Lets not forget about the mistaken tendancy to lump all branches into the tree model, with larger tree species each large developed limb needs to be treated as an autonimous unit...ie I would not be very happy removing more than 25% of live foliage from any single limb structure (without good cause and sound reasoning) knowing that to do so will dramatically impact on the apical control operating within that limb.
For me this is where experience and knowing the species you are working on comes to the fore. A very great many Euc species have very sparse live foliage held far out on the ends of the limbs, almost naturally lions taiiled! Reduction/thinning etc is a real art with these trees...if you remove too much live foliage from the limb you will predispose that section of the tree to epicormic flushes, weakened chemical and physical defences...great care and consideration is needed...know why you are cutting and what the likely consequences will be.
One more oint try always to impress on clients the inportance of improving the soil root environment...yes they might be focussed soley on the leaves branches the stuff they can see...but we all know (I hope
) that the real deal is in the ground. Keep the soil and roots healthy and thriving and you can have greater fllexibility up top with reductions/thinning etc...
BTW branch autonomy is kind of fascinating Coder has a little bit about it in his papers on chemical messaging in tree systems.
Growth control systems.pdf Tree growth response systems.pdf Control of shoot root balance.pdf