think you are confusing terms.
Young tree training is very specific.
Crown cleaning is an attempt to remove unproductive growth, poor contributors, reduncies etc. Dirty? why are going there? Timing, crown raising? We know tons of shit about pruning. Is it all in one place? No? Couple of good books, local pros, horticulture and botanical gdn resources, European resources are great.
Pruning standards are what? A place to start, for who? For the inesperienced, uneducated etc. It is not an authority by any stretch of the imagination.
Just add there is nothing wrong with a clean tree. Allowing light and air to penetrate a crown can help strengthen trees/cell growth/produce photosynthates. Limb wood is photosynthetic. Its like a big LEAF.
And like a leaf, they can shut down. Maybe that is why SLD occurrs. |Just thinking a loud at this point| sorry for the distraction. You heard it hear 1st