I have to ask first, what do you mean by "artificial trees"? If you are talking about pulling fake christmas trees out of the waste stream and using them in your system, that is one thing. If you are talking more about simulating trees, rather than utilizing fake trees, that is another thing.
In the first case, you're bringing into the picture some possible toxins and contamination issues - I don't know nearly
enough about the composition of artificial christmas trees to be comfortable having them sitting out in the weather possibly degrading into my soil. And while you have pulled them out of the waste stream for the moment, you have also bought yourself the problem of disposing of them when you no longer have a use for them. I do not think I see enough benefit there to make up for the negatives I perceive.
But if you mean doing things to simulate the benefits trees provide, then by all means, there are a number of techniques and mechanisms for providing some of the benefits that can be had from trees, as have been mentioned by others - row covers, fences, hoop houses all provide some aspects of benefits that trees can provide. Another possibility might be an arbor with fast growing vines. It could provide shade, wind protection, the vines would provide transpiration that could help with humidity and if nitrogen fixing vines were used, you could get that benefit as well, plus the vines could provide a yield.
Such an arbor could be built to stand for years, it could be made such that you could move it about. Potentially you could get all the benefits of nurse trees except for timber. And you could get them in a matter of weeks, not years.
So, I think an artificial tree in the system is not such a great idea, but I think using an arbor or
trellis with well selected climbing vines could produce a tree analogue that would be tremendously beneficial.