Increased nutrient availability speeds up permafrost development, while goose grazing slows it down in a Canadian High Arctic wetland

Abstract

1. It is of prime importance to understand feedbacks due to the release of carbon (C) stored in permafrost soils (permafrost-climate feedback) and direct impacts of climatic variations on permafrost dynamics therefore received considerable attention. However, indirect effects of global change, such as the variation in soil nutrient availability and grazing pressure, can alter soil and surface properties of the Arctic tundra, with the potential to modify soil heat transfers toward the permafrost and impact resilience of Arctic ecosystems.2. We determined the potential of nutrient availability and grazing to alter soil energy balance using a 16-year split-plot experiment crossing fertilization at different doses of nitrogen (N) and phosphorus (P) with protection from goose grazing.Moss biomass and some determinants of the surface energy budget (leaf area index (LAI), dead vascular plant biomass and albedo) were quantified and active layer thaw depth repeatedly measured during three growing seasons. We measured soil physical properties and thermal conductivity and used a physical model to link topsoil organic accumulation processes to heat transfer.3. Fertilization increased LAI and albedo, whereas grazing decreased dead vascular plant biomass and albedo. Fertilization increased organic accumulation at the top of the soil leading to drier and more porous topsoil, whereas grazing increased water content of topsoil. As a result, topsoil thermal conductivity was higher in grazed plots than in ungrazed ones. Including these properties into a simulation model, we showed that, after 16 years, nutrient addition tended to shallow the active layer whereas grazing deepened mean July active layer by

Scale‐dependent effects of herbivory on moss communities in Arctic wetlands: A 25‐year experiment

“…However, snow geese can consume up to 60% of the annual production of wetland graminoids in the High Arctic (Gauthier et al., 1995; Valéry et al., 2010). Their grazing can thus alter the competitive balance between mosses and vascular plants by removing graminoid biomass, preventing litter accumulation, and changing the soil thermal profile and hydrology, which indirectly promotes high moss biomass (Deschamps et al., 2022; Gauthier et al., 2004). Our study adds to these effects of goose foraging as we found that goose presence increases alpha diversity and promotes moss coexistence.…”

“…Snow geese probably influence species composition both directly and indirectly; for example, when they grub for rhizomes, they disturb the moss carpet by creating holes that may be colonized by various moss species (Jasmin et al., 2008). In addition, in the absence of grazing of vascular plants, litter accumulates (Deschamps et al., 2022), and competition for light probably limits the growth of moss species (an indirect effect). Thus, snow geese can act as a filter on plant community composition.…”

“…Taken together, these results show that goose herbivory is an essential biotic agent releasing mosses from competitive exclusion by vascular plants. Such top‐down regulation can delay some of the expected changes in plant communities of Arctic wetlands, especially moss communities, in response to climate warming (Deschamps et al., 2022).…”

“…Snow geese primarily feed on above‐ground graminoids and can consume up to 60% of the annual production in Arctic wetlands during the summer (Gauthier et al., 1995; Valéry et al., 2010). Such intense grazing in plant communities characterized by low primary productivity can profoundly impact plant production and community composition (Deschamps et al., 2022; Gauthier et al., 2004; Nishizawa et al., 2021).…”

The Arctic Plant Aboveground Biomass Synthesis Dataset

“…Rather, plant biomass typically has been measured as part of individual research projects, each with its own focus and protocols. For instance, researchers have investigated how plant biomass is affected by climate 23 , 24 , wildfire 25 – 28 , herbivores 29 , 30 , and soil properties such as texture, nutrients, and pH 31 – 33 . Researchers have also measured plant biomass to assess ecosystem carbon storage 34 , 35 , evaluate terrestrial ecosystem models 36 , and map spatial patterns of plant biomass from landscape to biome scales by linking field and remote sensing measurements 37 – 40 .…”