I plant trees haphazardly in my small 1/4th acre formal orchard and in the yards around my house, but this kind of disorder would never do in a much larger silvopasture or hayfield. The solution, called “Mow-hawking” by Phillip Rutter, is shown in his book Growing Neo-Hybrid Hazelnuts. It works with other trees, too!
Basically the idea is to plant trees in straight rows and carefully mow right up alongside the trees to control the grass (I cut this excess pasture growth to make hay). This limits grass growth, and therefore competition, to just a small percentage of the radius around the tree, yet is is efficient from a mowing standpoint since you don’t have to change directions. If your mower side-discharges, you would want it to discharge away from the seedlings if it could injure or bury them. Otherwise, the discharge could make a good mulch. Since I used a sickle-bar mower, the clippings just fall over evenly in the path.
One could also come back and clean up between the trees if they wanted, though this should be necessary, since the trees are above the pasture (this is a key advantage to planting a seedling vs. a seed) and should stay there in this most hazardous establishment year. The point of mow-hawking is to simply LIMIT competition from the pasture plants for water, oxygen, and nutrients (not light). Deep rooted Black Walnut should soon get to a depth lower than where shallow rooted clover and short grasses hang out pretty quickly. Next year, the trees should be at an advantage vs. tender perennials, and should keep that edge until the tree dies or is harvested. The greatest hazard to the trees right now is my mower!
So far, Oaks and Elderberries (which are pretty unstoppable plants) have held up best from our planting in March, at nearly 100% survival, despite an unusual nearly April-long drought followed by 6 inches of rain (flooding) in the first week of May! It seems that about 20-30% of the Walnuts may have been lost. The Butternuts, Pecans, and Persimmons are all doing better, and in that order.