ID61: Snow cover change and mountain ecology

Abstract ID 714 | Date: 2022-09-13 10:11 – 10:22 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Hammerle, Albin (1); Tasser, Erich (1,2); Matiu, Michael (3); Wohlfahrt, Georg (1)

The Alps are experiencing large climatic and socio-economic changes. Climate change is leading to an above-average increase in temperatures and subsequent changes in the timing and duration of snow cover. In parallel, socio-economic changes are affecting land use in the Alpine region. Both, snow cover duration/timing and land use changes directly affect the surface albedo of this landscape and therefore the energy balance of this region. Globally, changes in surface albedo due to land use changes and changes in snow/ice cover affect surface albedo, and thus radiative forcing, in opposite directions.

In this study, we investigated the impact of five different future land use scenarios, 12 future snow cover scenarios on the surface albedo in the alpine region of South Tyrol (Italy) in the year 2100 compared to conditions in 2010. Both, the individual effects of changes in land use and future snow cover patterns were investigated, as well as the interactive effects of these two processes.

The hypothetical changes in albedo until 2100 associated with changes in land and/or snow cover were assessed by establishing a surface albedo model based on remotely sensed albedo (MODIS MCD43A1), snow cover data (MODIS MOD10A1), land cover data, as well as geographical information (ASTER ASTGTM). Four potential future land covers were developed on the basis of likely socio-economic pathways as well as one hypothetical scenario and their spatial distribution was mapped. Snow cover scenarios for 2100 are based on EURO CORDEX RCP 2.6 and 8.5 climate scenarios.

Snow cover was by far the most important predictor for albedo, followed by the occurrence of needle leaf forests using a regression tree algorithm, which exhibited excellent skill in modelling current albedo conditions based on the above-mentioned predictors.

All likely future land cover scenarios caused similar increases in spatially averaged albedo of the study domain, while likely future snow cover conditions lead to a decrease in average albedo, the magnitude of which depended on the chosen RCP and combination of global/regional climate model. Simulations with factorial combinations of land cover and snow cover scenarios somewhat moderated the decrease in albedo caused by the snow cover changes, but in no case likely land cover changes compensated for the albedo decrease caused by snow cover changes. Only the hypothetical, unrealistic scenario with a dramatic decrease in forest areas increased the average albedo.

Abstract ID 909 | Date: 2022-09-13 10:22 – 10:33 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Navarro, Carlos Javier (1); Martínez-López, Javier (1); Postma, Thedmer M. (1); Castro, Jorge (2); Leverkus, Alexandro B. (2); Alcaraz-Segura, Domingo (3)

Managing forests after wildfire involves modifying, and often removing, large amounts of biological legacies in the form of burnt wood. This may, in turn, affect different ecosystem processes and functions and ultimately determine the speed of regeneration of biodiversity and ecosystem services. The effect of postfire management on the hydrological cycle –particularly on those processes related to snow cover– has been little studied so far. In this study, we assessed the effect of salvage logging, partial logging and no intervention after a wildfire on the duration and abundance of the snow cover in the Sierra Nevada protected area (Spain). We used 20 years of Landsat images of the Normalized Difference Snow Index (NDSI) to characterize the temporal dynamics (seasonal and interannual) of snow cover in several experimental plots before and after a wildfire event in 2005. Within each treatment and plot, Landsat pixels (~30 m) were first categorized into homogeneous classes that could be analyzed independently, through visual interpretation of historical orthophotos, based on the percentage of burned area and tree cover. Pixels from each treatment and plot were further selected to exclude the effect of standing living trees, the presence of gullies and bare rock, and to account for mixed-treatment pixels. Images were corrected for cloud cover and an NDSI threshold was established to map snow cover by comparing it with a MODIS snow product. Preliminary results showed that active wood management after wildfire seems to have a negative effect on snow duration and quantity compared with no intervention, at least during the first years. Longer duration of the snow cover can have positive feedback on forest regeneration in high mountains by protecting the seedbank from extreme cold temperatures, by increasing soil humidity, and by extending the period of snow melt and consequent water availability into the spring.

