Advanced snowmelt affects vegetative growth and sexual reproduction of Vaccinium myrtillus in a sub-alpine heath

Question In cold regions, snow cover duration is expected to decrease, especially in spring, as a consequence of climate warming. We investigated effects of changes in timing of snowmelt in relation to weather conditions on Vaccinium myrtillus, a dominant shrub in heath vegetation. We tested the hypothesis that advanced snowmelt will enhance shrub growth in years with few frosts, but will reduce shrub growth in years with frequent frosts. Location A sub-alpine heath in the Northern Apennines (Italy). Methods We carried out two experiments. In the main experiment, snow was added to (+S) or removed from (S) experimental plots in spring of three growing seasons (20042006), with a mean delay in snowmelt timing of about 2wk from S to +S. In a companion experiment, we simulated a freezing event in late spring 2004. Results During the snowmelt period, the S plants experienced 610 more frost events, compared with +S and unmanipulated controls (C) in 2004 and 2005, but not in 2006. In the first 2yr leaf production, leaf expansion and flowering were all significantly reduced in the S plants, while shoot elongation was unaffected. In the companion experiment with artificial frost V.myrtillus presented similar responses. Conversely, the manipulations of snow did not affect either the hydric or nutrient status of plants and soils. Conclusions The results overall support our hypothesis, as shown by the differing effects of snow depth and timing of melt on V.myrtillus in the 3yr. Spring frost was the cause of reduced growth and reduced flower production in 2004 and 2005. However, advanced snowmelt will not decrease the cover of this dominant species. Therefore, the structure and species dominance patterns in sub-alpine heath are not expected to change significantly in response to reduced snow cover. Support for this conclusion is provided by the capacity of V.myrtillus to recover vegetatively from frost injury through stimulated shoot elongation, and by the low importance of sexual reproduction for propagating dominant ericaceous shrubs in closed heath communities.