Runa Magnusson discusses her recent article: Spatiotemporal variability in precipitation-growth relations of Betula nana in the Siberian lowland tundra.
Warming, greening, thawing – The Arctic is a place of rapid warming and environmental change, with temperatures increasing three to four times faster than the global average. Impacts on Arctic ecosystems and communities include, among many other processes, declines in sea ice, snow and glacier extents, changes in vegetation composition, expansion of shrub vegetation and degradation of permafrost. Despite these fundamental changes, the Arctic also remains a very inspiring place for researchers and travellers. I for one felt very lucky to be able to go on fieldwork to a less travelled corner of the Arctic for my PhD: the Indigirka Lowlands of North-Eastern Siberia.
Shrub growth under climate extremes – The Siberian Indigirka Lowlands have shown very high climatic variability in recent years. The past decades have seen heat waves, extreme snowfall and several very wet summers. This made me and my co-authors wonder how shrub growth would respond to such a series of extremes, compared to general observations of shrub expansion under general climate warming. In addition, we wondered whether differences in topography – and, as a result, in wetness, microclimate and snow dynamics – would affect the response of shrub growth to climate change. To broaden my research group’s earlier studies of climate-growth response of the widely distributed Arctic shrub Betula nana, we sampled shrubs from a range of landscape positions.
I first sampled shrubs from wet depressions and shrub patches in low elevation areas (a “drained thaw lake basin”) during my first field season as a PhD in 2018. Circumnavigating the pandemic, co-author Sergey collected additional sample material from a somewhat higher elevation site in 2020 (a ridge composed of “Yedoma”, carbon- and ice rich permafrost soils). We waited eagerly for several months for the sample material to pass through customs and arrive from Yakutsk to the Dendrolab of Wageningen University in the Netherlands.
Living archives – Dendrochronology, or the study of tree rings, offers researchers insight into multiple decades of plant growth. Each year, the stems of woody trees and shrubs produce a discernible layer of tissue, making them “living records” of their own annual growth. But measuring tree rings in Arctic dwarf shrubs can be very challenging. Betula nana shrubs in the Siberian Arctic reach heights of about 20 centimetres, and their stems usually have diameters of less than a centimetre. Still, these stems can contain about 50 or up to 80 tree rings. To complicate matters, shrubs can show “missing rings” due to occasional inactivity. Researchers use a technique called “serial sectioning” to reconstruct time series of annual growth. This is done by comparing multiple stem cross-sections within an individual shrub, and then comparing and matching series among different shrubs. Hence, the study of tree rings in Arctic shrubs under the microscope can be a puzzle. But in the end the highly detailed and beautiful images of wood tissue and the resulting time series of shrub growth are very rewarding.
Complex responses to precipitation extremes – We compared our timeseries of shrub growth with local weather data, split over different topographical subsites and different time periods. This way, we could assess whether relations between climate and shrub growth differed across topographical gradients and across time periods and derived several lessons. Over time, shrub growth timeseries from the various subsites (wet depression, shrub patches and a higher elevation ridge) showed a very comparable and stable association with summer temperature. However, association with summer temperature was stronger in years that also showed high rainfall, indicating that the extent to which shrubs can benefit from high temperatures is also determined by water availability. In addition, the different subsites showed diverging responses to snow depth and rainfall over time, which appeared to be related to the occurrence of extreme snowfall and increasing rainfall variability over time. This suggests that shrub growth response to precipitation inferred under a limited range of precipitation variability may hold little information for future growth under anticipated increased in precipitation variability and extremes in Arctic regions.
Going forward – On a more personal note, we are very grateful for the beautiful collaboration we have had among Dutch and Russian scientists and rangers at the Chokurdakh Scientific Tundra Station. This is a very remote station in a type of Arctic environment (Siberian lowland tundra) that is underrepresented in scientific literature. We are continuously improving our understanding of regional and local drivers that shape the response of tundra ecosystems and Arctic plant species to climate warming. Let’s aim for broad and diverse future collaborations across the entire Arctic biome.
Runa Magnusson, Wageningen University, Austria
Read the full article online: Spatiotemporal variability in precipitation-growth relations of Betula nana in the Siberian lowland tundra
