Advanced Snowmelt Research Articles

Phenological responses of alpine snowbed communities to advancing snowmelt.

Climate change is leading to advanced snowmelt date in alpine regions. Consequently, alpine plant species and ecosystems experience substantial changes due to prolonged phenological seasons, while the responses, mechanisms and implications remain widely unclear. In this 3-year study, we investigated the effects of advancing snowmelt on the phenology of alpine snowbed species. We related microclimatic drivers to species and ecosystem phenology using in situ monitoring and phenocams. We further used predictive modelling to determine whether early snowmelt sites could be used as sentinels for future conditions. Temperature during the snow-free period primarily influenced flowering phenology, followed by snowmelt timing. Salix herbacea and Gnaphalium supinum showed the most opportunistic phenology, while annual Euphrasia minima struggled to complete its phenology in short growing seasons. Phenological responses varied more between years than sites, indicating potential local long-term adaptations and suggesting these species' potential to track future earlier melting dates. Phenocams captured ecosystem-level phenology (start, peak and end of phenological season) but failed to explain species-level variance. Our findings highlight species-specific responses to advancing snowmelt, with snowbed species responding highly opportunistically to changes in snowmelt timings while following species-specific developmental programs. While species from surrounding grasslands may benefit from extended growing seasons, snowbed species may become outcompeted due to internal-clock-driven, non-opportunistic senescence, despite displaying a high level of phenological plasticity.

Modelling postfire recovery of snow albedo and forest structure to understand drivers of decades of reduced snow water storage and advanced snowmelt timing

AbstractForest fires darken snow albedo and degrade forest structure, ultimately reducing peak snow–water storage, and advancing snowmelt timing for up to 15 years following fire. To date, no volumetric estimates of watershed‐scale postfire effects on snow–water storage and snowmelt timing have been quantified over decades of postfire recovery. Using postfire parameterizations in a spatially‐distributed snow mass and energy balance model, SnowModel, we estimated postfire recovery of forest fire effects on snow–water equivalent (SWE) and snowmelt timing over decades following fire. Using this model, we quantified volumetric recovery of forest fire effects on snow hydrology across a chronosequence of eight sub‐alpine forests burned between 2000 and 2019 in the Triple Divide of western Wyoming. We found that immediately following fire, forest fire effects reduced snow–water storage by 6.8% (SD = 11.2%) and advanced the snow disappearance date by 31 days (SD = 9 days). Across the 15‐year recovery following fire, forest fire effects reduced snow–water storage by 4.5% (SD = 11.4%). Postfire effects on snow hydrology generally recovered over time, but still persisted beyond 15‐years following fire due to the observed postfire shift from forest to open meadow. Estimates of postfire reductions on peak SWE summed over the entire 15‐year postfire recovery period were 18 times greater than the immediate losses in the first winter following fire alone. These lasting effects of forest fires on snow hydrology decades following fire highlight the importance of postfire parameterizations for more accurate watershed‐scale volumetric estimates of forest fire effects on snow–water resources.

Effects of climate change on plant-pollinator interactions and its multitrophic consequences

AbstractThere is wide consensus that climate change will seriously impact flowering plants and their pollinators. Shifts in flowering phenology and insect emergence as well as changes in the functional traits involved can cause alterations in plant-pollinator interactions, pollination success and plant reproductive output. Effects of rising temperatures, advanced snowmelt and altered precipitation patterns are expected to be particularly severe in alpine habitats due to the constrained season and upper range margins. Yet, our understanding of the magnitude and consequences of such changes in life history events and functional diversity in high elevation environments is incomplete.This special issue collects novel insights into the effects of climate change on plant-pollinator interactions in individual plant species and on network structure of entire plant and pollinator communities in alpine ecosystems. Using simulated changes of earlier snowmelt, natural gradients of variation in temperature, precipitation and snowmelt, or a long-term monitoring approach, these studies illustrate how plant species, plant communities, and pollinators respond to variation in environmental conditions associated with scenarios of ongoing climate change.The collection of papers presented here clearly demonstrates how spatial or temporal variation in the environmental climatic context affects flower abundances and plant community composition, and the consequences of these changes for pollinator visitation, pollination network structure, pollen transfer dynamics, or seed production. As changes in the availability of flowers, fruits, and seeds are likely to impact on other trophic levels, the time is ripe and pressing for a holistic multitrophic view of the effects of climate change on biotic interactions in alpine ecological communities.

