What was done
In the words of the authors, "an ecosystem process model, BIOME-BGC, was used to explore the sensitivity of net primary productivity (NPP) of an oak (Quercus liaotungensis Koidz) forest ecosystem in [the] Beijing area to global climate changes [projected to be] caused by increasing atmospheric CO2 concentrations."

What was learned
For a doubling of the atmosphere's CO2 concentration from 355 to 710 ppm, the Beijing oak forest's NPP was calculated to rise by 14.0%; with a concomitant temperature increase of 2°C, its NPP was calculated to rise by 15.7%; and with an additional 20% increase in precipitation, it was calculated to rise by 25.7%.  Last of all, with a 20% increase in precipitation and a 4°C increase in temperature, it was also calculated to rise by 25.7%.

What it means
In contrast to typical climate-alarmist claims, many projections of ecosystem responses to potential environmental change are not catastrophically negative, even when the increases in air temperature they employ are unrealistically large, such as the 4°C rise used here.  In fact, as in this particular case, many of the responses are actually positive, and strongly so.  One of the reasons for this discrepancy is that climate-alarmists typically downplay, or even disregard, the many mitigating effects of concomitant atmospheric CO2 enrichment (which they claim is the driver for climate change and therefore cannot be ignored), including the ability of elevated levels of atmospheric CO2 to (1) dramatically increase plant growth (see our Plant Growth Databases Dry Weight and Photosynthesis), (2) significantly reduce plant water loss by transpiration and thereby (3) greatly enhance plant water use efficiency, and (4) actually alter the physiology of plants to where they prefer warmer temperatures, which phenomenon is expressed by an increase in the temperature at which plants photosynthesize most efficiently (see Growth Response to CO2 with Other Variables (Temperature) in our Subject Index).  Any projections of ecosystem responses to potential climate change, and especially those that assume the rising CO2 content of the atmosphere is their cause, must include these very real phenomena.  And when they are included, the results are often positive, as was the case in this study.