Background
The authors write that "changes in climate and atmospheric CO2 and nitrogen (N) over the last several decades have induced significant effects on forest carbon (C) cycling." But they go on to state that "contributions of individual factors are largely unknown because of the lack of long observational data and the undifferentiating between intrinsic factors and external forces in current ecosystem models."

What was done
Working with over four decades (1956-2001) of forest inventory data that they obtained at 3432 permanent sample sites in maritime and boreal regions of British Columbia (B.C.), Canada, along with continuous flux measurements acquired at three chronosequence forest sites, Wu et al. describe how "growth enhancements were reconstructed and partitioned into contributions of climate, CO2 and N after removal of age effects," which they accomplished with the help of the process-based InTEC model (Chen et al., 2003) that considers the role of stand development when simulating various forest processes.

What was learned
In the words of the eight scientists, "we found that climate change contributed a particularly large amount (over 70%) of the accumulated growth enhancement, while the remaining was attributed to CO2 and N, respectively."

What it means
When all was said and done, Wu et al. concluded the report of their study by stating that "climate warming is contributing a widespread and significant growth enhancement in B.C.'s forests," which they implied was a doubly-significant positive phenomenon, in light of the fact that in addition to the obvious growth enhancement benefit, "forest ecosystems that sequester carbon from the atmosphere play an important role in Earth's carbon budget by offsetting the increase in atmospheric carbon dioxide caused by fossil fuel emissions and land-use change."

Reference
Chen, J.M., Ju, W., Cihlar, J., Price, D., Liu, J., Chen, W., Pan, J., Black, A. and Barr, A. 2003. Spatial distribution of carbon sources and sinks in Canada's forests. Tellus B 55: 622-641.