Moving up (literally) from the grass and undergrowth comes the trees. I had in stock a pack of Woodland Scenics tree "armatures", which could be considered as flat-pack trees as the plastic moulding is completely flat.
The idea is they are twisted and bent into a three-dimensional tree. I found dunking them in hot water for a minute or so made that a little easier, and it was helpful to hold the trunk below where I was bending with a pair of pliers, but the concept works well.
The result is surprisingly effective. The best technique is twisting the trunk working up the tree, which spreads the branches in all directions, but as some trees were to be against the backscene they needed the branches bending towards the front or sides, away from the back. With a little thought the branches can fill the 3-D shape in a balanced way.
I then painted the plastic as it looked a bit, shiny plastic. I used a dark brown enamel wash dry-brushed with a mid-grey, and although at a distance it doesn't look that different it does take away that plastic look.
I used commercial foliage products - Woodland Scenics on two of the trees, and Heiki on the other. This is cut into small irregular chunks and teased out - particularly pulling the top and bottom of the flat material out to form more 3-dimensional shapes. I stuck the now fluffy foliage to the branches using matt medium ("Modge Podge" matt) rather than PVA, which dries invisible.
The trunks have a small peg protruding from the base, the idea being they can plug into a moulded "root" base to stick on a flat board. Of course I want to plant them into the ground, but the short peg wasn't enough to secure them, so I drilled a 1mm hole into the end of the peg and super-glued in a length of wire (straightened paperclip).
Here's the two at the back of the layout, with a nice open feel to them, and a good shape and size. On the left I've used a couple of the trees my son made for a school project using twigs and rubberised horsehair stuck on with hot glue. The best ones were used for Slugworth & Co., but these were revitalised with extra flock and planted in the corner, which they fill quite nicely. Just visible on the far right is a commercial tree I found in stock - it's a bit of a "lollipop" but fills a gap and isn't very visible!
The other tree sits front and centre, creating a view block - not least to hide the fiddle yard exit, as seen here - and to make the middle of the layout feel less empty. However, whether it is too much in the way remains to be seen! It could make operating tricky by blocking the view of the uncoupling magnets, so for now it is pushed into the hole but not glued.