It certainly means more CO2 is being taken up in the global biomass. Not enough CO2 is being taken up by the biomass to prevent global concentrations of CO2 increasing though.
The other worry is that as global land temperatures increase the release of CO2 from soil increases as well (bacteria in the soil will rot vegetation down quicker). So, even though the mass of vegetation over land increases, the carbon in the soil decreases and the land becomes a net source of CO2 rather than a sink. For example Cox et al 2001 : Acceleration of global warming due to carbon cycle feedbacks in a coupled climate model, Nature, 408, pp 184-187