Coverage can remove half or more of a tree's leaves. Since leaves are a tree's food factory, losing so many can make the tree hungry. Desperate to replace its leaves, a tree responds to cover with a flurry of new, weak shoots. It is highly recommended to cut only 20% or less of the top of the tree at once to prevent it from suffering.
However, there is an infamous pruning shortcut that prevents trees from living a healthy life. When you cut the top of a tree, you leave behind a weak tree that is unstable and at risk of decay. Observing where new branches sprout from the main branches and cutting in the right place, using the right technique will do much more to protect the health and promote the proper and future growth of any tree. However, everything is possible if the cuts were severe or if they were made in a way that damaged the tree's resilience.
The new growth that rises rapidly from the dormant buds just below each cut is only anchored in the outermost layers of the mother branch. Branches that are about to die or that are already dead should definitely be cut off, as well as those that are decaying, to prevent decay from spreading to the rest of the tree. Slowly dive into the top of the tree by starting to cut the smaller branches before moving on to the larger ones. As long as you're willing to deal with the potential loss of these trees if you continue to keep them cut to between 20 and 25 feet, that's the worst-case scenario.
Finally, save only 1 to 3 shoots in total from each previous cover cut for the best chance of restoring strong leaders and branches with good structure. As a defensive action, the hungry tree responds by quickly sending multiple dormant bud buds below each cut. In answer to this and your other question, cutting off bushy growth won't help promote growth to the top, unfortunately. However, cutting them down will likely produce new growth, but this new growth will be much weaker than the original wood.
I have a walnut tree that attracts crows, I would like to cut it shorter so I can put a net over it to keep crows away. When proper pruning cuts are made (just beyond the neck of a branch at the junction point of the branch), healthy trees are genetically equipped to close the wound. If you don't like the bushy look of the new branches below, you can cut them off, but you'll see that, in a short time, you'll have more new growth around the area of the branches you just removed (the new bushy growth area).Sunshine Coast Arborist Tree Service
89 Little Mountain Dr, Little Mountain QLD 4551, Australia
1800 951 221