Antarctic moss carpets facilitate growth of Deschampsia antarctica but not its survival

The vegetation of the Antarctic tundra is dominated by mosses and lichens. Deschampsia antarctica, the Antarctic hairgrass, is one of two vascular plant species which grow along the west coast of the Antarctic Peninsula. However, little is known about its recruitment and interaction with non-vascular tundra plants. Although several authors propose that tolerance and/or competition should be the main forms of interaction between moss carpets and D. antarctica, no relevant studies exist so far. We investigated whether positive interactions are predominant at the Shetland Islands and the west coast of the Antarctic Peninsula and focussed on the role that moss carpets play in the recruitment of D. antarctica. Across the studied zone, D. antarctica showed a significant association with moss carpets, with higher frequencies as well as more and larger individuals than on bare ground. At one site, we conducted moss removal and seedlings transplant experiments to assess the relevance of the moss carpets for different life stages of hairgrass. All experimental individuals survived until the following summer whether the moss carpet was removed or not, but growth rate was significantly lower in tussocks with moss carpets removed. Likewise, tiller size was higher in plants growing in moss carpets than on bare ground. The detected positive interactions with mosses seem to be important for the expansion of D. antarctica, raising the question about their importance under future climate change scenarios.