Carbon Cycle

I found this link and thought it was an interesting read.

Poplar trees

In thinking about this more, wouldn't a tree that contains a high carbon content/lb also contain higher BTU content? Clearly this may not be the case since poplar isn't a high BTU wood....or is it simply that poplar grows fast, so poplar removes carbon from the atmosphere faster than say, oak? So it a carbon lb/growth year measurement?

That's a good question, Warren. As I understand it, fast growth trumps density. The big question is: How do you lock up the most carbon per acre per year. In every case I've seen, it's done with fast-growing hardwoods like hybrid poplar. Why hardwood over softwood? I have no idea.