4 questions machine-gunned; shoulda looked at your sig line about Reactions!
Internodal sprouting is not as stable or efficient as sprouting at nodes, from what I've observed in oaks anyway. Nodal sprouting at or near the cut promotes closure and lessens decay; typically a good thing for the tree.
Retrenchment first referred to retreating soldiers finding a line they could defend, and digging in to fight anew. This concept relates very well to declining trees, so “Before cutting any branches to reduce the size of the canopy, visualize the new canopy outline. The objective is to make reduction cuts so that branch tips are left intact on the new, smaller canopy…Sometimes as little as a 3 to 6 feet (1-2m) reduction in height can add a great amount of stability to a large tree”, for trees with strength loss at the base. This effect is confirmed by thousands of Tree Statics tests in Europe and, recently, in North America.
Older trees strain to pull water to their periphery: “Water and minerals are transported tangentially through intervascular pitting, vessel distribution and vessel diameter. Movement of water and nutrients through pathways is affected by pressure; pits will close if pressure drops”.
Retrenchment makes more water available and redirects growth to a lower, consolidated crown. This pruning also redirects hormonal growth regulation, often resulting in reiteration and rejuvenation. This process has been likened to a king being overthrown, allowing the rise of several dukes and earls.
Reiteration is any shoot that repeats the basic form of the tree. Like new stems arising from stumps, reiterations in the crown are often extremely vigorous, so they make logical targets to cut a branch back to. However, when they arise perpendicular to the parent branch, their structural stability may be compromised. Cuts at right angles can also result in a “hollow elbow” type of decay, so cutting at the next good node may be better.
A reduction in diameter indicating a node can be felt more than seen, so running both hands along the branch is a vital step in understanding what to do with it. Dr. Shigo’s mantra, “Trees must be touched to be understood,” is too often forgotten today. Trees are living entities, so we can feel for more than form with our manual examination.
Repairing internal function is the goal of our work with damaged trees; restored shape is just a sign of renewed health. Form follows function, as other artists know. What other signs of tree health can we sense, to guide our work? Thermal images show concentrations of heat in trees, which may indicate internal functioning.
Rejuvenation of a tree’s physiology slows down, or even reverses, its aging clock. This is best seen in trees that grow on stressful environments, like mountaintops. Among trees, adversity promotes longevity. Damage can enhance dignity. "Pruning does it by inducing the growth of younger meristems, shortening the internal transport path, and balancing shoot load and activity with limited root activity and support. In trees, physiological and developmental aging operate independently. They can be simultaneously embryonic and senile, resulting in a form of ecological immortality. It is this potential for immortality that makes trees so fascinating to work with."
OK?