In his doctoral thesis, physical geographer Pekka Niittynen investigates the wide-ranging ways in which snow conditions affect the arctic mountain environment and what kind of effect the reduction of snow cover in the coming decades will have on it.
In his studies, Niittynen identified the absolute necessity of snow for northern biodiversity. Snow contributes to the maintenance of the diversity of floral splendour that gives pleasure to visitors to the northern wilderness.
In Arctic mountains, snow is layered unevenly. Wind blows it off ridges and knolls into thick snow drifts in sheltered hollows and on slopes. This also makes snow melt at different times in different places. Late-melting snow beds can be found on Finnish fells as late as in September. This results in a spectrum of growth sites, each presenting a unique community of species. However, this spectrum is now under threat.
The enchantment of Lapland and snow
“I was already entranced by the nature of Lapland as a 10-year-old kid when my father took me on my first hike to the Utsjoki wilderness,” Pekka Niittynen says. While Niittynen began studying geography at university, Miska Luoto, who had extensively studied features of northern nature, began working as a professor at the department. Luoto was eventually appointed Niittynen’s thesis supervisor. Now, Luoto and Niittynen are both working in the BioGeoClimate Modelling Lab research group.
“From the beginning of my studies, I knew the topic that I wished to explore in my research career,” says Niittynen who is carrying on, thanks to funding awarded by the Maj and Tor Nessling Foundation, his research on snow and its links to the structure and distribution of arctic vegetation.
There remains more to investigate in the field of snow and winter conditions, as the effects of climate change on arctic vegetation have so far been studied and modelled particularly through the prism of summer conditions.
“The overall significance of snow has of course been acknowledged ages ago, so there's no point in a southerner such as myself educating residents of Lapland about how many links it has to a range of things,” notes Niittynen, who has spent a great deal of time carrying out fieldwork around the Kilpisjärvi Biological Station. “To science, however, my research clearly has something new to offer. In many models, snow has been entirely overlooked,” Niittynen adds.
Passion for arctic research
Snow presents a challenge to researchers, as related measurements are quite arduous to carry out. Modelling snow cover, which varies greatly in thickness even at a distance of a few metres, has been difficult. In his work, Niittynen has utilised accurate satellite imagery to monitor snowfall, coverage and melting in arctic environments. This way, there has been no need to visit the research area in wintertime to measure every square metre individually.
In the summer, the researchers have travelled to the arctic mountain region, going over thousands of plant plots from which they have surveyed the species present to determine which snow conditions each species prefers.
“Knowing the coordinates, we are able to link the site with snow data calculated from the satellite images and, for example, with the average amount of time the site annually stays under the cover of snow,” says Niittynen.
Many arctic areas are difficult to access by researchers, with varying conditions putting their patience and cold tolerance to the test. In addition to the arctic mountains of Northern Finland and Norway, Niittynen’s research has taken him to Greenland and Svalbard.
“We wanted our research to cover a broad area to enable us to make generalisations across the Arctic as feasible as possible. We found that the characteristics of vegetation are governed by largely similar environmental factors from Lapland to Svalbard,” Niittynen notes.
The arctic region is favourable to researchers specialised in plants in that many species occur throughout the tundra bordering the Arctic Ocean. Those familiar with the fell plants of Kilpisjärvi also fare quite well in Greenland. For the future of arctic nature, the fact that most of the species have more than a single population is indeed a good thing.
Research aims to understand the present and predict the future
Predicting the future takes some skill, but Niittynen has developed scenarios on the future development of the snow cover as well as utilised vegetation models based on current knowledge to forecast the locations where snow conditions favourable to individual species will be preserved, or whether there will be such conditions at all in the future.
“Our models are based on understanding the current growth site requirements and ecology of plants well enough to be able to predict what might happen to different species in a changing climate,” Niittynen continues.
“One of our main findings is that the species associated with late-melting snow have the highest risk of disappearing if climate change progresses according to the worst-case scenarios. Glacier buttercup, one of the northernmost flowering plants in the world, and other species accustomed to very cold conditions are in danger.”
Not succumbing to pessimism
“I believe snow cover can also be a saving factor to many species in milder climates. After all, rainfall is predicted to increase in northern regions, and if even a portion of that will continue to fall in the form of snow, snow drifts in the north can also remain thick in the future. Of course, the duration of the snowy period is quite likely to shorten considerably,” says Niittynen.
“That said, the further warming of the climate in southern Finland, where winter temperatures are already close to or even above zero, will eliminate the little snow we have. Then again, we don’t have a similar range of species specialised in conditions where the snow cover is thick,” Niittynen adds.
The research was carried out in close cooperation with the University of Helsinki and the Finnish Environment Institute SYKE. Pekka Niittynen wishes to thank Risto Heikkinen, a researcher at SYKE, who, alongside his thesis supervisor, has made an indispensable contribution to his doctoral thesis.
Pekka Niittynen, MSc, will defend his doctoral thesis entitled ‘Arctic vegetation, snow and the global change’ on Thursday, 10 September 2020 at 12.00 at the Faculty of Science, University of Helsinki. The public examination will take place in auditorium P673 of the Porthania Building (Yliopistonkatu 3). The public examination can also be followed remotely.
Three of the articles included in the doctoral thesis have already been published:
Niittynen P. & Luoto M. (2018). The importance of snow in species distribution models of Arctic vegetation. Ecography. https://doi.org/10.1111/ecog.03348
Niittynen P., Heikkinen R. & Luoto M. (2018). Snow cover is a neglected driver of Arctic biodiversity loss. Nature Climate Change. https://doi.org/10.1038/s41558-018-0311-x
Niittynen P., Heikkinen R. & Luoto M. (2020). Decreasing snow cover alters functional composition and diversity of Arctic tundra. Proceedings of the National Academy of Sciences. https://doi.org/10.1073/pnas.2001254117