Early snowmelt advances flowering phenology and disrupts the drivers of pollinator visitation in an alpine ecosystem

AbstractClimate change is altering interactions among plants and pollinators. In alpine ecosystems, where snowmelt timing is a key driver of phenology, earlier snowmelt may generate shifts in plant and pollinator phenology that vary across the landscape, potentially disrupting interactions. Here we ask how experimental advancement of snowmelt timing in a topographically heterogeneous alpine-subalpine landscape impacts flowering, insect pollinator visitation, and pathways connecting key predictors of plant-pollinator interaction. Snowmelt was advanced by an average of 13.5 days in three sites via the application of black sand over snow in manipulated plots, which were paired with control plots. For each forb species, we documented flowering onset and counted flowers throughout the season. We also performed pollinator observations to measure visitation rates. The majority (79.3%) of flower visits were made by dipteran insects. We found that plants flowered earlier in advanced snowmelt plots, with the largest advances in later-flowering species, but flowering duration and visitation rate did not differ between advanced snowmelt and control plots. Using piecewise structural equation models, we assessed the interactive effects of topography on snowmelt timing, flowering phenology, floral abundance, and pollinator visitation. We found that these factors interacted to predict visitation rate in control plots. However, in plots with experimentally advanced snowmelt, none of these predictors explained a significant amount of variation in visitation rate, indicating that different predictors are needed to understand the processes that directly influence pollinator visitation to flowers under future climate conditions. Our findings demonstrate that climate change-induced early snowmelt may fundamentally disrupt the predictive relationships among abiotic and biotic drivers of plant-pollinator interactions in subalpine-alpine environments.

Black carbon and dust alter the response of mountain snow cover under climate change

By darkening the snow surface, mineral dust and black carbon (BC) deposition enhances snowmelt and triggers numerous feedbacks. Assessments of their long-term impact at the regional scale are still largely missing despite the environmental and socio-economic implications of snow cover changes. Here we show, using numerical simulations, that dust and BC deposition advanced snowmelt by 17 ± 6 days on average in the French Alps and the Pyrenees over the 1979–2018 period. BC and dust also advanced by 10-15 days the peak melt water runoff, a substantial effect on the timing of water resources availability. We also demonstrate that the decrease in BC deposition since the 1980s moderates the impact of current warming on snow cover decline. Hence, accounting for changes in light-absorbing particles deposition is required to improve the accuracy of snow cover reanalyses and climate projections, that are crucial for better understanding the past and future evolution of mountain social-ecological systems.

Early snowmelt by an extreme warming event affects understory more than overstory trees in Japanese temperate forests

AbstractThe occurrence of extreme warm events and early snowmelt is predicted to increase in high‐latitude ecosystems, even during periods of time when there is no coincident reduction in total precipitation. However, because extreme events like these occur unpredictably, little is known about how advancing snowmelt by a single extreme warm event, without a reduction in precipitation amount, influences overstory trees and understory vegetation simultaneously in an ecosystem. We conducted a warming experiment (four 20 × 20 m plots) in temperate forests of Japan to determine the effects of earlier snowmelt on both understory dwarf bamboo plants and overstory birch trees. Our experimental treatment advanced snowmelt by about 10 days and increased soil temperatures that were associated with increased rates of soil nitrogen (N) mineralization and nitrification. Furthermore, these changes led to lower C:N ratios of leaves together with the greater growth of understory bamboo vegetation, with no changes in leaf C:N or growth rates of overstory birch trees. Together, our results demonstrate that advancing snowmelt by an extreme warm event in temperate forests is likely to affect N cycling and will benefit understory vegetation without a commensurate change in overstory vegetation, likely due to the increase in available soil N. These results also demonstrate that with the projected increase in the frequency of extreme warm events and advanced snowmelt, understory vegetation is likely to benefit more than overstory trees in Japanese temperate forests with heavy snow.

