I am Judith Sitters, a biologist and FWO post-doc at the Vrije Universiteit Brussel. But the adventure I’ve captured here began two years before I started in Brussels, thousands of kilometers to the north. For two years, I worked as a post-doc in Sweden, at the university of Umeå, a city situated about 600 kilometers to the north of the capital, Stockholm. The winter temperatures here can drop to 20 degrees below zero when the days are only 4 hours long, while in summer, the sun never goes down. As I am a tropical person (I grew up in Zambia and Kenya), I had reservations about this move, but I could not pass up the chance to work with one of the world’s most prominent reindeer researchers.

This photo was made in June (!), and the abundant snow made it impossible for us to reach our experiment. We came back two months later.


On the other hand, it’s great to take a nap in the sunny tundra.


My job as an ecologist involves studying the exciting interactions between soil and plants, as well as the effect of large herbivores on this system. Plants need nutrients to grow, such as nitrogen and phosphorus. The growth and diversity of plants in a certain location is closely connected to the amount and balance of nutrients they can find in the soil. Large herbivores, such as horses and cows, influence the diversity of plants, not only because they are selective about which types of plants they eat, but also because they deposit nutrients in the soil through their dung.

My research in Umeå focused on the effect of reindeer on soil processes and plants in the arctic tundra. My field work took place in Reisadalen, Norway, another 950 kilometers further north. The reindeer there belong to the Sami, the originally nomadic people that live in Lapland, but primarily wander around in the wild. A so-called reindeer fence runs right through my study area. This fence was built in the sixties, and helps the Sami herd the reindeer from the summer pastures to the winter pastures. The reindeer are herded towards the fence, which they then follow until the herders open it, and allow the reindeer to pass to the other side. The fence separates an area that is heavily grazed in summer from an area that is barely grazed at all during winter, as the reindeer only migrate through the winter area, and don’t graze much in it. In this way, the fence provides a natural experiment, allowing you as a researcher to compare an area that is heavily grazed by reindeer with an area that is lightly grazed.

The arctic tundra in Reisadalen, with the reindeer fence in the center of the picture. To the right of the fence the tundra is only lightly grazed by reindeer and is therefore still dominated by the original shrubby tundra vegetation. The tundra to the left of the fence is grazed heavily by reindeer, which transformed the vegetation into a grass-rich pasture.


A herd of reindeer in the heavily grazed area.


Me, with a baby reindeer we found without a mother. Luckily, mom quickly came back to get her baby, but not before we made some cute photos.


With the help of field assistants, I collected soil and plant samples from the heavily and lightly grazed areas. Afterwards, we looked at how much nitrogen and phosphorus we could find in those samples. I also measured the growth or productivity of the vegetation through a fertilization experiment. In this experiment, we added nitrogen and/or phosphorus to the vegetation. These nutrients were then taken up by the plants, which reacted with an increase in their productivity. In this way, it is possible to determine which nutrients the plants need most. In other words, by which nutrient their growth is ‘limited’. If a plant community is limited by for example phosphorus, its productivity will only increase with the addition of phosphorus. It would not increase if you were to add nitrogen or another nutrient.

Here I am, in the field, identifying tundra plants, which means that I determine which family and species they belong to.


Here, we are measuring the distribution of the plant species and the coverage of our experimental plots. We do this using the ‘point intercept method’, by driving thin pins into the ground. If a pin makes contact with a plant, this gets registered. In the end, the number of contacts over a large number of pin positions is summed up, which allows us to estimate the coverage of the different plant species.


We gathered soil samples in the lightly and heavily grazed areas. Nitrogen and phosphorus concentrations in these samples were measured in the lab, to determine to what extent these nutrients were available to plants in the field.


Here, my field assistant is fertilizing experimental plots with nitrogen and/or phosphorus.


Here, my field assistant is gathering all the plants in the plot, two years after fertilization. These plants were later weighed to calculate the biomass production per fertilization treatment.


Here, the clipped plant material is being sorted into functional groups, such as grasses, herbs and shrubs. This material was later dried and weighed to calculate the biomass production per fertilization treatment.


The results of my research show that there is less phosphorus in the soil in relation to nitrogen, if the area is heavily grazed by reindeer. This means that the vegetation is limited by phosphorus, which can have all kinds of effects on the vegetation itself, such as changes in the composition of the vegetation and the growth of alien plant species. Phosphorus limitation can also have negative effects on the reindeer themselves, since they need a relatively large amount of phosphorus when they are young to grow and to develop their antlers. An important challenge for the future is to gain a better understanding of this effect of reindeer on plants, themselves and the entire ecosystem.

It can get rainy, cold and misty in the tundra.

Luckily, even in the tundra, there is always time for a coffee break during field work.

The results of my research can be found in two published articles in Ecosystems and Functional Ecology.

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