| Summary: | The Arctic is warming at double the average global rate, affecting the carbon cycle of tundra ecosystems. Most research on carbon balance drivers from Arctic tundra ecosystems has focused on abiotic environmental controls (e.g. temperature, rainfall, or radiation). However, Arctic tundra vegetation and therefore the carbon balance of these ecosystems can be substantially impacted by herbivory. Here, we test how vegetation consumption by brown lemmings (Lemmus trimucronatus) can impact carbon exchange of tundra ecosystems by altering carbon dioxide (CO2) and methane (CH4) fluxes. We placed brown lemmings in individual enclosure plots within a wet-sedge tundra ecosystem near Utqiaġvik (formerly Barrow), Alaska. We established nearby control plots to indicate the state of the tundra vegetation in the absence of herbivory. We also introduced indirect predator cues to some enclosures to record the effect lemmings alone and lemmings in presence of predators may have on vegetation consumption. We tested the impact of these treatments immediately after lemming removal and during the growing season the following year using a greenhouse gas analyzer to estimate carbon fluxes. A spectroradiometer was used to evaluate vegetation health via NDVI (normalized difference vegetation index). Our results show that lemmings significantly decreased CO2 uptake (nullifying ecosystem carbon sequestration), while not affecting CH4 emissions, but that vegetation recovered the following growing season. We suggest that herbivory temporarily damaged aboveground vegetation tissues reducing NDVI and CO2 sequestration but did not affect CH4 emissions, likely because CH4 is produced at depth. We also found no significant impact of predator cues on carbon fluxes or lemming foraging behaviors. Synthesis. Lemmings decreased CO2 uptake, but did not significantly impact CH4 emissions. Aboveground biomass disturbance removed photosynthetic tissue, decreasing carbon sequestration by Arctic tundra vegetation communities. There is no evidence that ...
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