Secondary metabolites in Betula nana ssp. nana : Effects of browsing intensity and nutrient availability

The ongoing shrubification of the Arctic tundra may in the future have serious consequences for the ecosystem. More trees and shrubs will lead to changes in species composition and may alter diversity, carbon and nutrient balance, and result in a lower albedo. Reindeer can reduce the spread of shrubs, but plants have developed chemical defenses against herbivores made up of secondary metabolites. The concentration of these can be affected by several factors, including damages from herbivory and the availability of nutrients. In this study samples of the shrub B. nana ssp. nana (dwarf birch) and soil samples were collected from outside and inside herbivore exclosures in Fennoscandia. Then, concentrations of phenols and terpenes, the major defense component in birches, and soil nutrient availability were analyzed. A proxy was created for measuring the density of reindeer at each location. The aim was to evaluate this data and see if the exclusion of herbivores or the nutrient availability had any effect on the concentration of the defense components. Few differences between the exclosures and control plots could be found and only two out of 18 t-tests showed any difference that was deemed statistically significant. The density of herbivores was found to have no effect and the nutrient availability showed no clear results. This study concludes there are many factors influencing the concentration of defense components in dwarf birches, including the rising temperatures, that need to be considered in future studies. A better understanding of this subject would be essential in visualizing the future of the Arctic tundra