Well, the old rule of thumb is that if they are more than 25 years old, ie, large DBH, like yours, that they probably do have resistance/tolerance. Mind you, as a tree gets old, its resistance will fade as it gets frail. Many of the resistant varieties offered for sale started as cuttings off a found tree....one found surviving when the others in the area have died. Some folks are starting cuttings off whatever healthy trees they find that they can get permission to take slips from. You need green wood, current years growth before it gets woody, and a bit of rooting hormone....3000 to 8000 PPM of IBA in talc.

There are a number of large elms in my city that appear to be American elms that miraculously escaped Dutch elm disease. As it turns out, they're slippery elms, which are less susceptible to the disease. Slippery elm leaves have a sandpapery feel to them vs. smooth for American elm and the seed pods are round vs. mostly round with a notch at the top for American elm.

ditto what Hurtle said.

Also be aware that true American Elms can have partial resistance, so that they may actually be losing some branches at the top that you would not notice, or they can just be lucky. Also note that DED is carried by a beetle, if for some reason and American elm is not attractive to those beetles, then they are not going to be exposed. So a tree completely susceptible to DED could still end up not being infected and killed, due to the beetles having no interest. So in short, you have two selection pressures occurring at the same time.

Arktrees

Two things, and this is my personal take on things only, so take it for what you wish:

if it's still alve, it may be resistant, if it's dead, it's not

you can buy tested resistant selections, Valley Forge grows well here, and plant one in your woods for the genes to introgress.

Many of the resistant/tolerant selections that are now tested were foud by just that means. ...take cuttings off healthy trees, plant all in one spot and grow out and innoculate the seedlings. Those that look ratty for a year and then recover by themselves are good. The Universities of Guelph and Fredericton are doing just that. If you are an eternal optamist, go for it, and let us all know how the little trees make out.

There should be some resistant trees, perhaps yours are among them.
Down here on the edge of hell, DED has had no visible effect on either the large Cedar Elm population or the small American Elm population. Don't know if our trees are resistant or the bugs can't take the heat or both.

Ok - HURTLE - thanks! I checked half of them, 3 are slippery elm, 1 is American elm, based on the leaf texture. I didn't realize that subtle distinction, so thanks for the education. The leaves have quite a rough texture, and are quite distinctive.

I'll check the others this week, but a couple don't have any lower branches.

Disappointing that they're not all American elm, but at least I've learned how to distinguish between them.

I have not heard that rule of thumb about 25+ year old trees. Here is a quote from an elm researcher:
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""We would get numerous cuttings from people who believed they had an ancient survivor growing in their yard," says Schreiber. "But we soon discovered that most of those trees were just lucky. They had simply not been attacked by the elm bark beetle that spreads the disease."

Adds Townsend, "It is not uncommon to find a single elm surviving by chance where others have died."

He estimates that only 1 in 100,000 American elm trees is DED-tolerant. "Most of the thousands we tested turned out simply to have escaped exposure."
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I would guess that your elms have simply not been exposed. If there was really some resistance genetics there, I would expect some trees that are much larger than the one in the picture.

The beetles probably have a hard time finding a few scattered middle aged elms in a mixed species forest. Also, since the beetles don't feed on elms until they are several years old, it may be that, when all the big elms in the area got wiped out, the beetles moved on, leaving a few young trees that grew into the specimens you see now.

Alex

Here is a link that might be useful: source for quote

There are a number of large elms in my city that appear to be American elms that miraculously escaped Dutch elm disease. As it turns out, they're slippery elms, which are less susceptible to the disease. Slippery elm leaves have a sandpapery feel to them vs. smooth for American elm and the seed pods are round vs. mostly round with a notch at the top for American elm.

Concur. We have lots of large elms in Minnesota (and little ones too). DED comes through every 20 or so years and wipes out a bunch more large trees that survived the last go around. There doesn't seem to be any danger of them being wiped out as there are ALWAYS gobs of babies around up to 20-30', but then they tend to die. We also don't have elm yellows up here, so not sure how that will play out.

Most of the elms on my property i let grow until they die, and then they are the PERFECT size for firewood if you don't like splitting wood!

Here are some white elm seeds, the Elmwood seedlot (U. americana), some red elm seeds and a close up of a red elm seedling

white elm seeds, U. americana

these ones are red elm seeds