First time I set specular = 0 but crack and scratch were unvisible, then I set specular .01. I know that it should look not natural but effect was better. I think that I cannot work with lights. I checked google and I think that shiny shader looks like plastic imitation of bark on cheap IKEA furniture, but with 0 specular it looks even cheaper ;)

I like last GeneralNutt shader - right trunk. No shiny and does not look flat, but I think that shadows of leafs make it black.

Some time ago I wanted make more relistic pattern (I do not know, if any tree looks like this one). I tried make procedural material with 2d shaders, but it requred good UV mapping, then I gave up. Moreover I do not understand all description of optical physics, which I found in threads about shaders and I'm too old to learn it ;)