Testing for effects of stump fumigation with chloropicrin on vegetation in an early seral Douglas-fir stand

The biocide chloropicrin has been suggested for the control of laminated root rot (caused by Phellinus weirii (Murr.) Gilb.), a widespread and economically important disease of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) forests. This study investigated the effects of chloropicrin use on vegetation. A 65-year-old stand in northwestern Washington dominated by Douglas-fir was harvested by clear-cutting in 1988. At time of harvest, the stand was severely affected by laminated root rot. After harvest, plots were either left unfumigated or fumigated with 3.0-18.2 kg of chloropicrin per 0.04 ha. We used multivariate analyses to investigate the effect of chloropicrin on the abundance of vegetation, accounting for pretreatment plot differences. Five years after harvest and fumigation, no significant differences in vegetation composition or cover were found. Chloropicrin fumigation significantly increased diversity (Hillʹs measure) but not richness. Of the 10 most abundant species, only two showed significant effects: higher levels of chloropicrin application led to lower Veronica serpyllifolia L. var. serpyllifolia cover and to more Linnaea borealis L. cover. The power of statistical tests to detect effects of chloropicrin on vegetation was high (0.75-0.99) for large effect sizes, lending confidence to the conclusion that chloropicrin use caused few prominent adverse effects.