Is Roundup used for all of the trees' lifetimes or only in the first (maybe second) year in order to prevent it from being overgrown? My father now owns a litt

Is Roundup used for all of the trees' lifetimes or only in the first (maybe second) year in order to prevent it from being overgrown? My father now owns a little bit of forrest and after new trees had been planted the effort for keeping them growing and not dying under tons of weed is non-trivial. As soon as the trees are big enough the issue becomes a non-issue, of course.