YOu may have this problem: http://www.mapcore.org/topic/15556-udk-foliage-lighting-woes/ It is quite bugged, unless that has been fixed in the latest UDK. Last time I tried it was still broken. 128 is not a good idea for foliage, as it needs to get all lightmaps from each foliage cluster (default 100 instances per cluster)…