Climatic extremes may lead to counterintuitive effects for species and communities. During a record-breaking heat spell in July 2008, we measured wilting, mortality, and subsequent seed set for five upper-montane perennial herbs in the Klamath-Siskiyou Mountains, Oregon, USA..We asked how these measures of plant performance varied with elevation (1500-2000m) and aspect (a warm west slope and a cool north slope of the same mountain).

Results/Conclusions

The proportion of wilted plants increased with elevation on the warm west slope, but showed no relationship with elevation on the cool north slope. Wilted plants were more likely to die over the course of the growing season and this was especially true on the west slope. In addition, a greater proportion of wilted plants on the west slope set seed than did unwilted plants on the west slope or any plant on the north slope. These results suggest that plants at higher elevations are experiencing elevated stress, which is manifested in wilting and higher seed set (severely stressed plants may allocate a greater proportion of resources to reproduction, increasing seed set). Interactions between elevation and aspect may lead to counterintuitive climate effects.