Another consideration is time.
If a guy is 70 years old and it will be 20 years before the trees get big enough to cause problems and there are no kids or grand kids that will inherit the pond and be a problem for and the trees are seen to be of current benefit to the owner, I say go for it.
I see a lot of ponds with trees on the dams, and yes they will probably some day cause problems, but they have been there for 20 years or more so far.
As the standard PBF saying goes, "it all depends". How important are the trees to a person and how long does he expect the pond to last or be utilized?
I left one tree on my son's pond dam (
Reclaiming 50 year old pond ) just because it looked too nice for a shade tree for the 5-8 year old kids to fish from and play under. Was it a mistake? Not if the pond last 15 more years before it causes problems and the grand kids are away and on their own (and likely I'm gone too). It will have served its purpose.
Trees are a risk factor to the structural integrity of the dam. The question is, are the benefits of the tree worth the risk it creates? Kind of like driving over the speed limit. Is it worth the risk? Some think it sometimes is.
It all depends.
P.S. We get lots of rain here (42" a year) and no, I do not have trees on our pond dams......although my wife wanted them
