What was done
The authors, as they describe it, "used meta-analysis on plant community measurements from standardized warming experiments at 11 locations ["relatively evenly distributed among alpine, Low Arctic, and High Arctic areas"] across the tundra biome involved in the International Tundra Experiment," where passive warming "increased plant-level air temperature by 1-3°C, which is in the range of predicted and observed warming for tundra regions."

What was learned
The 27 researchers report that "overall, warming increased height and cover of deciduous shrubs and graminoids, decreased cover of mosses and lichens, and decreased species diversity." Of the seemingly negative phenomenon of biodiversity loss, they say that it "may result from differences between long-term and short-term warming effects, as local extinctions and shifts in dominance are likely to occur before immigration," which in the natural world ultimately compensates (or more than compensates) for the local loss of species that may migrate poleward in latitude and upward in altitude in response to global warming. That this is likely to be the case in the face of widespread rising temperatures is further suggested by the well-known fact that in the real world of nature there are, as the authors acknowledge, "broad patterns of increasing diversity along natural gradients of increasing temperature."

What it means
The demonstrated tendency for warming to increase the height and cover of deciduous shrubs in tundra ecosystems greatly increases their capacity to sequester increasingly larger amounts of carbon and thereby slow the rate of rise of the air's CO2 content (see Carbon Sequestration (Peatlands) in our Subject Index). It also presages an ultimate increase in local biodiversity.