Longer, warmer but less productive: Decreases in performance in alpine shrub Salix herbacea with earlier snowmelt

Background/Question/Methods

Earlier snowmelt and warming temperatures due to climate change are expected to strongly impact alpine ecosystems and associated plant communities, and thus it is critical to understand how these environmental changes may alter performance in key species. Salix herbacea is a low clonal dioecious shrub that commonly forms groundcover in both arctic and alpine systems, and occurs in a wide range of microhabitats, from early-exposed ridges to late snowbeds. However, the performance of this species under warming and early snowmelt conditions has never been examined. We investigated a wide range of functional and fitness traits in 480 S. herbacea clones, along their natural elevation and snowmelt microhabitat range over three consecutive growing seasons using a space-for-time substitution, in the eastern Alps near Davos, Switzerland. Elevation change was used to simulate temperature warming and earlier snowmelt was used to simulate a longer growing season. The objectives of this study were to determine whether earlier snowmelt and warmer temperatures are beneficial or detrimental for S. herbacea performance, depending on the trait examined, and whether both sexes respond similarly along these climatic gradients.

Results/Conclusions

Earlier snowmelt was associated with longer development times to all phenological stages (leaf expansion, flowering and fruiting), increased likelihood of both herbivory and fungal damage, and a decrease in total stem number per area. For female shrubs, early snowmelt was associated with an increased flowering rate, but not fruiting, as fruit set decreased with earlier snowmelt. Lower elevation (and thus warmer temperatures) was associated with decreases in total stem number, wood sugar reserves and increases in fruiting.

Earlier snowmelt reduced overall S.herbacea performance in both sexes. Warmer temperatures resulted in more fruit but there is no evidence of increased growth (stem numbers). Under early snowmelt conditions, increased likelihood of leaf damage could lead to long-term performance reductions via seasonal reductions in photoassimilation. Similarly, longer phenological development times could lead to increased exposure to spring frosts or other damages during vulnerable early development stages. Although S. herbacea may allocate more energy to flowering under earlier snowmelt, low fruit set decreases the final fruit production relative to later snowbeds, possibly as a result of spring frosts killing flowers. Under climate change, spring snowmelt is expected to accelerate in alpine ecosystems; under these conditions, we conclude overall performance of S. herbacea will decline.