Maybe xmas trees could perform those functions, I don't know though. As a starting thought the pine needles create acidity don't they and the needles don't break down very quickly. BUT there are varieties that don't shed needles.
The tree's main value (imho) is the provision of benefits for the crop, so inputs are reduced to very little. The crop rotation would be more diverse as diversity drives these systems. IF we end up with payments for provision of ecosystem services the AF system would maximise that whilst maintaining food production.
I'm not saying this is the only solution but AF's got a lot going for it if food production and sustainability are to co-exist.
of course the lowest labour/ most simple use of a tree is as a climate change prevention device ...... plant and forget
to be viable though people need to start paying for the service the tree provides .... i can see that coming maybe ?