Working with the foliage tool, I've discovered that there are quite a few options to change the placement of the vegetation including an offset Z value to place them at a different height on the ground each to add variation, but there is missing a similar option to place trees with a randomized rotation offset. You can see it in this picture clearly. Every alder tree is placed in the same direction, with the pattern of each tree facing the same spot. The only thing which makes them look different is the Z offset option which alters the height of the trees being placed on the ground, and which I maxed up to 100. I really would wish an option to randomize the rotation of vegetation when using the paint tool, because it can be a bit boring facing the same tree type always from the same direction. I mean I could select each or a few of these and alter the rotation of it later on, but imagine if the radius/size of the paint tool is very big and painting a forest for example, editing the rotation of single trees in this way would take years to complete and is simply not worth it.
I won't have a chance to test this out myself until this evening, but does it let you select a blueprint actor as the tree? Then I think you could add a rotation in the construction script fairly easily. Not sure if that's on the right track (as they say,) that's just off the top of my head. Edit: never mind that nonsense; looked it up just now and I think fceschmidt has the right idea.
Yes, that was it. How embarassing. I tried this option before, but together with the Random Pitch Angle parameter below, which kind of makes a yaw at the vertical axis and was absolutely not what I wanted, so I thought it would be kind of an activator for that. *facepalm*
matinakbary - another one for the documentation - how to place vegetation assets with random rotation.
No reason to be embarrassed Yaw, pitch and roll are kind of special niche terms for rotation around the z, y and x axis respectively. I also didn't know about those words before trying flight simulation a couple of years ago.