Abstract ID 385 | Date: 2022-09-13 10:33 – 10:44 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Ganthaler, Andrea (1); Charra-Vaskou, Katline (1,2); Ameglio, Thierry (2); Charrier, Guillaume (2); Mayr, Stefan (1)

Climate change is expected to affect snow cover dynamics at high elevation sites, leading to changes in both height and duration of the snow cover. While earlier snow melt and later snow fall may affect positively the length of the growing season, plants would also be less protected from climatic extremes, and suffer more severe winter drought and frost stress. In woody species, such as shrubs and trees at the alpine treeline, reduced snow cover may lead (besides drought due to transpirational losses) to more frequent freeze-thaw cycles in the plant xylem, and thereby affect living and dead xylem cells and impair their hydraulic function. Freeze-thaw cycles can induce the formation of embolism that block water transport in the conduits and thus impair the water supply of distal tissues. Plants must cope with such hydraulic limitation by repair of dysfunctional xylem or formation of new xylem tissue, which in turn can be impeded by frost-induced damages on living cells.

To better understand freeze-thaw-induce embolism, how plants overcome xylem dysfunction, and the potential trade-offs with plant growth and survival, five contrasting woody species are studied in the project “AcouFollow” by a snow-manipulation experiment at a high elevation field site in Tyrol (Austria). Species were selected according to their leaf phenology (evergreen/deciduous), growth form (shrub/tree) and wood anatomy (vesselless/diffuse porous) and include Juniperus communis, Larix decidua, Picea abies, Acer pseudoplatanus, and Sorbus aucuparia. Young trees were monitored under limited and extended snow cover duration through high resolution dendrometer measurements, ultrasonic acoustic emission analysis, and various complementary parameters (e.g., leaf phenology, soil and xylem temperature, water potential, and hydraulics).

Monitoring and snow manipulation approaches are expected to unravel the complex spatio-temporal dynamics of embolism formation during freeze-thaw cycles under varying snow depth situations and the potential for embolism repair under highly constrained environmental conditions. We hypothesize that the duration and height of snow cover influences both winter damages and recovery and that snow removal has overall negative impacts on plant hydraulics and growth. Species-specific differences in vulnerability to freeze-thaw-induced embolism and the potential for recovery will be discussed in the context of growth form, wood anatomical traits, and leaf phenology. Results will contribute to an improved knowledge of freezing tolerance and resilience of high mountain woody species and to enable projections of xylem dysfunction risks under future climatic and snow cover conditions.

Abstract ID 728 | Date: 2022-09-13 10:44 – 10:55 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Crepaz, Harald (1); Niedrist, Georg (1); Rossi, Mattia (2); Tappeiner, Ulrike (1,3)

The impacts of changing climate on alpine vegetation have already been intensively investigated and findings indicate that alpine grasslands will undergo substantial changes, especially due to increasing temperatures and changes in snow dynamics. Snowbeds comprise a complex microclimatic and topographic mosaic and facilitate the growth of species with diverse phytosociological optima and survival strategies. Many snowbed species are highly specialized to short vegetation periods, e.g., through their phenological cycle. Hence, climate change is expected to have a large impact on alpine plant communities and will lead to substantial changes by favoring some species and penalizing others.
To identify those key-species and to assess the effects of increasing temperatures and changing snow-dynamics on snowbed-communities, we set up permanent observation plots in ten snowbeds at two study sites in the Italian Alps (Cimalegna and Mazia), that mainly differ in snow dynamics and growing season length. We monitored the phenological development of six species present for three years by a standard protocol for phenological phases (BBCH) and for one season by an IR/RGB-phenocam. We related the phenological stages to the season- and climate-related variables Day Of Year (DOY), Days From Snow Melt (DFSM), and Thawing Degree Days (TDD) and compared results from the early snowmelt site (Mazia) with those from the late snowmelt site (Cimalegna). We further used Generalized Additive Mixed Models (GAMM) to predict changes in phenology under advancing snowmelt.
Our results indicate that phenological development in general correlated better with TDD and DFSM than with DOY. Furthermore, we found substantial differences in the phenological timing of the species. In 2020, early flowering species like Salix herbacea completed the phenological cycle around DOY 234, while late flowering species like Euphrasia minima took until DOY 260. Also, vegetative indices (green chromatic coordinate GCC, and excess greenness ExG) between the study sites differed considerably due to different cover: GCC at Cimalegna peaked three weeks later than in Mazia, while reaching up to 10% higher values. Furthermore, our models demonstrated good predictive quality simulating the phenological cycles of Salix herbacea and Poa alpina under decreasing snow cover but performed poor for Gnaphalium supinum and Agrostis rupestris. This suggest that some species might be able to adapt to changing climatic conditions better than others, giving them advantage in a warmer future.

