Raphael S. von Büren recently completed his Masters at the University of Basel, Switzerland. He is an alpine ecologist with particular interests in the ecophysiology of plants. Raphael shares his recent work on the environmental factors influencing the range distribution of alpine plants.
(left) Portrait Raphael von Büren. Photo credit: Raphael von Büren. (right) Research in alpine environments: Raphael von Büren in his preferred habitat during field work for his master’s thesis. Background: Rhone glacier, Switzerland. (Photo credit: Raphael von Büren)
Personal links. ResearchGate
Institute. Department of Environmental Sciences, University of Basel, Basel, Switzerland; Department of Research and Monitoring, Swiss National Park, Zernez, Switzerland
Academic life stage. Masters (completed 2021).
Major research interests. Alpine plant ecology and ecophysiology, field botany, plant identification.
Current study system. Currently, I am working on several plant ecology projects in alpine ecosystems: (1) Under review is a paper where we studied the influence of earlier snowmelt on above- and belowground growth and senescence of alpine grassland. (2) I am part of the current GLORIA (GLobal Observation Research Initiative in Alpine environments) field survey campaign, a worldwide project exploring vegetation changes on mountain summits. (3) In our latest project, we examine non-native species in the Swiss National Park, a protected area in the Central Alps, to set the basis for long-term monitoring, to anticipate potential future invasions and to discuss the implications for management in an alpine wilderness area.
I am fascinated by working in remote, pristine, alpine areas with harsh environmental conditions. High topographic heterogeneity leads to a mosaic of micro-habitats on small scales, resulting in high biodiversity and a variety of adaptations to the local micro-environment.
Recent paper in JBI. von Büren, R.S. & Hiltbrunner, E. (2022) Low winter temperatures and divergent freezing resistance set the cold range limit of widespread alpine graminoids. Journal of Biogeography, 49, 1562–1575. https:// doi.org/10.1111/jbi.14455
Field work. Cover Journal of Biogeography Volume 49, Issue 8. (Photo credit: Raphael von Büren)
Motivation behind this paper. Range limits of alpine plants are largely unexplored and unexplained. Studying the range limits mechanistically helps resolve the very basic ecological questions of why a certain species exists where it does, and why it is absent elsewhere. Understanding where the edges of an organism’s fundamental niche lie is essential for extrapolating its future distribution under changing conditions. Multidisciplinary approaches are needed that combine micro-climatology with plant ecophysiology at a high spatio-temporal resolution, focusing on the actual life conditions of alpine plants in situ.
Key methodologies. In an alpine grassland in the Swiss Alps, we selected 115 microsites (40×40 cm) within a 2 km radius that spanned a diversity of micro-climatic conditions. At each microsite, we assessed soil temperature 3 cm below ground, closest to the plant meristems, year-round with small temperature loggers and derived snow cover duration and thermal conditions from these data. Additionally, we determined soil chemistry and moisture, as well as vegetation characteristics (species composition, Landolt indicator values). Field data were combined with various freezing resistance analyses (electrolyte leakage, tetrazolium vital staining, regrowth capability) in individuals of the two most abundant alpine graminoids on acidic soils in the European Alps (Carex curvula, Nardus stricta) at 38 microsites by employing mixed regression models. Our approach allowed us to address where (field data) and why (freezing analyses) these graminoids occur or are absent. To our best knowledge, our study is the first to provide a mechanistic explanation of the cold range limit of alpine plant species.
Major results. The study demonstrates that low soil temperature extremes (freezing stress) during winter set the range limit of widespread alpine graminoids, and not the gradual action of temperature on growth and development (like it is the case for the treeline). This contrasts the common assumption that freezing resistance during the growing season is critical for plant species distribution. As clonal alpine plant species are very long-lived, a single clear, cold night without snow may set the scene for centuries. Understanding the edges of the fundamental niche is essential to extrapolate the current occurrence of a species to novel situations under climate change.
High micro-habitat diversity due to topography driven snowmelt pattern in the study area. Timelapse movie 2018. (Photo credit: Raphael von Büren, Erika Hiltbrunner)
Unexpected outcomes and challenges. Air temperatures extrapolated from weather stations do not accurately reflect the micro-climatic conditions alpine plant species are embedded in. Therefore, we measured soil temperature at high spatio-temporal resolution in situ to base our findings on ground-truth thermal conditions.
A common challenge in alpine environments is the limited accessibility of the study region in winter due to high avalanche risk. Hence, the freezing resistance was assessed throughout the growing season but not in winter. Taking away the insulating snowpack to access plant material in winter may also induce unwarranted plant responses.
Evaluating foliar freezing resistance in alpine graminoid species is demanding, because the leaves are often very narrow, and cell damages induced by frost injury are not clearly visible as tissue discolouration and necrosis. We employed an electrolyte leakage method with a miniaturized conductivity cell, which enabled us to reduce the water volume for leaking in order to gain high precision for detecting cell damages.
Next steps. As a next step, I propose to explore cold range limits of other alpine graminoid species, using the same methodology we used in our recent paper. Not only to resolve the very fundamental ecological question, why species occur where they do and why they are absent at other places; but also to explore my hypothesis that only some graminoid species reach the upper alpine grassline (restricted by the gradual action of temperature, in analogy to the treeline) and other graminoid species (which do not reach the grassline, e.g., Nardus stricta) are restricted by temperature extremes and freezing resistance (see Bürli et al. 2021, Alpine Botany; Körner 2021, Trends in Ecology & Evolution).
Lab work. (Photo credit: Raphael von Büren)
If you could study any organism on Earth, what would it be? I am interested in general ecological patterns. Therefore, I prefer studies with multiple species. My favourite taxa are vascular plants, or more generally, sessile organisms. It is fascinating to explore the various adaptations that these species have evolved to cope with diverse environments, given their sedentary lifestyle. Expertise in field botany and vegetation ecology enables the “reading” of landscapes. That is, by simply looking at the species composition, one can infer the environmental conditions at a location. In topographically rich alpine environments, steep micro-habitat gradients lead to different plant communities within a few meters only.
Anything else to share? The recent study in Journal of Biogeography represents a condensed piece of my master’s thesis. I conducted most of the fieldwork in summer 2020 close to the Furka pass in the Swiss Central Alps at 2200-2800 m asl. Fieldwork in remote alpine regions requires quite a bit of planning and the cooperation of people with good team spirit is of great importance. I was part of a research team that was working on various ecological projects. We spent 4 months at the Alpine Research Station Furka (ALPFOR, http://www.alpfor.ch), giving up the comforts of home for the sake of science. After this intense time of sharing almost everything, helping each other with field and lab work, surviving harsh weather conditions and being snowed in, cooking together, and having inspiring discussions, it only remains for me to express my appreciation to the entire team, and in particular to Erika Hiltbrunner, Christian Körner and Patrick Möhl. Thank you, folks!