Manipulative experiments allow a mechanistic understanding of ecosystem responses. The use of consistent local experimental designs replicated across broad environmental gradients in a coordinated way, allows examining larger-scale ecological questions, while controlling for differences in methodology. Experimental manipulations of the diversity of herbivore assemblages, by excluding different species at a time, will help understand their separate and combined impacts on the functioning of tundra ecosystems. The common experiment will use exclosures with different mesh sizes to manipulate the level of herbivory by different groups of vertebrate herbivores.
WP2 lead: Elina Kaarlejärvi
The most productive habitats at each site, which are in turn the ones most used by herbivores, will be targeted for setting up the exclosures. We will set up five replicate large exclosures, 5 x 5 m with a 50 cm gap above the ground restrict access of large herbivores like reindeer or muskox, but allow access of smaller herbivores (e.g., hare, ptarmigan). Within the large exclosures, smaller plots (1 x 1 m) will be established to exclude medium sized herbivores (5 cm mesh size) or all herbivores (1 cm mesh size, dug into the ground).
Within each plot we will quantify above and belowground processes, including plant productivity, plant nutrient content (C, N), soil nutrient availability, decomposition rate (using the TeaBag Index), and plant-microbe interactions (e.g. abundance of ectomycorrhizal fungi, soil microbial biomass). These proxies for different ecosystem functions will allow calculations of ecosystem multifunctionality. We will also estimate herbivore pressure at each site by using pellet group counts and the ratio of plant biomass outside/inside of exclosures, to assess the combined and separate effects of different herbivores. TMS-4 loggers will be installed (ideally a minimum of four per site) to continuously measure soil and air temperatures, as well as soil moisture.