What was done
The authors used an equilibrium (Mapped Atmosphere-Plant-Soil System) and dynamic (MC1, a type of Dynamic Global Vegetation Model) model to simulate potential changes in vegetation distribution and carbon sequestration across the conterminous United States under various climate change scenarios.

What was learned
Although there were strong differences between the two types of models used in their simulations, the authors reported that they generated strikingly similar results.  Both models agreed, for example, that under twice-ambient atmospheric CO2 concentrations, moderate increases in air temperature (below 4.5°C) should produce an increase in vegetation density and carbon sequestration across the United States.  As part of this phenomenon, both models projected an increase in vegetative leaf area index and biomass within arid land areas of the desert southwest, due to CO2-induced increases in plant water-use efficiency.

What it means
According to the model projections, future increases in the air's CO2 concentration will likely increase vegetative land cover and carbon sequestration across the conterminous United States, even if air temperatures rise by as much as 4.5°C.  In addition, the model results suggest there will be a reverse-desertification phenomenon within the arid southwestern part of the country, due to CO2-induced increases in plant water-use efficiency.