Keith - I don't know the cemetery of Mons, but there are other types of German war cemeteries I have seen and worked at.
Damvillers near Verdun was a mayor centre of the rear area with an Army hospital; there the dead were buried in rank an file under recently planted trees in a regular pattern.
Near this town in Lissey every unit buried their dead in a small forest; there is no recognizable pattern. Some are buried in lines, some in circles around a stone with the units name, sometimes with no place to go between the single parts of the burying ground.
The trees were mostly no oaks.
Often single oaks are planted to commemorate a jubilee or an outstanding event. Around my house are two such oaks. The first planted to commemorate the birthday of Jahn, founder of the German Turner-movement, and the other at Oct. 3, 1990 - the day of the reunification of my divided fatherland. On this occasion I swung the shovel happily.

Wilfried