| Description: |
Rapid environmental changes in the Arctic tundra are driving shifts in herbivore populations, distribution, and phenology, affecting the structure of herbivore community. These changes will have consequences to ecosystem structure and function through the direct effects of herbivores on vegetation biomass and biogeochemical cycles. Yet, the effects of herbivores on ecosystem functions, particularly within a multispecies context, are still poorly understood. Addressing these knowledge gaps in tundra rangelands, which are grazed by both wild and domestic herbivores, is an urgent task to ensure the development of sustainable management practices. Using Icelandic rangelands as a case study, I investigated how changes in herbivore communities affect tundra ecosystem functions across various spatial and temporal scales, with a focus on nutrient recycling. Specifically, I aimed to: 1) track changes in herbivore community composition through time, 2) assess the impact of herbivore on vegetation biomass, 3) measure the faecal nutrient contributions of different herbivores species, and 4) evaluate the role of herbivores on nutrient distribution. I analysed long-term data to assess shifts in herbivore populations and their impacts on vegetation at a regional scale. Additionally, through extensive fieldwork in 2022, I examined herbivore effects on vegetation, faecal nutrient deposition, and nutrient transport at landscape and local scales in high-elevation rangelands. Specifically, I measured rates of aboveground biomass consumption, faecal nutrient content and faecal deposition rates of pink-footed goose, sheep and reindeer, and forage quality at 21 sampling sites throughout the growing season. Near-infrared reflectance spectroscopy (NIRS) models were calibrated to estimate faecal nutrient content. Results from the thesis indicate rapid changes in the Icelandic herbivore community: over the past 40 years, the dominant herbivores shifted from domestic (mainly sheep) to wild herbivores, led by the large increase in ... |