Small mammals are widely recognized for their impacts on ecosystem properties, but little is known on how their population dynamics influence biogeochemical cycling and ecosystem function. The Nutrient Recovery Hypothesis (NRH) describes the effects of lemming population cycles on arctic vegetation and soils and provides a framework of how population cycles may influence ecosystem function. The hypothesis predicts for the high phase of the lemming cycle to shift tundra towards a carbon source and for the low phase to shift the system towards a carbon sink. Support for this hypothesis has mainly been supplied through the above-ground effects of historic lemming populations, such as changes in vegetation cover and primary productivity, while below-ground effects and contemporary population cycles have been relatively unexamined. We tested if the NRH is still supported under a contemporary population cycle by examining the effects of simulated population changes on above-ground (vegetation % cover and NDVI) and below-ground variables (soil temperature, thaw depth, total soil carbon (C), nitrogen (N), and phosphorus (P), inorganic and organic forms of CNP, microbial biomass CNP, and CNP-acquiring enzyme activity) over three years near Utqia?vik, Alaska.

Here we present our preliminary results. We observed effects of lemming population peaks on above-ground factors, such as decreasing graminoid (sedge) cover and a pattern for increasing primary productivity (NDVI). However, we found no below-ground effects except on soil temperatures, which were higher following a population crash, and microbial biomass C, which was higher when lemmings were present than when they were absent. We conclude that our data provide limited support for the NRH under contemporary conditions and that future lemming populations may provide feedbacks for shifts towards stronger carbon sink processes in the Arctic.