By "filling environment" at this point, i only meant adding simple low poly trees to the terrain editor so i could get an idea of the random placement and how dense i should make the area look. All the trees are the same height in these pics but i adjusted them to be more varied using the min and max values within the deco layer settings. Leaves will be added later and should change the look of the scene entirely.
While working UDK i was messing with my dominant directional light, enabling light shafts so i can hopfully get good light coming through tree leaves. I also changed the colour of light shafts to be a warm glowy orange because when i eventually make my skydome and sun disc, i want the time of day to be when the sun begins to set. With this, i can display sunlight but also a mild darkness around the scene. This may change depending on outcome so i will see.
I added an exponential height fog just to cover the scene in a earthy colour toned surrounding until i make my skydome.