I imagine the JAs would shade out the young trees, take over the orchard and prove themselves impossible to get rid of.
My JAs grow at least 6-8ft tall and I can't imagine a little fruit tree standing a chance.
It's very windy round here and I tie my JAs in a big kind of bundle, otherwise they'd blow over. Mine would make bad windbreaks, but good tree-squashers...
Can you get chipped tree mulch? If there's tree diseases around I don't recommend it, but a thick, like 15cm, layer straight onto grass (as long as it's not a running variety) will kill it off. When its dead, plant comfrey, sow clover, whatever!
Be careful if you mulch though, it needs to be kept away from trunks or they may rot.
I use windbreak cloth. If I had space, I'd grow a hedge behind it and take it own later, but I don't