Just prune them off. Here's a good reference.

https://www.gardeningknowhow.com/ornamental/trees/sand-cherry/pruning-plum-leaf-sand-cherry.htm

not a long lived tree ... and at 30 feet ... probably long into its life span ...

id love to see a pic of the whole tree ... since ive never seen one that size [probably a MI thing] ... also.. where are you.. that they grow that big???

anyway ... if it is really old.. MAYBE ... the tree itself is starting to fail ... and the massive root system is responding.. by trying to put out another tree or a hundred ...

even if that were the case.. im not sure there is any way to predict such ... nor anything you can do about it ...

if the sprouts end up different.. say green ... then you would know it was grafted ... and the green tree roots are taking over ... at that point... i would probably be done with them ....

to be clear.. i am speculating.. since you asked us to speculate ...

ken

i dont see any here.. that look 30 feet to me : https://duckduckgo.com/?q=Purple+Leaf+Sand+Cherry+Tree&t=ffcm&iax=images&ia=images

if you dont mind taking the pic of the whole.. lean a common garden shovel against it ... then snap the pic.. presuming its the common 5 foot long shovel ... we can then use it as a scale ... or measure you shovel.. if you dont mind ...

At that size, it's probably Prunus cerasifera (purple leaf plum/cherry).

A hard winter with some top damage to the inner bark, could cause the tree to sprout more from the bottom but being we have no idea of your location or growing zone, this too is just guessing.

Agree with Bill........30' is exceedling tall for a sand cherry. Anything more than 10-12' would be highly unusual, whereas 30' or more is common for a purple leaf plum tree, P. cerasifera. And basal suckering is extremely common with these trees. Just one of many of their common drawbacks.

i was suspecting plum also.. but expected to hear about black knot issues ... lol ...

i was wondering about that stuff that you can put on crabs to reduce basal suckering ... could it be used on this tree??? .. or is it malus specific??? .. i dont have the right search terms to find it ....

ken

It’s called Sucker Stopper. No clue if it works.