Try using more then 1 tree variation.
A forest that has the same type of tree everywhere is simply not a forest.
Also, you might want to cover up the root of the trees with things like grass, flowers etc.
Why? Lets take for example a cliff:
Have you seen lots of cliffs that have a lot of trees on the very edge where rock starts to form?
(I'm not saying that it's impossible since it's not), but then how can the tree only have 1 root which is the bark?
Since clearly a tree can not live on rocks and the bark seems to be quite deep if it where like that in real life.
Unless the cliff exists entirely of grass and only has rock on the edge I think this would be quite impossible for a tree to live there.
Get my point
?
Hint: There are some really, really usefull tree doodads in the Ultimate Terraining Map including some with great looking roots.
If you really want to use this type of tree it might even be possible extracting these roots from the tree inside UTM and put it on the tree that you're using.
Tip: Take a look at real life forests.
There are still lots of things to improve to give it a more realistic view.
A few examples:
Pitch and Roll Variation of the trees. (Not all the trees in a forest stand exactly 90 degrees vertically)
There is not one bark of a dead tree lying on the ground?
I would say, get some leaves in there too.
Try to put in some more grass with more variation.
Take a look at some forrest pictures on google for some inspiration.
Want to make an awesome terrain? Use custom models and textures!
Here are some helpfull links which might be usefull to you:
http://www.hiveworkshop.com/forums/terrain-board-267/ultimate-terraining-map-3-0-a-45316/
http://www.hiveworkshop.com/forums/...e-terraining-hives-terraining-section-184427/
Also, it might be better posting things like this over here instead:
http://www.hiveworkshop.com/forums/terrain-board-267/
Since World Editor Help Zone is actually meant to help people out with their problems with the world editor.
Asking for guidelines, critique or anything like that on your terrain is better to be done in the terrain board.
Not only because it's the apropriate section but also because all the terraining pro's can be found there
I hope this post was of any help.
I didn't mean to invoke any negativity towards you or your creation if this is how you might've interpreted it.