I planted some sea buckthorn hoping to achieve something similar. The buckthorn did not do well for one reason or another and moving forward I will be encouraging the spread of clover to help fix nitrogen under my trees.
There is a thread with a lot of good information on nitrogen fixing cover crops here:
i had mine growing in gravel and it grew fast. only mulched around it a few years then it took right off. i didnt like the taste of the berries so i removed them. i might put another pair in of the newer cultivars to try again. they prefer poor well, draining soil.
there are shorter varieties of pea shrub that only grow to 6ft. i got the seeds from esty. i also have autumn olive. speckled alder fixes N but tends to spread and form thickets.
I believe the jury is still out on this. Studies have shown honey locusts tend to get morenitrogen than they should, and they survive in nitrogen poor soils better than non-fixers. The soil around them has been measured to have elevated nitrogen levels, more so than non-fixers. They donāt have the nodules of other fixers, but formations inside the roots seem to suggest they have a primitive nitrogen fixing mechanism different from nodules.
Basically, it quacks like a duck, but it doesnāt look like other ducks.
I really like black locust personally. Itās one of the few trees which can be established on sandy soil in central texas without irrigation and it grows about 10ft/year here despite the drought. Iāve been inter-planting them with persimmons and in 1/4 acre clearings I made in some thick cedar/yapon brush, hoping to shade out the understory and make the land more navigable. Itās too early to say how bad of a problem the suckering will be, but Iāve read that the suckers are completely shade intolerant and the stems seem to lose their thorns after about 2 years, so as long as thereās canopy of trees I donāt think there will be too many thorns at ground level. I canāt imagine it would be any worse than the native yaupon and greenbriar at least.
Black locust are difficult trees to kill if you were to go that route. However, I found itās best to cut them in late summer and then apply a mix of 20% triclophyr and 80% diesel. Just make sure the roots arenāt interwoven with any desirable plants, because it can be transferred between intertwined roots. I have not had it kill other trees but itās possible that it could.