You know I think there is a much bigger problem with this mulching that wasn’t addressed: hydrophobic mulch. When you pile it on that thick it can become hydrophobic where it forms a waxy layer on top that water can’t even penetrate. Bark mulch shouldn’t be any thicker than 1-2”. Straw, manure, compost can be thicker but that looks like bark mulch in the video to me

Interesting point, but I largely agree with the top comments in that thread—this study doesn’t constitute strong enough evidence to demonstrate much definitively. It certainly suggests a need for further research.

Personally I have had questions about the conventional mulching methods. Many arborists insist that there must be a lot of space between the mulch and the trunk—I’ve sometimes seen as much as 6 inches recommended. My concern is that for a small tree, this constitutes most of the root ball, and you may be giving up on much of the benefits of mulch if you follow these instructions.

Additionally, if there is a big space against the trunk, it creates space for weeds to grow. In a well maintained tree this is a minor issue—simply remove them by hand. But most trees are non well maintained, and many landscapers will use a weed-whacker to solve this problem, which is far more dangerous to a young tree than a bit of excess mulch. In my experience, this type of lawn equipment damage is one of the most common causes of death in young trees.