From the ground up: Building predictions for how climate change will affect belowground mutualisms, floral traits, and bee behavior

Climate change affects species and their interactions, resulting in novel communities and modified ecosystem processes. Through shifts in phenology and distribution, climatic change can disrupt interactions, including those between mutualists. Mutualisms influence the structure and stability of communities and can link species to a common fate. However, research on climate change has focused on pairwise mutualisms, neglecting the higher-order interactions that can arise when species interact with multiple mutualists. We explore the effects of climate change on tripartite interactions involving belowground mutualists, namely soil bacteria and fungi, flowering plants, and pollinators. We outline how climate change is predicted to affect the phenology and distribution of these belowground mutualists, emphasizing the consequent effects on host plant floral traits, plant-pollinator interactions, and bee behavior. We find evidence that warming, advanced snowmelt, and drought are likely to cause phenological and distributional shifts in soil microbes, leading to diminished mutualistic interactions with plants and symbiont switching. Consequently, shifts in flowering phenology, smaller floral displays, and lower quality floral rewards are expected, increasing foraging time and energy demands for bees and altering their floral preferences. Such costs could translate into reduced fitness and novel selection pressures for bees and flowering plants in the short term. We highlight knowledge gaps and ways forward, urging studies on microbe dispersal and phenological cues, experiments that manipulate soil microbe-host plant interactions under simulated climate change conditions, and large-scale field studies across environmental gradients, all with the goal of understanding how climate change will affect soil microbe-plant-pollinator mutualisms.

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

Large-scale warming will alter multiple local climate factors in alpine tundra, yet very few experimental studies examine the combined yet distinct influences of earlier snowmelt, higher temperatures and altered soil moisture on alpine ecosystems. This limits our ability to predict responses to climate change by plant species and communities. To address this gap, we used infrared heaters and manual watering in a fully factorial experiment to determine the relative importance of these climate factors on plant flowering phenology, and response differences among plant functional groups. Heating advanced snowmelt and flower initiation, but exposed plants to colder early-spring conditions in the period prior to first flower, indicating that snowmelt timing, not temperature, advances flowering initiation in the alpine community. Flowering duration was largely conserved; heating did not extend average species flowering into the latter part of the growing season but instead flowering was completed earlier in heated plots. Although passive warming experiments have resulted in warming-induced soil drying suggested to advance flower senescence, supplemental water did not counteract the average species advance in flowering senescence caused by heating or extend flowering in unheated plots, and variation in soil moisture had inconsistent effects on flowering periods. Functional groups differed in sensitivity to earlier snowmelt, with flower initiation most advanced for early-season species and flowering duration lengthened only for graminoids and forbs. We conclude that earlier snowmelt, driven by increased radiative heating, is the most important factor altering alpine flowering phenology. Studies that only manipulate summer temperature will err in estimating the sensitivity of alpine flowering phenology to large-scale warming. The wholesale advance in flowering phenology with earlier snowmelt suggests that alpine communities will track warming, but only alpine forbs and graminoids appear able to take advantage of an extended snow-free season.

Accelerated Snowmelt Protocol to Simulate Climate Change Induced Impacts on Snowpack Dependent Ecosystems.

Field studies that simulate the effects of climate change are important for a predictive understanding of ecosystem responses to a changing environment. Among many concerns, regional warming can result in advanced timing of spring snowmelt in snowpack dependent ecosystems, which could lead to longer snow-free periods and drier summer soils. Past studies investigating these impacts of climate change have manipulated snowmelt with a variety of techniques that include manual snowpack alteration with a shovel, infrared radiation, black sand and fabric covers. Within these studies however, sufficient documentation of methods is limited, which can make experimental reproduction difficult. Here, we outline a detailed plot-scale protocol that utilizes a permeable black geotextile fabric deployed on top of an isothermal spring snowpack to induce advanced snowmelt. The method offers a reliable and cost-effective approach to induce snowmelt by passively increasing solar radiation absorption at the snow surface. In addition, control configurations with no snowpack manipulation are paired adjacent to the induced snowmelt plot for experimental comparison. Past and ongoing deployments in Colorado subalpine ecosystems indicate that this approach can accelerate snowmelt by 14-23 days, effectively mimicking snowmelt timing at lower elevations. This protocol can be applied to a variety of studies to understand the hydrological, ecological, and geochemical impacts of regional warming in snowpack dependent ecosystems.

Intraspecific Functional Trait Response to Advanced Snowmelt Suggests Increase of Growth Potential but Decrease of Seed Production in Snowbed Plant Species.

