Living and nonliving systems - weather - constantly
interact and adjust to each other. Again, in a sense, they are like a pump
or seesaw and the rules of dynamic equilibrium and dynamic oscillation are
effective. They appear in balance only because we find it difficult to
perceive the constant changes that take place between two systems. We know
that the environment [En] can effect living systems. And, we have seen in
our time how living systems can effect the environment - cut all the trees, and
clouds that bring rain begin to decrease, and drought begins. I see the
host [H] and parasite [P] as interacting systems for the benefit of each so they
can survive against the pressures on an ever-changing environment.
When a host system or its parts cannot maintain order because of decreasing
energy, then another system - parasites, pathogens - begin to use the energy at
lower amounts to maintain order in their system. The energy that comes
into living systems will be used. When we think of pumps or seesaws,
dynamic equilibrium and dynamic oscillation, and energy to maintain order, the
subject becomes very simple and very clear (For more information see Tippett, J.
T. and A. L. Shigo. 1981. Barrier zone formation: A mechanism of tree defense
against vascular pathogens. IAWA Bull. Vol 2: 163-168).
SOURCE: Page 206 and Page 207 from MODERN ARBORICULTURE by DR SHIGO.