I know that's what you believe and what you teach but I have been using Pine bark in a soil mix for more than 50 years. If you have the correct percentage of grit and nothing else breaks down the bark is not an issue in my opinion. However if you mix products that decompose and break down like some of the clay substitutes and mix it with Pine bark you could have a problem.
Well, I base a lot of my opinion upon what I've experienced teaching repotting classes. For about 5 years now, I've been teaching repotting classes, and people bring in their own trees for the workshop. Many of these trees had never been repotted since they purchased them. Many of them were at one time trees originating from Brussel's. Some domestic, some imported. Many were in Brussel's pots.
Brussels uses composted pine bark, sand, and peat on their "ordinary" trees. Maybe some pumice is added to the more expensive ones. Azaleas, thank goodness, are now potted in Kanuma.
But, I have found more root rot and dead roots in Brussel's soil than any other Mix. (Potting soil, excluded).
Whenever I encounter a tree originating from Brussel's my first advice is to get it in better soil.
I have also purchased two trees from Julian Adams, that were grown in 100% Turface. What I have found is the roots in both of them were a thick pad on the bottom, but nothing really in the body of the soil. It's like the roots are running to the sides of the pot, hit the walls, and then spread across the bottom. Rather than populating the Turface. Dav4 has mentioned that when he repotted his Rocky Mountain Juniper that he used to have in mostly Turface, when he lifted the tree, he would have long roots, but not a firm root ball. All the Turface would fall away. That's because the roots aren't growing into it.
Pine bark and Turface are shaped poorly. They're both rather flat. So over time, the soil mix compacts. Think of a jar full of pennies. The pennies lay flat. There little air space in the jar. Now think of a jar of marbles. Marbles being round, they leave a lot of are space between themselves.
Air is crucial for a healthy root system. When we water, the column of water flows down through the open spaces between soil particles. As it descends and drains out the bottom, air is pulled down from to surface to take its place. If the space between particles is tight, little fresh air is brought in. Compacted soil without fresh are turns toxic because anaerobic bacteria and molds start to grow. These don't need oxygen. These cause the root rot. They will only grow where there is a lack of oxygen.
So...
Many people use organic s in their soil mix because they think the tree needs the "nutrition" provided by the organic. Not so. We can deliver the nutrition the tree needs with fertilizer.
Think about this: what is one of the most lush vegetation places on Earth? Hawaii, right? Hawaii is all volcanic. When the first seeds arrived there, there was no organic soil. Only lava and pumice. Obviously, plants grew. Without organic soil. Without fertilizer, even!
