Trees have been glued into place with a cheap epoxy resin from Poundland. I use this for most of my basing work - it takes a bit longer to set than Araldite Rapid, but when all I'm doing is sticking people onto washers or slottabases this doesn't matter. More dried tea-leaf "leaf litter" has been added to conceal the bases of the trees, followed by some static grass around the edges so it will match the gaming boards we use.
I've added the odd extra clump of grass here and there on the leaf litter, plus a small bush or two (woodland scenics clump foliage).
I think I'll add a few more bushes, perhaps some reindeer moss too. I want to leave enough space for Flames of War bases though. I'll take this small copse to the games club next time I go and see how it looks. After that I'll carry on with the other 9 bases!