That Portland report is a good start, but the "over 48 pounds" figure is a general average. Fast growing trees like poplars or pines can absorb a lot more, especially when they're young. The type and age of the tree makes a huge difference.
Threw some poplars in my backyard a few years back and they've been soaking up CO2 like crazy. That fast growth really does make a difference in the early years.