restoring an abandoned orchard

Any thoughts on the best way to restore an old plum orchard? The trees in question haven’t been cared for at least 15 years, maybe longer. There is fruit on some of the trees but alot of it is dropping before it’s ripe. What would be the best steps to take to strengthen the trees?

Is it worth using copper sulfate to kill the lichen (or maybe moss) growing on the trees? There’s a lot of it, but my impulse is just to remove it and not use the copper.

Thanks gaias <3

the lichen itself isn’t a problem but it does suggest the damp air and/or limited air movement. pruning to open up the trees to more sun and moving air would probably be my first priority.

prune them, but it is best to prune stone fruit trees in early spring at flowering.

An initial weed-whacking around the base of each tree will help with air flow too(don't clear it to bare dirt; just knock down standing weeds.)

Thank you for the great advice.