in chloropicr in plots. Slightly greater species richness and Rubus ursinus Cham. an d Schlecht. cover in chloropicrin plots were attributed to higher ligh t levels and other factors associated with reduced shrub cover on the treated plots. Multivariate analysis showed little overlap in plant co mmunity structure between chloropicrin-treated and control plots. Dete ction of effects due to the methylisothiocyanate treatment was hindere d by the lack of strictly paired control trees. The results are discus sed in relation to the retrospective nature of the study.