I found this stuff at Michaels. It comes in 4' rolls and is about 1.5" wide. It appears to be moss attached to a bronze colored mesh. A little dull coat should take the shine of the mesh. Primed Tiger added for scale.
It cost about $3.00 a roll
Tactics are the opinion of the senior officer present.
If you want a quick and dirty forest, poke some flat headed nails into a base to represent tree trunks, paint accordingly, then scrunch up some of that roll stuff to make the canopy. Just sit it on the nails. You can then lift the canopy to move elements among the trees, then put the canopy back on top.
I would not use nails, one person falls, loses balance. Use wooden dowels or plastic railroad trees, would be my suggestion. Just have a kid or someone fall on the nail, medical costs, liability, the pain, etc.
Was going to leave this alone, but seeing as it was my post that started it, and there may have been a misunderstanding of what I meant, I thought I'd clarify...
when I said use flat head nails I mean the kind used for panel sheeting; they have a large circular head about 5 or 6mm across. It may have been interpreted that I meant to use the head as a base for the trunk, but I meant to hammer/push the point into the base and use the flat head to support the canopy. With multiple nails to represent the trunks of trees, I have walked over these 'trunks' and been well supported and suffered no inconvenience, let alone injury. I do not use the styrene foam base boards, I have traditionally used particle/chip board. A comparable base of dowel risks splintering in my opinion (unless the dowel is too thick to crack, which I think would not look like tree trunks). As a person who has practiced archery with wooden shafts for the last 15 years, I am well acquainted with the strengths of wooden dowel. If you are really that concerned about litigation I'd suggest making all your scenery out of rubber, as metal or plastic houses, bridges etc can splinter and cause injury of someone 'leans' on them.
Basically, as I said, it was just a suggestion. I have had enough dealings with the vagaries of US law to understand that for you guys it's on a state by state basis a lot of the time, and what may be fine in one state is not fine just over the border. If the idea works for you, great. If it inspires something else, great. If it doesn't work for you or you don't trust the idea, that's also fine by me. BTW, I don't game on the floor any more, and I don't game with kids, so my risks are much lower that anyone will fall on anything. Bigger risk is tripping over the dog...