Poplar IS a hardwood... so your statement makes no sense.
As for the OP, I do not bother with the poplar (or cottonwood) that we have around here any more. I can get all I want for free, but I pass on it for better wood. Why load the wood racks with low energy wood? The most common type in the PNW is black cottonwood, also called California poplar and balsam poplar. Burns fast, has the smell of cat pee when burned, takes a long time to dry, and it simply is not worth it. It has a tad more energy than most eastern poplar types, but it is still pretty low in terms of heat. Tulip or yellow poplar is much better, but that is actually a type of magnolia, and not in the poplar family. Aspen is similar, and not worth it. I also pass on Tree of Heaven, willow and white pine. All low heat woods.