Trees and shrubs at the northern treeline

by Agata Buchwal, Ylva Sjöberg, Pawel Matulewski

Air temperature observations show that the Barents region is currently the most rapidly warming region on the globe. For better understanding how the climate has varied in this region longer back in time and beyond the record of direct observations, we measure the growth rings of trees and shrubs from the northern treeline. The width and characteristics of the growth rings can be correlated with climatic variables and thereby used to reconstruct past climates.

Photo: Example of a tree core taken from a Scots pine tree in the study area located near NIBIO Svanhovd research station.

We came to NIBIO Svanhovd station in August 2022 to collect wood samples from pine trees and juniper shrubs and explore their potential for such climate reconstruction. Juniper shrubs can be found all the way to the coast and can therefore be used as a climate archive also beyond the northern treeline. We had recently collected samples in northern Sweden and found that junipers can reach an advanced age, occasionally more than 400 years. They also contained some interesting features which suggest that some years, probably coinciding with major volcanic eruptions, had extremely harsh growing conditions for these shrubs. Our samples from the Pasvik valley may tell us if this pattern could be seen across the larger region or if growing conditions vary much across the region for Juniperus shrubs growth.

Photo: Coring of a Scots pine tree in the study area located in the Pasvik Valley

The Pasvik Valley offers fantastic pine forests, which have partly been logged but which still contain some very old pines, even outside of the national park. At the NIBIO Svanhovd station, we were lucky to run into Erik Sørensen who was sampling wood from trees in the area for the state forest inventory for determining ages of trees in the forests. From him, we learned that the oldest pine that they had sampled from the area was 477 years old. We will not know how old our samples are until we have analyzed them in the lab, but samples from such old trees could be very interesting for climate reconstructions.

Photo: Example of irregular but also very interesting juniper shrub disc (i.e. cross-section of a main stem) taken in the Pasvik Valley.

The road through the Pasvik Valley is severely damaged from frost and the small gravel roads that could lead to some of the best sampling locations were full of holes and rocks. For some reason, we had rented a WV Golf – not the ultimate choice for this area. But what you don’t have in your head you need to have in your legs, so we ditched the car where the road got too bad and enjoyed hiking through these beautiful woods. Next time, we will probably budget for a different rental car.

While pines are easy to spot and notice in this area, small juniper shrubs were not something that most people we interacted with at NIBIO had paid much attention to. But we did get some helpful advice on where old shrubs could be located from Paul Aspholm, who has been working as a researcher at the NIBIO Svanhovd station for more than two decades. Discussions about the local climate and human impact history with Paul were helpful for understanding where we might find the suitable shrubs. After our previous experience of sampled junipers in Sweden, we had an idea of what a good habitat for old shrubs would look like. We started looking at relatively dry sites on south facing slopes near the treeline but were surprised to find that the best juniper stands in the Pasvik Valley were quite different. In the end, we found very nice shrubs along the edges of blockfields in the forest. But we also had sampled shrubs close to the coastline. In total, we harvested 111 juniper shrubs and cored 80 trees in the region. We are very glad for this wonderful opportunity to work in the north-easternmost edge of Norway. We took an important lesson and performed insightful observations on woody plant growth at the northern treeline of the European continent. We also got a great NIBIO Svanhovd research station tour together with a research activities overview presented by Cornelya Klutsch.

We left NIBIO Svanhovd station in a rental car that smelled of the the multiple bags full of pine and juniper wood we have collected during our stay. The stay at the station has been great and we have really enjoyed the comfortable rooms, the food, the gardens, the sauna, and the national park exhibition. This great service meant that we could focus on science and nature during our stay, and to interact with other researchers and staff at the station. Having found so much good material leaves us enthusiastic for the coming work in the lab where we will find out the age and sensitivity to past climate of our pines and junipers and compare them to our samples from northern Sweden. But this will take time. We look forward to a lab phase of our project. After that, we can try to solve the puzzle of how the trees and shrubs at the northern treeline have responded to past climates.

Photo: Our dendro team (from the left: Agata, Ylva and Pawel) happy after successful sampling of trees and shrubs at the northern treeline.

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