A study in Oulanka, northeastern Finland, investigated how long-term exclusion of reindeer grazing affects pine forest soils and undergrowth. The effects of reindeer grazing on lichens have been known for a long time, now researchers want to pay attention to mosses as well.

The study showed that the removal of reindeers was
associated with the thickening of the moss cover, which in turn was associated with
subtle changes in the soil nutrient cycle. However, the nutrient economy of
vegetation remained unchanged. The results of the study have just been published in
the scientific journal Oecologia.

Researchers
involved in the study were Maria Väisänen from the
Arctic Centre at the University of Lapland, Hannah
Bailey and Jeffrey M. Welker from the
University of Oulu and Maria Tuomi from the University
of the Arctic in Norway. The work was carried out using the EcoClimate research
infrastructure of the Oulanka research station, where reindeer grazing during the
winter has been prevented since 1994.

Reindeer grazing has a wide
impact on the northern environment. A long-known phenomenon is the disappearance of
lichens caused by intensive reindeer grazing, especially in winter grazing areas.
Exclosure experiments have shown the ability of lichens to recover from grazing.
Until now, less research has been done on how other ecosystem characteristics change
as reindeer grazing ceases. Examples of key functions are soil nutrient stores and
cycles, which determine the productivity of vegetation and, for example, the ability
of forests to sequester carbon.

The new study Plant and soil nitrogen in oligotrophic boreal forest
habitats with varying moss depths: does exclusion of large grazers
matter? showed that the nitrogen content or the proportion of
the heavy isotope of nitrogen in typical forest field layer plant species such as
blueberry, lingonberry and pine seedlings did not react at all to the exclusion of
reindeer grazing for 24 years.

– Also previous studies done in
the reindeer herding area have shown that the removal of reindeer grazing has only
weak effects on forested pastures, says Maria Väisänen.

– The
results we have published thus support the notion that large grazing animals do not
necessarily have very strong effects on the nutrient cycle of nutrient poor pine
forests, despite the fact that the changes in lichens are obvious, Väisänen
continues.

Reindeers outside
the fenced area. Photo: Noora Kantola

The study collected plant
and soil samples from the light and shadow habits of the pine forest, which also
provided more detailed information on how the natural habitat variation of the
forest affects the nutrient cycle in relation to reindeer grazing removal.

– Our findings show that the inherent variation between lichen-dominated
light habitats and dwarf shrub-dominated shadow habitats is a much stronger factor
in regulating nutrient cycles than reindeer grazing, says Professor, UArctic
Research Chair Jeffrey M. Welker who was leader of the research project.

A more novel finding of the study was that the moss cover thickened up to
80% after reindeer grazing. Mosses play a very central role in the functioning of
northern ecosystems, as they dampen soil temperature fluctuations and bind moisture,
which in turn affects the soil nitrogen cycle. The thickening of the moss cover was
associated with an increased nitrogen content of humus, and in particular inorganic
nitrogen increased in the mineral soil layer.

– In addition to
the effects of lichens, it would be worthwhile to extend the research to mosses as
well, when studying the effects of reindeer on various ecosystem services, Maria
Väisänen suggests.

Research article: Väisänen M et
al. Plant and soil nitrogen in oligotrophic boreal forest
habitats with varying moss depths: does exclusion of large grazers matter?
Oecologia 2021.

More information:

Maria Väisänen
Visiting Researcher,
PhD
Arctic Centre, University of Lapland
firstname.surname@ulapland.fi