Hello everyone! Do I need pillar/dowel support if I want to put a single layer 6" round (2 inches) on top of a 2 layer 8" round (4 inches) ? 

AI wouldn't use dowels for 6 inch cake unless I was using a heavy cake topper

AI would and do. You can never be too careful with stacked cake construction.

AI would support the 6" tier. The rule of thumb is support every 4 vertical inches.

AThank you... I went ahead and used pillars. It turned out great!