From the CO2Science Archive: Cornus florida L. grows throughout the eastern part of the US except, oddly enough, in most of Florida. It has pretty Spring flowers and is non-toxic to horses making it a good shade tree for horse farms. In 2000 there were a pair of experiments under low-light and high-light conditions showing an average of 121.5% extra growth with an extra 300 ppm CO2. So if the climate policy crowd make us switch to horse and buggy at least our horses will have plenty of shade.