Suzanne Simard is a professor of forest ecology and teaches at the University of British Columbia. She has tested theories about how trees communicate with other trees. She used radioactive carbon to measure the flow and sharing of carbon between individual trees and species. She discovered that Birch and Douglas Fir share carbon. Birch trees receive extra carbon from Douglas Firs when the Birch tree loses its leaves; and Birch trees supply Douglas Fir trees carbon that are in the shade.