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Difference between fenced area and grazed area in lichen cover. Photo: Maria Väisänen

Exclusion of reindeer for twenty years did not affect the nutrient status of the pine forest soil and dwarf shrubs

9.6.2021

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 lying on the ground.
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