Problems which arise from the environment and not caused by living things such as insects or diseases are called abiotic. Soil compaction, Air pollution, Nutrient deficiencies are examples of Abiotic factors.
A big part of plant health care is to provide trees with the nutrients and compounds they need to metabolize and grow. In the past a great deal of emphasis was placed on the element Nitrogen. As it tends to move through the root zone of plants easily, it is often in short supply. Nitrogen makes green leaves greener and promotes growth. The more research which is done on tree fertilization the more the realization that Nitrogen may not be the answer for old trees and those that are in trouble.
The new "breed" of fertilizers for tree rely on biostimulants which feed microorganisms in the soil, the vitamin B complex which stimulates roots and enzymes which stimulate plant metabolism.
Plant Growth Regulators
Paclobutrazol was originally developed as a fungicide. It inhibits the development of a plant hormone know as Gibberellin which controls shoot elongation in plants. It was thus developed as a plant growth regulator for the line clearing industry. A little more study revealed that if the plant was no longer producing Gibberellins then it had additional resources it could use for other things such as more chlorophyll, more roots, and more defense compounds.
A tree treated with Pacloburazol has smaller thicker greener leaves, greater production of feeder roots and more leaf hairs. In addition to merely limiting the growth of trees, stressed trees can be treated with Paclobutrazol to improve chances for recovery and survival. Trees damaged by construction are good candidates for paclobutrazol. A very useful tool for the Arborist. It is marketed under several labels: Cambistat, Profile and Shortstop.