Windbreaks can have several advantages for a beekeeper. The function itself, wind-breaking, is an advantage on its own, because reduced winds make it easier for the bees to forage, something I suspect is not usually considered. Then, the trees will provide 3 main ingredients: pollen, nectar, and/or resin. Considering which of these resources your bees may be most lacking would be a good first step in choosing what to plant. Then you need to consider when they need it. Need early pollen? Willows, perhaps. Nectar in the season? Linden? Ideally, windbreaks should have more than one species, and even better if you don't use the same clone (cultivar) for all of those in the same species in order to widen the timeframe of usefulness.