Growth and Phenology of Three Dwarf Shrub Species in a Six-Year Soil Warming Experiment at the Alpine Treeline

Abstract

Global warming can have substantial impacts on the phenological and growth patterns of alpine and Arctic species, resulting in shifts in plant community composition and ecosystem dynamics. We evaluated the effects of a six-year experimental soil warming treatment (+4°C, 2007–2012) on the phenology and growth of three co-dominant dwarf shrub species growing in the understory of Larix decidua and Pinus uncinata at treeline in the Swiss Alps. We monitored vegetative and reproductive phenology of Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum throughout the early growing season of 2012 and, following a major harvest at peak season, we measured the biomass of above-ground ramet fractions. For all six years of soil warming we measured annual shoot growth of the three species and analyzed ramet age and xylem ring width of V. myrtillus. Our results show that phenology of the three species was more influenced by snowmelt timing, and also by plot tree species (Larix or Pinus) in the case of V. myrtillus, than by soil warming. However, the warming treatment led to increased V. myrtillus total above-ground ramet biomass (+36% in 2012), especially new shoot biomass (+63% in 2012), as well as increased new shoot increment length and xylem ring width (+22% and +41%, respectively; average for 2007–2012). These results indicate enhanced overall growth of V. myrtillus under soil warming that was sustained over six years and was not caused by an extended growing period in early summer. In contrast, E. hermaphroditum only showed a positive shoot growth response to warming in 2011 (+21%), and V. gaultherioides showed no significant growth response. Our results indicate that V. myrtillus might have a competitive advantage over the less responsive co-occurring dwarf shrub species under future global warming.

Non-equilibrium in Alpine Plant Assemblages: Shifts in Europe’s Summit Floras

“…in the Pyrenees and the Alps, is hence likely to change vegetation again, but in combination with climate change it is unlikely that vegetation will change back to its previous composition. Elevated atmospheric CO 2 concentrations did not enhance plant growth in alpine grasslands (Inauen et al 2012;Korner et al 1997) but in shrub communities at treeline (Anadon-Rosell et al 2014;Dawes et al 2013Dawes et al , 2014 where the bilberry (Vaccinium myrtillus) showed more growth, possibly at the cost of smaller or less responsive plant species.…”

The snow and the willows: earlier spring snowmelt reduces performance in the low‐lying alpine shrub Salix herbacea

“…; Anadon‐Rosell et al . ), the responses of prostrate shrubs, particularly deciduous species, to warming and snowmelt change have been relatively understudied (but see Clemmensen & Michelsen ; Kudo et al . ), and rarely so for both factors in combination.…”

The fate of nitrogen inputs in a warmer alpine treeline ecosystem: a 15N labelling study

“…For the Vaccinium species, the amount of N per leaf increased during the first 2 weeks after labelling, during leaf expansion (Anadon‐Rosell et al . ), and then decreased slightly from 2 to 7 weeks ( V. gaultherioides : F 1,54 = 6·98, P = 0·011; V. myrtillus : F 1,62 = 4·31, P = 0·042; Fig. g,h).…”

“…Shoot expansion of this species started in the season and was >80% complete at 4 weeks after label application (Anadon‐Rosell et al . ).…”

“…By 2 weeks after label application, leaves of both species were fully expanded (Anadon‐Rosell et al . ) and new shoots were >80% of their final length (A. Anadon‐Rosell, unpublished data). Vaccinium myrtillus leaves were additionally sampled 2 h after label application; these samples did not show a detectable 15 N signal, indicating that there was negligible direct foliar uptake of the label by vascular plants, at least by this species.…”