The Question: How do you determine the root zone of a tree?

When trying to estimate the root zone, what factors do you consider, and how do make your estimate? Is it based on dripline? Tree height (times some factor)? Trunk diameter?

Transplanting guidelines often quote 10 to 12 inches (250 to 300 cm) of root ball diameter for each inch (25 cm) of trunk caliper. But is this adequate for larger trees in the landscape?

Using dripline is just a "rule of thumb", and in many situations has no real bearing on the actual root zone. Forest-grown trees have systems that grow far beyond the narrow dripline, and wide-spreading trees may have a more confined root zone.

The point here is that in order to estimate what part of the crucial root zone is likely to be damaged by disturbances, we need to estimate where that crucial root zone is- how far it extends. Recognizing that each situation will differ depending on soil conditions, species, etc., what are your thoughts?

Reply to post by Russ Carlson, on August 28, 1999 at 00:53:20:

Gary Johnson (He has an article in this months Arborist News) taught me about the CRZ. To figure the zone, take the DBH in inches, multiply by 1.5 and you have the RADIUS, in feet, of the CRZ. Gary says taht if nothin happens within this zone, the tree can be quaranteed to live. The more of the diameter or quadrants of the CRZ taht is encroached upon, the more effect it will have on the tree.

Tom

Reply to post by Russ Carlson, on August 28, 1999 at 00:53:20:

Good question Russ. I had a table done up with three different "Rules of Thumb" for a course I taught but if the file still exists it's on a hard drive of another computer that's not set up right now. I'll try to summarize them:

1) The traditional DRIP LINE.

2) A 1:1 ratio of trunk diameter inch to protection radius foot (effectively 2 feet area diameter to 1" trunl diameter. Chuck Stewart who teaches the Trees & Construction course around the country for NADF uses this one. His 25 year experience has been a) that if this ratio is observed a high (??maybe 90%) survival/success rate is achieved. (I assume this is conditioned on a reasonably healthy tree selected to remain). A principal advantage he observes is that it's an easily checkable and usable quantity in the field by the tree list maker-upper, the surveyor, the contractor and so forth. There are no ambiguities about what or where drip line is.

3) A similar type ratio but with a more rational and detailed approach is set forth in Nelda (Matheny) Jim's (Clark) Trees and Development Table 6.2 page 74. It incorporates Species tolerance and age class (for specimens assumed to be of average to excellent vigor). It's drawn from the British Standards Institute 1991 BS 5837.

Clearly, the site history (drought, prior I&D, prior disturbance, etc.), topography, available rooting area, etc., etc. will further influence the size and shape of the critical area. Another big issue would be the time available for prepping the tree before impact and the likely level of aftercare to be provided.

I suppose there are all sorts of indicators of vigor including Shigometer (if you've got decent base line data), starch reserves, growth ring patterns and the price of chickens in Cleveland.

And I suppose how far one goes in making such investigations will depend on the level of interest in saving the tree (is it a key tree or are their other, better candidates?) the level and intensity of impact (first level of resource assessment) and the availability of computer diskettes in DesMoines.

Data are generally a good thing. Objectivity is desirable. But I suspect in the final analysis it must come down to good judgment based on good, locally applicable experience. The draftsperson can apply the textbook ratios to a print, but not look at the situation and make judgments. And some of the rules of thumb, if they incorporate informed experience, may indeed be very useful.

And it's more than SWAG. Informed intuition is more than a wild hunch. It's the sum of internalized experiences. I have some literature citations on that, but also filed away somewhere.

Reply to post by Tom Dunlap, on August 28, 1999 at 00:53:20:

OK, great. But that is Gary Johnson's definition of CRZ. Is that published elsewhere?

I ask because it does not correspond with the Root Plate Radius that Mattheck describes for structural support. We are looking at several different factors, so I just want to be sure we distinguish which is which.

Johnson's CRZ = DSH x 1.5 would seem to be a protection area for general health as well as structure. Guess I'll hunt up that article.

Reply to post by Scott Cullen, on August 28, 1999 at 00:53:20:

Thanks for the input, Scott. Most of those suggested models are the ones I'm most familiar with. The major point, with emphasis, is that the local arborist is probably (hopefully) best prepared to make the determination of what protection is needed.

Reply to post by Russ Carlson, on August 28, 1999 at 00:53:20:

Russ,

I have used the same figures as noted by others; DBH in inches converted to a radius in feet, however, I then consider wind exposure, lean, and slope. If I have to give somewhere, I will try to do it on the donwhill side, the lee side, or the underside of a leaning tree. In this way the rootsystem holding the tree against the wind, slope and lean is given greater preference.

Around here when I ran Horticulture, I would bargain with the construction contractor on utility corridors etc, and if they had to come into the CRA I would try to manage where, and then negotiate an equal amount of undisturbed area on the windward side, uphill side, or backside of a leaning tree. Sometimes got a bit dicey but once the contractor understood what the formula was, they often came up with the best location before the discussion began.

I have used the 1 foot to 1 inch rule on trees of minor value and the 1.5 foot figure for trees with scraggly rootsystems or high value.

