Thanks for all the thoughts and suggestions. I don't really know how hard cattle or other livestock would be on mature trees in other regions and management systems, but I know that lots of trees can survive the pressures of livestock in my system: in my pasture rotations (mostly along the edges but within the paddocks) I currently have a sycamore, pines, alders, red oaks, black walnuts, red cedars, and tulip-poplars, and they've all done fine. Tulip-poplars and red cedars seem like they might be harder to get through the earlier years but not too hard. I hadn't initially thought pecans for a few reasons. I'd be interested in hearing your thoughts on these issues. First, pecans are such a large tree that they'd give me more shade than I'd need for the animals, and I don't think I want that extra competition with the grass. Secondly, pecans seem like awfully small nuts to try to find in pasture-type grass. Would bush hogging be sufficient to get the grass down low enough to find most of the nuts? Thirdly, what about manure contamination? I would want the shade most of all in the summer. Could I let manure fall under the tree all summer and then safely harvest the nuts immediately afterwards? On the one hand, I figure I need tall trees to grow above the reach of the livestock, which would make a crop that fell to the ground practical, but on the other hand, there are the issues of manure and finding the crop in the grass, so that leads me to think relying on ladders might be a good compromise. Any suggestions for a particular mulberry cultivar? Some varieties seem to have more tree-like form than others. I think I'd want a tree with a trunk that went straight up beyond where cattle could reach and then formed its canopy. ORwoods, you mentioned figs. I do have some figs near my barn, and I've noticed when I've had animals on leads walking past my figs (or when they've gotten out of the fence) that they've never seemed interested in the fig bush. Are there specific varieties of figs that could better be trained to more tree-like form (as with the mulberry)? What about kaki persimmons? Would they even get big enough? Could I get extra height/trunk by grafting a kaki 6 foot high on a D.v. rootstock? Could that work?

Judging from the looks of the second tree (with a stray branch sticking out), it looks like these might be pruned a bit to stay that skinny. Can you take a picture of the leaf or a close up of a branch?

I agree with saltcedar - the very invasive "Tree of Heaven" (also called "stinking sumac" but it is not a sumac). After cutting it down, dab some brush killer on the cut stumps, especially around the outer edges. Retreat if it sprouts again.

If the leaf is shiny, I believe it is Morus alba, the non-native white mulberry. That is what I've heard. The native Morus rubra has a dull upper surface.