A Systems Ecologist with the Council for Scientific and Industrial Research in South Africa, Bob Scholes delivered a keynote address entitled "Forests matter; dry forests matter most" at Forest Day 5 in Durban, South Africa, on December 4, 2011. The transcript of his opening plenary speech is attached as a link below. His talk included a slide that cast some light on the way in which global forests act as a carbon sink. 

Even though we took careful notes, the slide went by too quickly. Now that CIFOR has posted the speech online, we can now ponder the meaning of this math at leisure. The diagram is in "petagrams" of carbon, which Bob Scholes explains is the equivalent of "a cube of solid carbon, one kilometre by one kilometre by one kilometre in dimension."

Click to enlarge diagram