The ORNL conducted FACE experiments where  levels were increased above ambient levels in forest stands. These experiments showed:
* Increased root production stimulated by increased , resulting in more soil carbon.
* An initial increase of net primary productivity, which was not sustained.
* Faster decline in nitrogen availability in increased  forest plots.
* Change in plant community structure, with minimal change in microbial community structure.
* Enhanced  cannot significantly increase the leaf carrying capacity or leaf area index of an area.
FACE experiments have been criticized as not being representative of the entire globe. These experiments were not meant to be extrapolated globally. Similar experiments are being conducted in other regions such as in the Amazon rainforest in Brazil.