There have been many reports out there of tree damage caused by Roundup, young trees are most susceptible because of their thin bark, but it can enter at the base of any tree if sprayed on the root flares or suckers.
Read here
Monsanto says it won't enter through the roots because glyphosate is immobile in soil—how true that is I don't know.
There probably isn't enough contamination in the leaves of large trees to be overly concerned about, but the good news is bacteria are able to mitigate glyphosate, so composting like fortyonenorth recommends would be the safe way to go.