Waterlogging of soil induces diverging rates of senescence in Svalbard reindeer forage plants

As climate change is unfolding faster in the Arctic than in any other biome, thermal and hydrological changes are predicted to reshape Arctic ecosystems. Water availability is expected to affect the end of the plant growth season, a time period essential for accretion of fat stores in Arctic herbivores, influencing their survival. We experimentally tested how different levels of soil moisture influenced timing and rate of senescence of a grass (Alopecurus ovatus), forb (Bistorta vivipara) and dwarf shrub (Salix polaris), important forage plants for a keystone herbivore, Svalbard reindeer (Rangifer tarandus platyrhynchus). Moderately increased soil moisture slightly delayed the timing of senescence in the forb and shrub. However, waterlogging reduced the growing season of the forb and shrub but considerably extended that of the grass. In “saturated” (waterlogged) plots, 40 percent of initial grass biomass remained green until the end of the experiment (onset of snow and frost), compared to <10 percent in “elevated soil moisture” and “control” plots. These results indicate that soil moisture moderates rates of plant senescence, with some species benefiting from saturated soils. Waterlogging soils may extend the time period over which flood-resilient grasses senesce, to the nutritional benefit of Arctic herbivores such as Svalbard reindeer.