Arctic plant/climate coupling across space and time

The Arctic system acts as a `hub of feedbacks', where ice-related processes interact non-linearly and amplify changes in the regional/global climate. On non-glaciated land, the energy and carbon budgets of high-latitude vegetation drive several such feedbacks. I present results linked to two key questions on Arctic land plant-mediated climate interactions:

Negative feedbacks, top-down controls, and spatial scales. Negative feedbacks contribute to climate change mitigation. Top-down controls on vegetation from herbivory have been shown to increase albedo and below-ground carbon accumulation, and to delay permafrost thaw. Can these processes occur over regional scales, impacting the Arctic and Earth systems? MODIS imagery was used to explore regional-scale effects of reindeer herbivory on the plant/climate relationship in Yamal (NW Siberia), home of the Earth's largest reindeer herd. Reindeer signatures on plant/climate relationships were inferred regionally within a dominant landform-mediated signal. I also report on a longitudinal remote sensing study on the effects that the introduction in 1996 of a guild of large herbivores had on land cover in Pleistocene Park (Chersky, NE Siberia), and discuss on the scalability of such initiative.

Temporal scales. Do the plant/climate relationships reported in the Arctic during the observational period hold when interrogating longer proxy records? Will the warming tundra keep on "greening"? In Yamal, mechanistic shrub growth models using δ¹⁵N from annual rings highlight the role of topography and nutrient limitation: 24 out of 24 analysed shrub individual were found to be N-limited, whereas ring-width was temperature-dependent in 17 out of 24 shrubs. Plant-soil feedbacks (litter recycling) were found to be important, and this was modulated by topographic wetness. A multidecadal increase in plant uptake vs. available N was detected, suggesting nutrient limitation as a fundamental modulator of Arctic plant/climate relationships. Looking further back into the centennial/millennial scales, I discuss the role of Pleistocene refugia in modulating the present plant-climate relationships, and address whether extant Arctic megafauna can provide the top-down negative (mitigating) feedbacks inferred from the fossil record at the biome scale in the next decades.