Ecol. Lett. http://doi.org/jb4 (2012)

Arctic tundra — a biome typically covered with low-lying vegetation such as mosses, sedges and dwarf shrubs — is, in many places, changing its structure towards increased shrub abundance. It is not yet clear what effect this change in plant community structure, sometimes called 'shrubification', will have on Arctic ecosystem carbon budgets and their contribution to future climate change.

Sean Cahoon, from the Department of Biology at Pennsylvania State University, USA, and co-workers have now made inroads into this issue by investigating the midsummer carbon dioxide flux from 21 sites spanning 16° of latitude in Arctic and boreal biomes. They found that during the summer, shrub sites with warm soils (above 10 °C) were net sources of CO2, whereas shrub sites with cold soils (below 10 °C) were strong sinks. These findings indicate that the transition to a shrub-dominated Arctic will increase the rate of carbon cycling, which, the authors suggest, could lead to net carbon loss if soil temperatures rise sufficiently.