I've been thinking for long about a process to make cheap trees. Of course the available trees in the HO scale train market are much better but they are also stupidly expensive.
This Brandywine scenario requires a lot of them and so I tried my favourite material to work with: hard styrofoam (Roofmate).
First you cut cubes (or whatever shape you want) from styrofoam 4cm plate, the one you use to isolate the roof or walls of your house.
Then you glue them together with a hot glue gun. Don't forget the tree trunk. Barbecue sticks or old paint brushes, I use them all.
The most important part comes next while you use a soldering stick to open holes and crevices all over the styrene until a tree like shape is obtained.
As it is winter you get a nice warmth but also a stinky smell, so forget winter and do it in an open area!
Finally you use some cheap modelling paste and stick it around the end of the trunk to simulate surface roots. While the paste is drying you can carve the small roots in it.
Finally glue to the MDF base some loose bits of carved styrene all around to look like boulders.
Now painting: paint everything black mixed with PVA glue to strengthen the acrylic paint. No spray as it will damage the styrene.
Then apply greens, yellows and browns according to your taste.
Another advantage of these trees is that you can make a large group like this one just in a few hours all along maybe two or three days allowing drying time.
These trees are cheap and you can't make two alike, like in nature.
I'll show you soon how my Brandywine table is going and you will see that these trees goes well alongside the commercial available ones (I hope...😰).