I've never recommended poplar. The one your are considering is a short-lived tree (50-60 years before it starts to break-up)(Populus alba is the latin name). More concerning is that there are many diseases of poplar, and the more off-site the growing location is to what is the ideal spot for a poplar, the more prone they will be to disease. That makes for an ugly, unsafe tree.
I usually recommend white birch (and its weeping cousin), red oak or larch. The two hardwoods are reasonably fast growing, have a good form but do not dominate a site like red or silver maple. Secondly, it is still possible to grow grass beneath them, as they are not that thick. Larch comes in two or three types, and is suitable for moist to fresh areas. It loves to be by itself, and will grow fast once it is established. It is a deciduous needle-bearing tree, so you will have seasonality with it. Again, it is not too thick that your 30x30 area will be mud underneath the tree.
I recommend that you rethink the poplar. There are better choices available.