Abstract ID 241 | Date: 2022-09-13 10:57 – 11:08 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Apple, Martha Elizabeth (1); Gallagher, James (2); Wincot, Kurtiss (1); Negus, Kevin (1)

Polygonal periglacial patterned ground provides a mosaic of microhabitats. These polygons generally have snowy edges with non-snowy centers and are found on the climate-change sensitive alpine tundra of Goat Flat (2837 m; 46° 3′ 17″ N, 113° 16′ 43″ W) of the Pintler Mountains of Montana. The polygons represent an array of microhabitats with predictive value concerning which plants may live in the alpine tundra with loss or gains of snow.

At Goat Flat, we studied the spatial distribution of plant species and functional traits with respect to position on the edges or centers of the polygons and installed an array of ONSET Hobo TidbitV2 #UTBI-001 soil temperature sensors 5-10 cm beneath the soil surface, with hourly measurements from 2018-2022. We found that plant species and functional traits (which interact with the environment and influence where plants can live) differ with position on the polygons. The sparsely vegetated polygon centers are inhabited by a significantly higher percentage of xeromorphic (drought tolerant), tap rooted, herbaceous plants, with a significantly higher relative percent cover (RPC) of Sedum lanceolatum and Sedum rosea, which both have the drought-tolerant trait of crassulacean acid metabolism (CAM), and a significantly higher RPC of the viviparous Polygonum viviparum. In contrast, the polygon edges were dominated by mat-forming adventitiously rooted dwarf shrubs, including the evergreen Dryas octopetala and the deciduous Salix arctica, also had herbaceous monocots and dicots, and the gymnosperm, Picea engelmannii.

Polygon centers had higher summer temperatures with more variable annual temperatures than the polygon edges. These temperature differences may contribute to patterns of plant functional trait distribution. In addition, we anticipate obtaining soil moisture data from the polygon edges and centers of Goat Flat in the summer of 2022 and onward. Sensor data are valuable in linking environmental conditions with the distribution of life forms on the alpine tundra. Current microhabitats with contrasting snow conditions, soil temperatures, and plant functional trait distributions can be used to predict the distribution of plant species and functional traits with increased or decreased snow.

Abstract ID 564 | Date: 2022-09-13 11:08 – 11:19 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Zong, Shengwei (1); Rixen, Christian (2)

Pronounced climate warming has resulted in a significant reduction of snow cover extent, as well as poleward and upslope shifts of shrubs in Arctic and alpine ecosystems. However, it is difficult to establish links between changes in snow cover and shrub distribution changes due to a lack of in situ and long-term snow records in relation to abundance shifts of shrubs at their leading and trailing edges. We used remote sensing to extract long-term changes in both snow cover and shrub distributions in the alpine tundra of the Changbai Mountains, Northeast China. First, we analyzed spatio-temporal changes in snow cover during the snowmelt period (April 1st to June 15th) over the past 54 years (1965–2019). Then, we analyzed distribution changes of the dominant evergreen alpine shrub, Rhododendron aureum, using 31 years (1988–2019) of Landsat NDVI archives. Finally, we tested the relationship between snowmelt date and the distribution of R. aureum. We found that the fraction cover of R. aureum experienced greater loss than gain in the last 30 years. R. aureum expanded at the leading edge, establishing in snow-rich habitats, yet retracted further at the trailing edge due to loss of snow habitats. We found that further advances in snowmelt dates would lead to the upward range shift of R. aureum in a warming climate. Our study highlights that long-term changes in snow cover due to climate change have already had marked impacts on plant species distributions in alpine ecosystems.

Abstract ID 466 | Date: 2022-09-13 11:19 – 11:30 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Rumpf, Sabine B. (1,2); Gravey, Mathieu (3,4); Brönnimann, Olivier (1,3); Luoto, Miska (5); Cianfrani, Carmen (1); Mariethoz, Gregoire (3); Guisan, Antoine (1,3)

Mountains are hotspots of biodiversity and ecosystem services, but are warming about twice as fast as the global average. Similar warming is observed in the Arctic, resulting in pronounced greening and melting. However, it is unclear whether such large-scale trends are also apparent in mountain environments. Here, we demonstrate that 69% of the European Alps above the tree line experienced greening and only 1% browning over the last four decades. Snow cover declined, albeit to a lesser extent. These trends were only weakly correlated, because greening predominated in warmer areas than melting, i.e., at lower elevations. Greening was mainly driven by warming, while melting was additionally affected by precipitation changes. Even though greening involves carbon sequestration, this is unlikely to outweigh the negative implications of the observed trends, such as reduced albedo and water availability, melting permafrost, and loss of habitats.