In ecological theory, it is currently unclear if intraspecific trait responses to environmental variation are shared across plant species. We use one of the strongest environmental variations in alpine ecosystems, i.e., advanced snowmelt due to climate warming, to answer this question for alpine snowbed plants. Snowbeds are extreme habitats where long-lasting snow cover represents the key environmental factor affecting plant life. Intraspecific variation in plant functional traits is a key to understanding the performance and vulnerability of species in a rapidly changing environment. We sampled snowbed species after an above-average warm winter to assess their phenotypic adjustment to advanced snowmelt, based on differences in the natural snowmelt dynamics with magnitudes reflecting predicted future warming. We measured nine functional traits related to plant growth and reproduction in seven vascular species, comparing snowbeds of early and late snowmelt across four snowbed sites in the southern Alps in Italy. The early snowbeds provide a proxy for the advanced snowmelt caused by climatic warming. Seed production was reduced under advanced snowmelt in all seed-forming snowbed species. Higher specific leaf area (SLA) and lower leaf dry matter content (LDMC) were indicative of improved growth potential in most seed-forming species under advanced snowmelt. We conclude, first, that in the short term, advanced snowmelt can improve snowbed species’ growth potential. However, in the long term, results from other studies hint at increasing competition in case of ongoing improvement of conditions for plant growth under continued future climate warming, representing a risk for snowbed species. Second, a lower seed production can negatively affect the seed rain. A reduction of propagule pressure can be crucial in a context of loss of the present snowbed sites and the formation of new ones at higher altitudes along with climate warming. Finally, our findings encourage using plant functional traits at the intraspecific level across species as a tool to understand the future ecological challenges of plants in changing environments.

Projections of water, carbon, and nitrogen dynamics under future climate change in an alpine tundra ecosystem in the southern Rocky Mountains using a biogeochemical model

Using statistically downscaled future climate scenarios and a version of the biogeochemical model (PnET-BGC) that was modified for use in the alpine tundra, we investigated changes in water, carbon, and nitrogen dynamics under the Representative Concentration Pathways at Niwot Ridge in Colorado, USA. Our simulations indicate that future hydrology will become more water-limited over the short-term due to the temperature-induced increases in leaf conductance, but remains energy-limited over the longer term because of anticipated future decreases in leaf area and increases in annual precipitation. The seasonal distribution of the water supply will become decoupled from energy inputs due to advanced snowmelt, causing soil moisture stress to plants during the growing season. Decreases in summer soil moisture are projected to not only affect leaf production, but also reduce decomposition of soil organic matter in summer despite increasing temperature. Advanced future snowmelt in spring and increasing rain to snow ratio in fall are projected to increase soil moisture and decomposition of soil organic matter. The extended growing season is projected to increase carbon sequestration by 2% under the high radiative forcing scenario, despite a 31% reduction in leaf display due to the soil moisture stress. Our analyses demonstrate that future nitrogen uptake by alpine plants is regulated by nitrogen supply from mineralization, but plant nitrogen demand may also affect plant uptake under the warmer scenario. PnET-BGC simulations also suggest that potential CO2 effects on alpine plants are projected to cause larger increases in plant carbon storage than leaf and root production.

Micro-climatic controls and warming effects on flowering time in alpine snowbeds.

Alpine snowbed communities are among the habitats most threatened by climate change. The warmer temperature predicted, coupled with advanced snowmelt time, will influence flowering phenology, which is a key process in species adaptation to changing environmental conditions and plant population dynamics. However, we know little about the effects of changing micro-climate on flowering time in snowbeds and the mechanisms underlying such phenological responses. The flowering phenology of species inhabiting alpine snowbeds was assessed with weekly observations over five growing seasons. We analysed flowering time in relation to micro-climatic variation in snowmelt date, soil and air temperature, and experimental warming during the snow-free period. This approach allowed us to test hypotheses concerning the processes driving flowering phenology. The plants were finely tuned with inter-annual and intra-seasonal variations of their micro-climate, but species did not track the same micro-climatic feature to flower. At the growing-season time-scale, the air surrounding the plants was the most common trigger of the blooming period. However, at the annual time-scale, the snowmelt date was the main controlling factor for flowering time, even in warmer climate. Moreover, spatial patterns of the snowmelt influenced the developmental rate of the species because in later snowmelt sites the plants needed a lower level of heat accumulation to enter anthesis. Phenological responses to experimental warming differed among species, were proportional to the pre-flowering time-span of plants, and did not show consistent trends of change over time. Finally, warmer temperature produced an overall increase of flowering synchrony both within and among plant species.

Soil moisture mediates alpine life form and community productivity responses to warming.

