Weeds and grass must be prevented from stifling the young tree for at least two years from planting. Eucalypts in particular will not tolerate weed competition. They also love fertiliser. My trees get manure and seaweed in a convenient dried pellet form, twice a year, and some blood and bone or fish waste. I also mow bracken etc.
Some farmers use sheep to keep ground clear once trees are big enough.
Cattle are too energetic around small trees pushing them over by rubbing on them. Geese and ducks are good grazers and will help reduce competing weed growth under trees. Careful work with a weedeater,scrub bar and slasher can turn gorse and bracken into a lawn-like meadow.