For example, you're standing in area where you just harvested Katryx Ore. There is a way to make the resource reappear (with all defeated enemies, but it's side-effect) quickly. For this, open your skilltree and then go back (you don't need to change anything, just open skilltree and then leave it). Then go to harvest the resource. Repeat until you have enough of said resource.
Among other things, this trick works with Orangium and Wild Dispel Herb (near Ebron.)