Did those trees, before there were decomposers, have access to nitrogen fixing bacteria? Where were they getting ammonium and nitrate?
Just stuff built up from lightning, nitrogen and oxygen?
Edit: Looks like land dwelling soil forming bacteria started in the Cambrian. Then, in the Ordovician the first land plants. Then, in the Silurian vascular plants and trees appeared.
Plate of olives and a liter of beer used to be my go-to after work wind down snack.