Close-up of affected area on the worst part of the tree.

Close-up of the tree just starting to show signs.

Looks vaguely ash-like. I don't know TX stuff though. Eric, if you could, give us a trunk shot or two. Is there bark cracking and so on? Point the camera at the base too please.

+oM

Yes, need to see the base. Appears it may be girdled.

Sure thing, I will post some pictures of the base in the morning.

Here is the first tree, the worst one.

..and the second tree which is just now starting to show issues. These trees were planted about 6 years ago when we built the house.

I traced the trail of ants to the mound at the base of this purple lantana plant, which is also starting to turn brown, as compared with its healthy-looking neighbor.

Can you pull the rocks away from the base of one or both of the trees so we can see what it looks like where the tree and the soil meet?

..and from the other side...

It looks like the tree is strangling itself. I can't figure out why the bases of the trees are so thin and then the trees widen out above; were they restricted (wrapped or bound somehow) around the base when they were planted?

Well, the tree was staked at first, which I think is why it has a split down the side, from rubbing against the stake. Aside from that, I'm not sure. We had a landscaper put the yard together, and up until this year, I haven't had any problems with any of them. Now I have several trees of two different species all having the same problem at the same time. While this individual tree might have some issues of its own, it seems like it must be something environmental that is causing the problem. You don't think these ants could have anything to do with it, do you?

Sure is a lot of ant discussion here lately! Must be having a good year. I find it surprising to see both trees with nearly identical full-length trunk wounds. That's bad. The trees may manage to close up those wounds and grow new wood around them, but at the very least, sap flow is impeded on the corresponding sides of both.

I think the bulging areas are just the graft union acting like they usually do. And while there are clearly some roots "strangling" one another, as posted above, not quite sure there's any girdling going on. There could be though-the one side of both trees has a flat look usually associated with such.

BTW, it's not unusual to have a few good years with a tree that is headed for problems from trunk wounds/girdling roots/etc. Trees store lots of energy so they normally exhibit a delayed response to some of this stuff.

Now back to ants: When ants do cause problems for plants, it's usually indirectly, by constantly churning and digging up the soil in said plant's rooting area, causing it to dry out. That is except fot those ants Spruceman brought to our attention which actually do directly attack trees. But they are an exception, not the norm. I surmise that with most of the nation in drought, ants are doing especially well and are especially numerous this year. Hence, every ailing tree also coincidentally has ants on it!

+oM

Thanks for the replies. Do you think I should go after the ants then? Like I said, this is affecting not only the trees I photographed, but also three russian plums, and a third ash tree (if they are indeed ash). It doesn't seem likely that they all have root/trunk problems that are all manifesting themselves at the same time. Which is why I'm thinking it's something that affects all of them. I just don't have much experience with this, so I'm not sure what else to check.

I don't know Eric...looking at the last pic again, it's almost as if there's been some graft incompatibility. It really does swell out in that area. I had an "Autumn Purple" white ash once which I really tried to provide good conditions for. Truth is, no matter what I did, it just continually got worse. Finally, the bark on the lower trunk was cracking and branches started to outright die off. Tree had no chance. That problem with that cultivar is a known entity. What is your tree BTW? It does look like an ash but what kind?

And no, I was saying the ants are incidental, not causal factors.

+oM