"On complexity levels 2-5, there is a chance that you will receive 50% less XP for mining, fishing, woodcutting, farming or thieving certain resources (the majority of resources in a dungeon will give you full XP). These resources are placed in lower complexity dungeons so that you can get used to how the skill works before moving on to higher complexities; as such, we did not intend them to be power-trained on for XP, and we have lowered their XP rates accordingly." http://www.runescape.com/kbase/guid/dungeoneering_faq