Snowmelt Timing Regulates Community Composition, Phenology, and Physiological Performance of Alpine Plants

Abstract

The spatial patterning of alpine plant communities is strongly influenced by the variation in physical factors such as temperature and moisture, which are strongly affected by snow depth and snowmelt patterns. Earlier snowmelt timing and greater soil-moisture limitations may favor wide-ranging species adapted to a broader set of ecohydrological conditions than alpine-restricted species. We asked how plant community composition, phenology, plant water relations, and photosynthetic gas exchange of alpine-restricted and wide-ranging species differ in their responses to a ca. 40-day snowmelt gradient in the Colorado Rocky Mountains (Lewisia pygmaea, Sibbaldia procumbens, and Hymenoxys grandiflora were alpine-restricted and Artemisia scopulorum, Carex rupestris, and Geum rossii were wide-ranging species). As hypothesized, species richness and foliar cover increased with earlier snowmelt, due to a greater abundance of wide-ranging species present in earlier melting plots. Flowering initiation occurred earlier with earlier snowmelt for 12 out of 19 species analyzed, while flowering duration was shortened with later snowmelt for six species (all but one were wide-ranging species). We observed >50% declines in net photosynthesis from July to September as soil moisture and plant water potentials declined. Early-season stomatal conductance was higher in wide-ranging species, indicating a more competitive strategy for water acquisition when soil moisture is high. Even so, there were no associated differences in photosynthesis or transpiration, suggesting no strong differences between these groups in physiology. Our findings reveal that plant species with different ranges (alpine-restricted vs. wide-ranging) could have differential phenological and physiological responses to snowmelt timing and associated soil moisture dry-down, and that alpine-restricted species’ performance is more sensitive to snowmelt. As a result, alpine-restricted species may serve as better indicator species than their wide-ranging heterospecifics. Overall, alpine community composition and peak % cover are strongly structured by spatio-temporal patterns in snowmelt timing. Thus, near-term, community-wide changes (or variation) in phenology and physiology in response to shifts in snowmelt timing or rates of soil dry down are likely to be contingent on the legacy of past climate on community structure.

Warming acts through earlier snowmelt to advance but not extend alpine community flowering

“…The direct effect of heating shortened cushion and succulent flowering duration suggesting these groups may be less able to take advantage of climatic warming and are more at risk for reduced reproductive success than forbs and graminoids (Petanidou et al 2014). This could compound cushion species’ declines in productivity with warming, as detected in the same experiment (Winkler et al 2016), putting this archetypal alpine life‐form at risk of population contraction. Finally, moisture availability most strongly affected date of first and last flower for cushion species, indicating that dry soils would most significantly advance cushion flowering phenology (Fig.…”

“…High wind speeds (mean 5.8 m/s during the snow‐free season; Kueppers et al 2017) diminished heating efficiency relative to that under low wind conditions (Kimball et al 2007) and limited overall warming effects to an average of +1.5 ° C at 5–10 cm depth in the soil during the snow‐free season. Winkler et al (2016) describes the heating treatment in more detail. Infrared radiation (IR) is primarily absorbed by surfaces so our aim was to increase growing season plant and soil temperatures and not to modify air temperature.…”

Variations in ramet performance and the dynamics of an alpine evergreen herb,Gentiana nipponica, in different snowmelt conditions

“…These heterogeneous selective forces may promote local adaptation of the life-history traits among neighboring populations of alpine plants. At the same time, rapid modification of snowmelt conditions by global warming should disturb the inherent ecological situations of local habitats (e.g., Winkler et al, 2018). The predicting plant responses to these climatic changes, such as earlier snowmelt or later onset of winter, may be different between early and late snowmelt populations.…”

Increasing phylogenetic stochasticity at high elevations on summits across a remote North American wilderness

“…We sampled in the months of July and August to capture peak phenology. Phenology in high alpine communities is regulated by environmental cues such as snow melt (Winkler et al., ), and for the most part is coordinated across species due to the short growing season. Specimens were pressed in the field, and leaf tissues were preserved in silica for molecular analyses.…”