Climate change is expected to alter primary production and community composition in alpine ecosystems, but the direction and magnitude of change is debated. Warmer, wetter growing seasons may increase productivity; however, in the absence of additional precipitation, increased temperatures may decrease soil moisture, thereby diminishing any positive effect of warming. Since plant species show individual responses to environmental change, responses may depend on community composition and vary across life form or functional groups. We warmed an alpine plant community at Niwot Ridge, Colorado continuously for four years to test whether warming increases or decreases productivity of life form groups and the whole community. We provided supplemental water to a subset of plots to alleviate the drying effect of warming. We measured annual above-ground productivity and soil temperature and moisture, from which we calculated soil degree days and adequate soil moisture days. Using an information-theoretic approach, we observed that positive productivity responses to warming at the community level occur only when warming is combined with supplemental watering; otherwise we observed decreased productivity. Watering also increased community productivity in the absence of warming. Forbs accounted for the majority of the productivity at the site and drove the contingent community response to warming, while cushions drove the generally positive response to watering and graminoids muted the community response. Warming advanced snowmelt and increased soil degree days, while watering increased adequate soil moisture days. Heated and watered plots had more adequate soil moisture days than heated plots. Overall, measured changes in soil temperature and moisture in response to treatments were consistent with expected productivity responses. We found that available soil moisture largely determines the responses of this forb-dominated alpine community to simulated climate warming.

Interactive effects of elevation, species richness and extreme climatic events on plant-pollinator networks.

Plant-pollinator interactions are essential for the functioning of terrestrial ecosystems, but are increasingly affected by global change. The risks to such mutualistic interactions from increasing temperature and more frequent extreme climatic events such as drought or advanced snow melt are assumed to depend on network specialization, species richness, local climate and associated parameters such as the amplitude of extreme events. Even though elevational gradients provide valuable model systems for climate change and are accompanied by changes in species richness, responses of plant-pollinator networks to climatic extreme events under different environmental and biotic conditions are currently unknown. Here, we show that elevational climatic gradients, species richness and experimentally simulated extreme events interactively change the structure of mutualistic networks in alpine grasslands. We found that the degree of specialization in plant-pollinator networks (H2') decreased with elevation. Nonetheless, network specialization increased after advanced snow melt at high elevations, whereas changes in network specialization after drought were most pronounced at sites with low species richness. Thus, changes in network specialization after extreme climatic events depended on climatic context and were buffered by high species richness. In our experiment, only generalized plant-pollinator networks changed in their degree of specialization after climatic extreme events. This indicates that contrary to our assumptions, network generalization may not always foster stability of mutualistic interaction networks.

Combined effects of warming, snowmelt timing, and soil disturbance on vegetative development in a grassland community

Climate warming and advanced snowmelt can simultaneously affect plant communities. However, the process of seasonal vegetative development under warming and early snowmelt conditions remains unclear, especially given that disturbance can amplify or dampen the effect of warming. This study addressed these issues using a 3-year experiment in a productive grassland in a cool temperate region. Three experimental conditions were established in the grassland: warming and early snowmelt using open-top chambers (OTCs), early snow removal and ambient temperature (SRs), and natural snowmelt and ambient temperature (CONTs). Half of the area of all plots was plowed to disturb soil conditions. Average temperature and snowmelt were 1.37 °C higher and 16–26 days earlier in OTCs relative to CONTs, respectively. Vegetation censuses during the 1–4 week intervals showed earlier increases in species richness and vegetation cover after snowmelt in OTCs than CONTs and SRs. Differences in species richness and plant cover among treatments were substantially diminished in plowed areas. Aboveground biomass showed little difference among treatments at the end of the growing season, while richness remained higher in OTCs. These results indicate that early snow removal did not alter grassland vegetation. The effect of OTCs can thus be due to either warming or a combination of early snowmelt and warming. Although climate change is predicted to have strong impacts on arctic and alpine ecosystems, this study suggests that the warming may also have important impacts in temperate regions.

Responses of flowering phenology of snowbed plants to an experimentally imposed extreme advanced snowmelt

In snowbed habitats, characterized by a long-lasting snow cover, the timing of snowmelt can be included among the major factors controlling plant phenology. Nevertheless, only a few ecological studies have tested the responses of flowering phenology of species growing in very late snow-free habitats to an advanced snowmelt (AS) date. The aim of this study was to determine the impacts of an extremely earlier melt-out of snow on flowering phenology of vascular plant species inhabiting an alpine snowbed. The study was conducted in the high Gavia Valley (Italy, 2,700 m a.s.l.). On 30th May 2012, we removed manually the snow cover and set up an experiment with 5 AS and 5 control plots. Phenological observations of the most abundant vascular species were conducted every 4–6 days. Moreover, we calculated cumulative soil temperature and recorded the mortality of reproductive structures of three species. For several species flowering occurred earlier, and the prefloration period was extended in the AS treatment in comparison with the control. For the majority of species, cumulative soil temperatures in the AS treatment and the control were comparable, confirming that temperature exerts the main control on the flowering of the species inhabiting snowbeds. Earlier flowering species resulted more affected by an AS date in comparison with later flowering species. The mortality of reproductive structures did not increase in the AS treatments in comparison with the control suggesting that few and weak frost events in late spring do not affect the survival of reproductive structures of the species studied.