Abstract ID 746 | Date: 2022-09-13 11:30 – 11:41 | Type: Oral Presentation | Place: SOWI – Seminar room U1 |

Müller, Svenja (1); Knoflach, Bettina (1); Schulz, Isabella (1); Krappmann, Anna-Viola (1); Stötter, Johann (1); Illmer, Paul (2); Geitner, Clemens (1)

A major consequence of snow cover change for high mountain soils are changing temperature dynamics and all subsequent effects on soil ecology and other soil characteristics. To study the effect of changing snow and frost conditions, we selected 25 study sites along two elevation gradients, the first one being lcated in “Hintere Ölgrube”, the second one in a periglacial and therefore frost-dominated area “Krummgampental” (both Upper Kaunertal, AT).

The elevation gradients ranged from 2300-3000 m a.s.l. and included not only several representative sites for the respective elevation / life zone, but also several sites with distinct frost-related characteristics just meters away (e.g., snow accumulation in snowbed depressions, less snow on hilltops, different slope expositions, patterned ground indicating frost activity such as stone sorting or earth hummocks, …). At every site, at three points, we sampled soil horizons up to 10 cm soil depth, and analysed the samples for soil organic matter, soil pH, soil nutrients, water holding capacity, soil microbial biomass and activity, and root biomass. Also, for a period of 2-3 years, we continuously measured soil temperature and soil water potential at most sites.

Between the sites, we observed strong differences of soil temperature curves throughout the last years, which can be connected to the topographical variety of the sites, which then again causes different snow cover situations during autumn, winter, and springtime.

The differences in soil temperature influenced several soil parameters. For example, sites with less snow cover and colder winter soil temperatures had less microbial activity, less soil nutrients (plant-available nitrogen (NH₄­⁺), dissolved organic carbon), and less root biomass. First results indicate that snow cover in steep slope positions during springtime can also protect areas from springtime erosion, leading to higher soil organic matter contents in both topsoil and subsoil, as well as more root biomass.

We also show an approach of combining today’s soil data with the permafrost history of the sites, using a permafrost model of the current climatic period, as well as of climatic periods since the Little Ice Age.

Abstract ID 152 | Date: 2022-09-13 10:55 – 10:57 | Type: Poster Presentation | Place: SOWI – Seminar room U1 |

Verrall, Brodie (1); Green, Ken (2); Pickering, Catherine (1)

Snowpatches (synonymous with ‘snowbed’) are discrete periglacial ecosystems that occur in topographical depressions on lee aspects of mountain ridgelines where snow amasses throughout the winter. These ecosystems are characterised by short growing seasons as snow persists months after the general thaw, resulting in distinctive and highly specialised plant communities. These communities are threatened by climate change, especially in marginal alpine environments such as Australia where re-surveys have already detected changes in vegetation. Dynamics in snowpatches were further explored through a third survey based on the hypothesis that there would be snowmelt dependant responses to climate change, with increases in competitive generalists and reduction in specialists where snow persists the longest. Seven of the most persistent snowpatches in Australia were categorised into early, mid and late snowmelt zones based on growing season length. Soil temperatures were recorded from winter 2003 to autumn 2020 to assess microclimate dynamics. Plant composition was visually assessed at 84 1 m² quadrats in 2007, 2013 and 2020. Diversity, cover and composition, along with community trait-weighted means and plant strategies were assessed to understand vegetation dynamics and impacts of microclimate changes over time. Growing season length and temperatures have increased in the late melt zone, while changes were less consistent in the early and mid melt zones. There was little fluctuation in diversity, which stabilised over time. However, there were increases in graminoid cover and declines in snowpatch specialists through time in mid and late melt zones. Community trait-weighted means for height, leaf area and leaf weight also increased, particularly in mid and late melt zones, while plant strategies shifted away from compositions of ruderal-tolerant to stress-tolerant. Snowpatch plant communities are changing in response to longer growing seasons and warmer temperatures, with the most pronounced changes in areas where snow persists the longest. The results demonstrate the loss of defining biotic and abiotic characteristics of snowpatches as they approach ecosystem collapse. However, further research is required to assess how factors such as plasticity of snowpatch specialists, snowpatch seedbanks and changing biotic interactions may influence snowpatch plant communities as the climate continues to warm.