Hi,
You can find the formulation from the tree porous media here: Surface Roughness & Porosity | Advanced Modelling PWC | SimScale
If you carefully look at the equations, you will notice that this is a Forchheimer model (i.e. Darcy-Forchheimer with d = 0).
As such, you can derive Darcy-Forchheimer coefficients based on a given tree configuration.
Cheers