Reindeer leave more than hoofprints where they graze. Recent findings contribute to understanding the effects of grazing in Finland’s boreal forests.
Reindeer grazing changes the vegetation we see above ground, but its influence also reaches beneath their hooves. A recent study in northern Finland compared plant roots at grazed sites and in areas where reindeer had been excluded for decades, revealing differences below ground.
Led by researchers at Umeå University in Sweden, with the University of Oulu in Finland as a partner, the study examined how grazing affects the amount, distribution and structure of roots.
A closer look underground
The researchers studied pine forests in Finnish Lapland. Fences built to control reindeer movements created zones that the animals had been unable to access for more than 50 years. This allowed comparisons with nearby grazed areas where other environmental conditions were similar.
Above ground, ungrazed areas had more ground-layer vegetation, the researchers report. To investigate below ground, soil cores were extracted, allowing scientists to examine roots at different depths.
Grazing significantly affected fine roots, defined in the study as those less than two millimetres thick, and which play an important role in absorbing water and nutrients. Their biomass was lower in grazed areas, especially in the uppermost layer of soil, with almost 30% less fine-root material by dry weight than in ungrazed areas.
Fine roots were also found to be shorter, thicker and less branched. The researchers describe this as a potentially significant shift in functional root traits, suggesting reduced exploration of soil for resources.
Possible causes and consequences
Frost damage and disturbance from trampling are possible explanations for the lower root biomass, the researchers suggest. Lichens insulate the soil, and in grazed areas with thinner lichen cover, winter soil temperatures fell lower.
Other explanations received less support. Differences in soil density were small, offering limited evidence that soil compaction from reindeer activity was the main cause. Summer soil temperatures and soil-moisture patterns also did not support heat or drying alone as explanations for the reduction in root biomass.
Differences in root structure may reflect changes in vegetation composition, according to the authors. For example, dwarf shrubs with thin, highly branched roots, such as crowberry, were particularly reduced in grazed areas.
Roots transfer carbon into soil when they die and through compounds released while growing. Changes in root biomass and structure could therefore have implications for nutrient and carbon cycling, the scientists suggest.
Research on the effects of reindeer grazing continues to grow, with another new detail added to the connections between visible changes in forest vegetation and changes in root systems beneath the surface.
Dr. Yana Kirichenko, PolarJournal