This is a known issue with some AMD cards, and it seems something with tree rendering is causing it.
To confirm please edit world.cfg and set trees = false there.
Alternatively, it was observed that setting MSAA ≥ 8 or 4 helps too (no idea why, but it's a driver problem). You can edit eng.cfg and change msaa = 8 there. Please let us know if any of these helped, as we need a reliable test case for reporting it to AMD.