"Star Wars: The Force Awakens" built a similar forest set. The foreground tree trunks don't need a canopy of branches and leaves above, leaving more room for light to get through.
That's the main problem with real forests, blockage from branches and leaves when the light is above them, or getting a lighting balloon punctured by a tree branch. So the trick if you have to use a real forest is to really scout for the best configuration, you almost want a field right in front of a row of trees to light the foreground action against trees, and then just a few rows of trees with another field or road running behind that to put up any backlight or higher top light for the background.
But essentially you are talking about a lot of soft top light.
Now if there are a lot of tree branches in the way, the other thing I've done is use them to clamp Kinoflos to them pointing down, slightly angled as a toppy backlight. I've also run a string of paper lanterns through a forest path, you can use daylight LED bulbs in them for a blue color cast. But that only works on tighter shots, for a bigger wide shot you'd need a larger softlight and then again you are talking about balloons or building a "moon box", a 20'x20' or larger frame of diffusion with lights behind it (Skypanels are useful since you can shift the color and dim them easily, but I've also used Kinos like Image 80's behind the diffusion.
Or if you have the right space, a big white bounce frame hung over the area, 20'x20' and larger, and bouncing into them from the ground. That only works for foreground when you have the space to work, back behind a row of trees you'd probably have to use a diffused light source hanging from a condor or construction crane.