msmith
ArboristSite Operative
Poplar burns hot & fast as others have said. Try to leave the rounds/splits large as possible as it helps the length of burn.
Thing is, cottonwood and poplar are two different species. I've also noticed that cottonwood quality varies from tree to tree and from within the same tree. It's a mixed bag.
Tulip Poplar isn't a poplar, it's a Magnolia. The name makes it confusing.