Trees have black boxes around them

This happens when Cycles doesn't have enough transparency bounces set, and so once a ray goes through a certain number of transparent layers, it just colours that pixel black instead of continuing to the final surface.

To fix it, go to the Render tab in the properties editor, then go to "Light Paths" > "Max Bounces" > "Transparent" and turn it up to something like 30 (higher values will raise render times). This happens automatically when scattering with Alpha Trees, but not with Scatter5.

Panoramas render cut off parts of the trees

EDIT: This has been fixed for all version after v2.3, so if you still get this issue, please download the latest version to fix it. Note that it will only apply to new projects, so using the new version with an existing project won't fix it there. You can also follow the workaround below for earlier versions and existing projects:

This can be fixed by going to the material settings and changing "Fade distance" to 0 and "Fade speed" to 10.

These settings control how the trees will fade out when the camera gets too close to them, but it goes wrong when the camera is panoramic, and instead causes this problem.