[College of ACES] [University of Illinois] [Illinois CES]

Re: Fundamental Arborcultural Assumptions

schrader@beaches.net
Sat, 12 Oct 1996 15:24:17 -0500

Your question.
Is there any statistically valid data supporting the thinning of healthy shade trees in order to reduce the "wind resistence" of the plant?
Answer.
In of my own experience. I aggresively performed ( HURRICANE PRUNING ) In Miami, Fl. . for the six years preceeding Hurricane Andrew with great success. Of 1500 clients I had one who experienced a loss. The rest where only minor breaks of small branches.
Understand: Pruning for wind resistance is not solely diminishing canopy. I would term it more as directional pruning. One guides the developement of a tree into a form that relieves and distributes wind stress. Even mature trees are constantly expanding their canopy areas.

Your statement.
However, a tree is a three dimensional living organism which has developed its growth form partially in response to wind vectors.

I understand sinker roots are developed in response to wind stresses. I have noticed little response in upper canopy form however. Could you be more specific? What is a wind vector?

Your question. How can the removal of living material that is still photosynthticly productive be of benefit to a healthy, mature tree?
One cannot continually remove leaf canopy for the sake of diminishing wind stress with out reducing the trees ability to produce food.
We humanes sometimes want unnatural things from trees. In nature a tree is successfull if it lives long enouph to reproduce. We want them to be attractive, safe, and long lived. Surprisingly, the average lifespan of a tree is relatively short when compared to their ability of an indefinite life span. Obviously expanding that life span falls with in our interest and pruning is used to correct and encourage reliable forms of canopy expansion.

Since a trees Life Span is directly related to its ability to withstand wind and weight stresses. Preventing the loss of a limb prevents the formation of decays associated wth limb losses and is a vitaly important part of keeping a tree healthy and strong. Each limb is responsible for its own food production, ( its leaves ). Manageing the canopy so that each limb possesses its own sunlight area to develope in will prevent limb loss.

Your question.
Have there ever been any engineering studies done on the proper placement of cabling systems within shade trees? Could not the improper placement of such a system actually increase the risk of branch failure?

Answer.
I don't know about engineering studies. Trees distribute stess by bending. Cableing restricts this movement and does cause failures to occure in those fixed points. Correctly applied cables are placed in the upper 1/3 of the canopy where the cabled stems are allowed to flex together as a unit. I do not think it is wise to bore thru the stems when installing cables. Boring creates decay. Using a slack cable and wide straps makes more sense to me. Cables and straps do need to be inspected, adjusted, and moved periodicaly.

My question.
Would you please explain how trees develop their individual growth habit partially in response to wind vectors.

George Schrader
American Tree Experts
ISA certified arborist SO-0448
904 769 4060
schrader@beaches.net