The snow and the willows : the ecological responses of the alpine dwarf shrub "Salix herbacea" to climate change

• Main Author: Wheeler, Julia Anne Charlotte
• Other Authors: Körner, Christian, Hoch, Günter, Myers-Smith, Isla H.
• Format: Thesis
• Language: English
• Published: 2014
• Subjects: Arctic; Climate change; Salix herbacea; Tundra
• Online Access: http://edoc.unibas.ch/diss/DissB_11050; https://edoc.unibas.ch/34906/; https://edoc.unibas.ch/34906/1/wheeler_phd_thesis_final_copy_complete.pdf; https://doi.org/10.5451/unibas-006318079

Current changes in shrub abundance in alpine and arctic tundra ecosystems are primarily driven by warming, changes in snow cover time and shifts in biotic interactions. However, while taller shrub communities are expanding, dwarf shrubs show reductions under climate warming. The aim of this thesis was to disentangle the phenological, growth and fitness response of a widespread prostrate shrub to warming and changes in snowmelt time, investigate shifts between competition and facilitation in communities along environmental stress gradients, and determine trait plasticity in response to snowmelt change. To this end, we investigated phenology, vegetative growth and reproductive traits in Salix herbacea, a widespread, long-lived alpine and arctic prostrate shrub, along its elevational and snowmelt microhabitat range over three years in Davos, Switzerland. To examine environmental drivers of trait variation, community interactions and potential for plastic responses to global changes, we used a space-for-time substitution study, a neighbor removal experiment, and reciprocal transplant experiment. Earlier snowmelt was associated with longer phenological development periods, an increased likelihood of herbivory and fungal damage, fewer stems and no increase in end-of-season wood reserve carbohydrates. Furthermore, while early snowmelt was associated with an increased proportion of flowering stems, the number of fruiting stems was not, as fruit set decreased significantly with earlier snowmelt. Warmer temperatures at lower elevations were associated with decreases in stem number and wood low-molecular weight sugars, and increases in proportion of stems fruiting. In the reciprocal transplant experiment, S. herbacea generally started to grow earlier, but had a longer development time and produced smaller leaves on ridges relative to snowbeds. The phenological changes did not influence clonal or sexual reproduction, but smaller leaves in early-snowmelt sites were associated with reduced sexual reproduction, a potentially ...