REINDEER GRAZING IN A NORTHERN BOREAL FOREST : Seasonal and reindeer-induced changes in nutrient availability and soil temperature

Sammanfattning: Soil nutrient availability is a key component to understanding the boreal ecosystems, as it directly relates to plant productivity and ecosystem diversity. There is however little known about how the nutrient availability changes seasonally in the boreal forest. This study aimed to understand how soil temperature and nutrient availability changed seasonally as well as with or without reindeer grazing. This was done through measuring NH4, NO3, PO4, total N, and C:N ratio in soil samples taken in- and outside a reindeer exclosure in northern Sweden and then analyzing for differences over sampling time, grazing treatment, and the interaction of both. Differences in soil temperature were more extreme in the grazed areas, giving higher summer temperatures and lower winter temperatures, due to a decreased layer of insulating lichens. Increased soil temperatures also resulted in lowering the C:N ratio, possibly by enhancing the microbial activity leading to larger amounts of CO2 being released. No nutrients differed by grazing treatments, possibly due to the system being complex enough to contain contradicting effects. No systematical differences in seasonal nutrient levels could be found, which was deemed as surprising, but opens for the possibility of sampling one time being sufficient to have an approximation of nutrient levels all year round