It's a weed crazy party back there, I just moved in this house in November, the yard has its....obstacles! Here are a few plants that I found around the base of the pecan tree. I believe the first picture is just baby pecan trees, I have them all over the yard, and they seem to be coming from the roots in the ground.
The appears to be Chinese Elm, a rather weedy and commonly planted street tree. The second is too blurry to know for sure, but is likely a seedling from a tree in the area. Black Cherry and Poplar both come to mind as possibilities...neither are desirable. The third is a Smilax sp. also known as catbriar. It can be a tenacious weed and has thorns. I have no idea about the fourth picture. Sadly, they're all weeds, and all should be pulled up. The catbriar may prove to be difficult and may require chemical treatment. It comes up from the roots again and again.
