Diminishing forests, eh? They must’ve migrated because of all the fossil fuel burning in Europe at the time. Those damn stone age SUVs.
In WWII the Germans developed a jet fighter fueled by coal.
The further you go back in time the less coal there is, you would have to go back and use to the organic matter in its original state before it became coal.
They had to move because the wood they used for their jet aircraft was nearly used up and thats how we know how they all did it on that one particular Wednesday...jet aircraft.