What is this 90-3-90 rule that I found on a certification test I took recently ? The multiple answer I used was that 90% of the tree's crown could be reduced by removing 3 branches. Is this correct? I can not find this rule in the ISA Certification Study Guide. Please help.

Reply to post by John Fischbach, on April 25, 2000 at 13:05:56:

John, I hope the test went well. All of the questions on the certification test aren't covered in the study guide. Others come are drawn from the books listed in the guide as suggested reading. You can find the 90-3-90 concept on page 18 of Shigo's book, Pruning Trees Near Electric Utility Lines, commonly known as The Little Yellow Book. I think it may be in Modern Arboriculture also. Anyway, it reads: "90 percent of the time, 3 branches can be removed to provide 90 percent of the clearance."

Take care,
Tom
Keep looking up

Reply to post by Tom Watson, on April 25, 2000 at 13:05:56:


Thanks for the clarification, Tom. We always have to guard against distortions or misunderstandings.

But actually, you can certainly adopt a 100-3-100 rule which would be to ALWAYS remove 3 branches to provide 100% clearance as long as one of the branches is the trunk.


Bob

Reply to post by John Fischbach, on April 25, 2000 at 13:05:56:

When I took a class that Alex taught he said it this way:

Ninety percent of the time, three cuts will complete ninety percent of any job.

When I apply this rule, I look at several parts of the job. I start with the whole tree. Which three cuts will I HAVE to make. Then I look at each branch or area of the crown. If I HAVE to take out a limb I make the decision just like I am given three coupons to cash in. This does not mean that any of the cuts are large or a large percentage of the crown is removed. A cut is a cut. Most times, the only live wood that comes out is growth that is a hazard of some sort.

Tom

Reply to post by Tom Dunlap, on April 25, 2000 at 13:05:56:

Tom, how would you suggest that I apply the three-coupon approach when pruning a large, multi-leader water oak about 80' tall with a 50' spread? With the rush of people moving back into Atlanta's old intown neighborhoods and renovating neglected houses, I'm pruning many of these, some that appear to have never been pruned. Their canopies are thick with crossing and inward-growing water sprouts grown into limbs. I basically work leader by leader as I move through the tree. I'm careful to remove only as much as I think the tree can tolerate in a first-phase pruning. In this case, am I allowed three coupons per leader? What do you think.

And while on the subject of crown cleaning, John Ball raises an interesting point in an article in the current Arborist News. In "Managing the Feature Tree," he questions the notion that crown thinning is good for all trees, noting that sugar maples and beeches photosynthesize efficiently at low light levels. This underscores another Shigo assertion - "Trying to treat a tree you do not understand is like trying to start a Rolls Royce with a sledge hammer."

Tom
Keep looking up!