Tim Johnson,
The elms are in all different sizes. As a general rule, the larger dead elms produce larger patches of mushrooms. In my video "22 Lbs. Motherlode under a Dead Elm," you will catch a glimpse of the large trunk. Even the little saplings can produce well, but it's easy to walk by them because my eyes are peeled for the larger elms. Yes, it is the Dutch Elm disease that has been killing the elms. Most other trees such as ash, poplar, sycamore, cedar, etc. don't have to be dead to produce. A dead apple tree can be good. Thanks and good luck!
Duke, Yep. It was private land. Thanks for watching and happy hunting!