Hi -- I know some of the answers to your questions. American plum self-fertile -- seems to be. I had 2 and then cut down one after it got old and started to go - the other still seems to bear well. There are other plums around the yard, plus various wild Prunus species in the neighborhood, plus various oranmental plum and sandcherries in the neighborhood as well. 2) 5 x 5 foot size. Yeah, I don't see a real problem with it. My 2 American plum seedlings grew naturally to about 7 to 8 feet max, with probably a 6 to 8 foot spread. So, with a little pruning, probably not too much of a problem. 3) Partial shade -- definitely. My surviving one is in about 2/3rds shade now, as the trees around it have gotten larger, and it seems perfectly happy as an understory type tree. It still gets pretty good light because the two trees near it are a Kentucky Coffe and a Sycamore, and both don't start to branch until very high off the ground. 4) Taste -- Well, the fruits of my plum are quite tasty when fully ripe and slightly soft. They have a bit of astringency when not fully ripe. They make wonderful plum sauce, jelly, baked tarts, etc. I've never had the Chickasaw plum, so can't comment. I did plant a beach plum last year, but it's still only a foot tall.

wildlifeman, If these are groves of suckering native plums, then the suckers are genetic clones of the original seedlings in these clumps, and the fruit will be identical to those you are so fond of. The native Chickasaw plums here in the Southeast sucker prolifically, and it's a simple thing to dig a few suckers and transplant them - Voila! you'll have your own plum thicket in virtually no time. Air layering might work, but digging suckers in the dormant season and transplanting will be much easier - and establishment will probably be faster as well. I'd be marking some likely prospects now, for digging this fall or late next winter. Some of these native plums root relatively easily from cuttings, so if you'd care to give that a try now, you don't have much to lose.

it is unlikely that the suckers will produce fruit that is tasty, but depending on the rootstock, they may produce fruit. You could graft scion material from any, or all the named plums you have onto these suckers for you neighbor though.

Ironically, I have the opposite challenge: a semi-desperate quest to propagate an heroic purple plum before it is completely dead. No luck, so far, in germinating pits or in rooting cuttings. The fruit comprises the prettiest and tastiest plums I've experienced in half a century; foliage is lovely, and the tree plows on through the searing, arid climate. Borers love it to death, too, though, and I gather that fruit trees can be rather short-lived, anyway. Maybe the edge-of-the-desert conditions in north Texas suppress "suckers" here: I've never seen a single one in a decade-and-a-half or so.