For more information and comparison screenshots, please see this forum thread:
From what can be seen, the lighting conditions vary somewhat between the Arma 2 maps and Arma 3. Stratis is significantly darker when under a full overcast. In fact, it's still very dark even when partly overcast which looks odd. The level of light coming through of course affects the depth of trees due to lack of shadow contrast but even when in daylight, the mid-level trees are still flat as seen in the third Stratis screenshot. This isn't the case with Arma 2 trees which are textured as such to appear full at a distance.
Real world example: