That looks like a very large old dogwood. I can't be sure of the species but red ossier and gray dogwood both occur in Minnesota. It probably is the Gray Dogwood because red ossier has very distinctive red twigs and young branches that are ornamental and very visible in winter.
First one is unmistakenly Buckthorn. It's everywhere in MN.
Second one is a different tree right? Black Cherry would be my guess. Big Buckthorn can look like that too but that would be a huge one and they tend to coppice at some point rather than stay one trunk at that size.
If you have a few buckthorn trees rip them out by the roots, if you have a forest of them like me... well good luck.
I am experimenting on several permiculture techniques for buckthorn control. One of my theories is cutting the trees low to the ground late in the fall and cover cropping them with crown vetch, radish, and burdock. Then chop and drop mulching the whole lot several times. We'll see, buckthorn is a terror to get rid of.
On reflection, I agree. I didn't think of buckthorn at first because the species we have here is the non-invasive Carolina buckthorn which looks quite a bit different. The common buckthorn leaves are very similar to Dogwood (which we also have, but the bark is somewhat different). And that second photo could very well be a mature buckthorn. Check out this pic (last one) of a mature tree. http://www.portraitoftheearth.com/trees/buckthorn.html
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