Myrsky Eero: The warming arctic, herbivore outbreaks and the importance of long-term field studies

Myrsky Eero: The warming arctic, herbivore outbreaks and the importance of long-term field studies

In our latest post, Myrsky Eero, a PhD student at the University of Helsinki, presents his work ‘Higher vascular plant abundance associated with decreased ecosystem respiration after 20 years of warming in the forest-tundra -ecotone’. He discusses the importance of long term research, presents the complex trade-offs happening in ecology and shares his passion for cold places.

About the Paper

The Arctic is warming as much as four times as fast as the globe on average and for cold adapted ecosystem this means one thing for sure: there will be changes. One major consequence, and a motivation behind this study, is a phenomenon called Arctic greening, meaning that certain trees and shrubs are spreading and growing taller. This has an effect on many ecosystem functions such as nutrient cycles, snow accumulation, albedo, NDVI, litter quality, micro climate and species distributions just to name a few. Arctic soils also store a huge amount of carbon and one of the big questions is what will happen to this carbon in a warming world.

In the summer of 2018, we re-visited a warming experiment that was established in Abisko, northern Sweden back in 1998 and has been running ever since. The vegetation of the warmed and control plots was surveyed twice before: in 1999 and in 2009. In 2018 we resampled the vegetation which gave us a nice time series on the effects of warming on sub-arctic plant communities. We also measured CO2 fluxes through the growing season.

We were interested if the previously detected vegetation trends were still ongoing or if the dynamics had changed during the past nine years. By 2009, the two dwarf-shrub groups, evergreens and deciduous, were the most dominant growth forms in the warmed plots. Interestingly, by 2018, they were still dominant, but due to several herbivore outbreaks, the abundance of evergreens had declined, whereas deciduous species had kept increasing. It seems that the increased abundance in response to the warming which was observed in 2009 may not be cumulative over time. However, one deciduous species, the dwarf birch (Betula nana), was able to increase in abundance despite the outbreaks. This led us to conclude that in the long-run, the species that are most likely to thrive in the warming Arctic are the ones which can both benefit from the warming climate and also recover quicker from intense herbivory, such as moth outbreaks, which are predicted to become more common and severe in the future.

International Tundra Experiment (ITEX) open top chambers (OTCs) placed on the study plots. These chambers increase the temperature of the plots by around 1.5 °C (Credit: Sari Stark).

The earlier research found that the different quality of litter produced by either the evergreen or deciduous species should affect the ecosystem’s CO2 exchange, deciduous litter being more easily decomposable than evergreen. In our study the warmed plots acted as stronger carbon sinks and the total abundance of all vascular plants, not any particular plant group, was associated with decreased ecosystem respiration, i.e. the release of carbon from the ecosystem into the atmosphere. We concluded that even if in the short-term the different quality of litter can affect the ecosystem carbon fluxes one way or another, in the long-term the microclimate and soil cooling caused by taller and denser vegetation, irrespective of any particular plant group, can decrease the carbon loss from the system by decreasing ecosystem respiration.

Chamber used to measure CO2 fluxes (Credit: Myrsky Eero)

About the Research: Implications and Context

Our results highlight the importance of disturbance regimes for the responses of vegetation to warming. Indirect impacts of increased plants on soil microclimate may also become increasingly important for CO2exchange in the long run. In cold adapted ecosystems, everything tends to happen at a slower pace and therefore a long enough time is needed to properly understand these processes. This is why I think that the maintenance and re-surveys of long-running field experiments are so important, and hope that our study will add a useful piece of information for a better understanding of the changing Arctic. I certainly hope that I get a chance to revisit this study site again in the future and add yet another chapter to this field of research.

Landscape of Abisko with lake Törneträsk in the background (Credit: Myrsky Eero)

About the Author

I have a deep passion for the nature of remote and cold regions of the globe and for this reason, my current work revolves around the changing sub-arctic plant communities. First and foremost, I have always been passionate about spending time outdoors; in fells, mountains and forests. Spending a lot of time in these places made it natural for me to start developing a special interest in them and a growing desire to understand them better. This is what ignited my scientific spark. The next logical step for me was to pursue a degree in biology.

As soon as I learned that there is a biological field station in Kilpisjärvi in Finnish Lapland, I knew it was a place I wanted to go. I gathered the data for my Masters thesis there, graduated, and have since visited Kilpisjärvi and many other sub-arctic research sites several times as part of different research projects. At the moment, I am a PhD student at the University of Helsinki. I enjoy the possibilities that my work offers being out in these fascinating places and, when it comes to the actual science, I think it is extremely important for us to understand how these ecosystems function in a rapidly changing world. Mountain glaciers are melting, permafrost is thawing, and species are re-distributing… the list goes on. The more we know, the better we can prepare and respond.

Myrsky Eero in Greenland back in 2016 doing his thing: surveying plants and measuring gas fluxes (Credit: Juha Kaarlejärvi).

Enjoyed the blogpost? Read the research here!

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