This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Reindeer grazing changes the vegetation of northern pine forests below ground as well as above it. In a recent study in Finland, trees and understory vegetation in grazed forests had nearly 30% less shallow-root biomass than those in ungrazed areas.
Root structure also changed, which may affect the ability of plants to take up water and nutrients. The research is published in the journal Oikos. Changes in pine-forest root systems associated with reindeer grazing may affect forest carbon and nutrient cycling.
The impacts could be significant across reindeer-grazed boreal forests worldwide. Boreal forests as a whole store around one-third of the world's terrestrial carbon, with most of that carbon stored in soils. The researchers collected and compared soil samples from dry pine forests in Angeli, Raja-Jooseppi and Kätkäsuvanto in Finland.
The sites were either grazed by reindeer or had been fenced to exclude reindeer grazing for 50–100 years. The study showed that reindeer grazing reduces the quantity of tree and understory roots, particularly in the uppermost 0–5 cm (0–2 inches) of soil, where most root biomass is found. Root abundance is influenced by the quantity and composition of vegetation as well as soil temperature.
In the pine forests studied, reindeer grazing had thinned the insulating lichen cover, exposing the soil to greater temperature fluctuations. In reindeer-grazed areas, winter soil temperatures were well below freezing, reaching as low as -10°C (14 degrees Fahrenheit), compared with ungrazed areas, where the minimum temperature only rarely reached -5°C (23 degrees Fahrenheit). "Winter cold and frost damage in particular may help explain the reduced amount of roots in reindeer-grazed areas.
Mechanical disturbance caused by reindeer, such as trampling, may also contribute to the reduction in roots," says postdoctoral researcher Maria Väisänen of the Water, Energy and Environmental Engineering Research Unit at the University of Oulu, Finland. The study also found that reindeer grazing changes roots, making them shorter, thicker and less branched. "The changes indicate reduced exploration for nutrients and water, as the roots became structurally less exploratory," Väisänen says.
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