Having built my sci-fi Goldentrees park, I realized I needed more trees, because the rules I'm planning to use allow for two forested terrain types.
Rather than building larger bases with multiple trees, this time I'm going for individually based trees. This allows more flexibility on the tabletop, and will be easier to store.
This technique will work with any trees of this size.

These particular trees – which I previously previewed in their 'green' varsion – are a mix of 2½" and 3½" tall, and in my judgment, their wooden bases won't keep the trees erect if someone bumps the table or a window is opened on a windy day. So I'll be basing these on fender washers, which cost $0.25 USD each.

I've already sprayed the trees with matte clear to keep the golden sparkles from getting everywhere. (Not a perfect solution, but it helps.) Flip the washer so the 'rounded' edges are down, as any imperfections are usually on the other side. To get a good bond between the metal washers and the wooden bases, I'm using gap-filling superglue, which I apply to the washer and then press the tree into place.

After the glue dries, take a good look at the tree, straighten it out if needed, and prune off any problem branches (particularly at the top and bottom). I then apply spackle to get a sloped edge to the base.

Depending on what type of spackle you're using, it might shrink and need a second coat. I use a dull craft knife to scrape off any excess. I also flip the tree over and clean any spackle that's got onto the bottom, using a dull craft knife and a wet fingertip. Finally, I run a black Sharpie along the washer edge, as this seems to act like a primer, believe it or not. Then I apply a cheap brown craft paint to the trunk and base.

I let the paint dry, then apply some thinned-down white glue and dredge the base in a container of flock.

The tree is finished off with another spray of matte clear, to seal the flock in place (and help once again with the golden glitter!).

So, how many trees do you need? In the rules I'm using, the shelf liner marks the terrain, so technically I only need one tree to denote the terrain type. Looks a little bare, don't you think?

Four trees looks better. You could always class this as 'light woods'.

Eight trees looks good, but it's just a matter of taste. For a realistic look, put the larger trees in the middle.

Sixteen trees are obviously a thick woods. But with this many trees, it becomes a chore to move them out of the way when figures move into the terrain.

Twenty-five trees is about the maximum that will fit!

A Giant Scorpion is moving through the goldentrees, looking for invaders.