Thorny Viney tangled mess taken over state park
I took these photos a few days ago (January 2020) so maybe that's why there are no leaves on these thorny vines, but there are still lots of green stems. Taken at Pocomoke River State Park Shad Landing on Maryland's lower Eastern Shore. The thorny vine tangles are so dense and so pervasive that you can't walk through the woods. Are these native or invasive?
Worcester County Maryland
This is likely our native Smilax roundifolia, a.k.a. Greenbrier.
Here is our page on it: https://extension.umd.edu/hgic/topics/greenbrier
Once it has leaves it should be quite identifiable with rounded leaves.