Changes in ant community composition caused by 20 years of experimental warming vs. 13 years of natural climate shift

Predicting the effects of climate change on community composition is hampered by the lack of integration between long term data sets tracking the effects of natural climate change and the results of experimental climate manipulations. Here we compare the effects of change in climate through time to experimental warming on the composition of high elevation ant communities at the Rocky Mountain Biological Station in Gothic Colorado. We take advantage of a 20‐year continuously running warming experiment which has increased soil temperature by 1.5°C and advanced snowmelt by 10 days and compare the effects of this experimental warming to natural changes in climate over the past 13 years across three sites spread along a 420‐m elevation gradient representing a roughly 1°C difference in average annual soil temperature and average advanced snowmelt of 2 weeks. We compared ant community data collected at all four sites in 1997 to collections made at the same sites in 2010. From 1997 to 2010 there was a community wide shift in ant composition along the natural climate gradient with ant communities shifting to higher elevations. Ant communities in the experimental warming site also changed, but they shifted orthogonally to those along the gradient. Interestingly, after 20 years of experimental warming, there is little discernible effect on ant communities in experimentally warmed plots compared to control plots. This discrepancy between the climate manipulation and elevation gradient is probably an effect of the spatial scale of the experimental warming. Ants respond to experimental warming in complex ways due to the physical location of their nests and their foraging area. This is a concern for warming experiments, but one that is hard to address for species that cover even modest areas in their foraging.

Warming effects and plant trait control on the early-decomposition in alpine snowbeds

Background and aims In cold biomes, litter decomposition, which controls the nutrient availability for plants and the ecosystem carbon budget, is strongly influenced by climatic conditions. In this study, focused on the early litter decay within snowbed habitats, the magnitude of the short- and long-term influences of climate warming, the direction of the effects of warmer temperature and advanced snowmelt, and the control of microclimatic features and plant traits were compared.

Phenological response of grassland species to manipulative snowmelt and drought along an altitudinal gradient.

Plant communities in the European Alps are assumed to be highly affected by climate change, as the temperature rise in this region is above the global average. It is predicted that higher temperatures will lead to advanced snowmelt dates and that the number of extreme weather events will increase. The aims of this study were to determine the impacts of extreme climatic events on flower phenology and to assess whether those impacts differed between lower and higher altitudes. In 2010, an experiment simulating advanced and delayed snowmelt as well as a drought event was conducted along an altitudinal transect approximately every 250 m (600–2000 m above sea level) in the Berchtesgaden National Park, Germany. The study showed that flower phenology was strongly affected by altitude; however, there were few effects of the manipulative treatments on flowering. The effects of advanced snowmelt were significantly greater at higher than at lower sites, but no significant difference was found between both altitudinal bands for the other treatments. The response of flower phenology to temperature declined through the season and the length of flowering duration was not significantly influenced by treatments. The stronger effect of advanced snowmelt at higher altitudes may be a response to differences in treatment intensity across the gradient. Consequently, shifts in the date of snowmelt due to global warming may affect species more at higher than at lower altitudes, as changes may be more pronounced at higher altitudes. These data indicate a rather low risk of drought events on flowering phenology in the Bavarian Alps.

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

AbstractQuestionIn 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.LocationA sub‐alpine heath in the Northern Apennines (Italy).MethodsWe 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 (2004–2006), with a mean delay in snowmelt timing of about 2 wk from −S to +S. In a companion experiment, we simulated a freezing event in late spring 2004.ResultsDuring the snowmelt period, the −S plants experienced 6–10 more frost events, compared with +S and unmanipulated controls (C) in 2004 and 2005, but not in 2006. In the first 2 yr 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.ConclusionsThe results overall support our hypothesis, as shown by the differing effects of snow depth and timing of melt on V. myrtillus in the 3 yr. 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.