Hans Cornelissen joined the international Tundra Trait Team of ecologists, who collected and analyzed the most comprehensive data set on plant traits at almost 120 locations above the natural tree line in polar and alpine regions. Until now, this area was mainly the domain of low-growing plants. However, the team show in their Nature paper that taller plants are steadily taking over this cold environment as a result of global warming. The team, headed by lead author Dr. Anne Bjorkman, found that not only have individual plants grown taller with warmer temperatures, but that the plant community itself has also shifted over only three decades. Taller plant species, especially shrubs, have spread across the tundra, either from warmer pockets within the tundra or from southern or lower elevation areas. The tundra has long been a focus for climate change research, as the permafrost underlying tundra vegetation contains one-third of the world’s soil carbon. When the permafrost thaws, greenhouse gases could thus be released. An increase in taller plants could speed up this process as taller plants trap more snow in winter, which insulates the underlying soil and prevents it from freezing quickly and deeply in winter. The Nature paper was the result of a massive plant trait measurement campaign, assembly of trait data available from databases and subsequent data analysis. These analyses were discussed and started during two workshops at the German Center for Integrative Biodiversity Research (iDiv) in Leipzig, which Hans participated in. Data for several key leaf traits related to plant growth rate and tolerance of cold and nutrient stress were also collected. They showed interesting patterns too, but the magnitude and direction of change depended on peculiarities of different tundra sites, especially on whether they were dry or wet. In a follow-up paper, some of the authors including Hans are looking into how these changes in leaf traits cause change in the quality of the dead leaves and their break-down rates. Such change could, in turn, also have consequences for soil carbon loss and climate.