Wayne

Reply to post by Wayne, on August 28, 1999 at 00:53:20:

I understand the process you describe, but you used an interesting word: negotiate. Often project managers, developers, lawyers will see a spec for root protection and immediately try to negotiate something less. Just as if they were negotiating an interest rate or job price. The first thing that must be pointed out to them is: the tree does not "understand" negotiation. The tree does not offest additional root loss because you promise to plant more bushes on another part of the site. We have rules of thumb. We can say relaibly "the more damage you do the greater the impact" so we try to minimize impact. Some other decision maker besides the arborist and untility contractor decides the importance of the tree (vs centrally supplied steam heat in the pool cabana) and the cost to be incurred to minimize impact. From that point on there is give and take and creative problem solving in minimizing impact while burying the steam line.

Reply to post by Scott, on September 03, 1999 at 09:55:46:

Ah! I forgot an important aspect of the "negotiation". I had control of the final payoff on the jobs. Our contracts provide for the "Owners Representative" to have work stoppage power throughout the jobsite, its accessways and egressways for the "protection of the gardens assets and living collections" The owners reps are then listed by name, title, phone number, fax number, beeper number, emergency number and radio call name. By golly if you screw up, you better get ahold of us! 10% of the contract price rides on "protecting the collections and assets" and on a 25 million dollar job thats alot of the profit.

Our experiance has been that it all has to be dealt with up front, above board, and with deadly seriousness. And the first violation of tree protection results in a site meeting, certified letter to the contractor pointing out the nature of the violation, meeting on site with the project manager and then when its all over, a cup of coffee with the foreman and backhoe operator and a casual conversation about what caused all the ruckus. The guy that saves the contractors contract is the foreman and the equipment operators, not the muckety mucks that sign the contract and get the letters.

We try to give them credit in the end for how great the finished job looks in its setting (the setting that caused them all the trouble in the first place)

Just some thoughts

Reply to post by Wayne, on September 03, 1999 at 11:35:28:

Well, that was a significant piece of the story. I like it: warn them up front, then kick _ _ _ and take names! All this needs to be in bid specs, not just contracts. That way they ALL know what they are bidding on. And the contract has to have real teeth. Penalties, retention not payable, work stops (time=money), bad PR, the more the merrier. Sounds like you have it covered.

Reply to post by Scott, on September 03, 1999 at 09:55:46:

Edward Abbey maintained that when dealing with nature, there is nos uch ting as compromise. Nature always looses. When the proposal is to put in a paved, two lane road into a natural area, people think they "won" when only a dirt road is put in. Wrong, you just lost less in the first negotiation. Out of these thoughts, Abbey came up with his slogan, and the basis for EarthFirst! "No compromise in the defense of Mother Earth."

RIP Ed!

Reply to post by Scott, on September 03, 1999 at 09:55:46:

AS Tom pointed out, you have already 'negotiated' a compromise, when you tell them to put it over there, not here. By allowing the work anywhere near a tree, it is affected and already compromised.

Reply to post by Russ Carlson, on September 03, 1999 at 11:35:28:

Yes, indeed. Anything more (in terms of impact) or less (in terms of undisturbed protected area) that status quo is a compromise of the tree's likely continuing performance.

I was specifically referring to the notion of a non-tree compromise or negotiation:

"I want to buy this car for $X that's all I will pay. my sales manager won't let it out of the show room for less than $Y, no way, no how. OK I guess I'll go to the other dealer, bye. No wait, no wait. What if I arrange for an all expense paid trip to Bear, De the garden spot of the East, that's a $Z value so for $Y you're really getting $Y + $Z, that's really like getting the car for $Y - $Z and that's even less than the $X you were willing to pay. Right? I think so don't you? But you have 30 seconds to decide because my sales manager leaves for Las Vegas for three weeks and he'll need to approve... better decide now (the imminent event close). Well you may buy this but you didn.t get a different car and you paid more.

Now a tree: "Well I can't possibly move the driveway further from this tree, the architect carefully sculpted the radius to play off the light and shadow playing off the building at the winter sostice, it's very cool. But what if I plant 2 dozen forsythia and three flowering crabapples over there next to the interstate?" You may buy this, and maybe you'll get the add-ons for no additional $, but the tree in question is not less damaged because of the offset.

The owners, developers, engineers, project managers don't always understand that "Let's Make a Deal" doesn't always accomplish the specific goal of tree protection. You need to explain that. It may well be there is no room for improvement re: the specific tree and if that's the case then some compromise which benefits the site as a whole may be a deal you want to take.

Reply to post by Scott, on September 05, 1999 at 22:43:45:

>> What if I arrange for an all expense paid trip to Bear, De the garden spot of the East<<

ROFLMAO!!!

The issue stillgoes back to the decision makers- who determines the worth (not necessarily value) of the tree and its benefits, and how much are they willing to give up for it.

If you had said the architect designed the radius of the drive to play off the shadows of the TREE instead of the building, then destroys the tree in the process, where is the benefit? Like a F.L Wright house with a tree in the living room that soon dies from the damage. Now what do you do with that space? Or a 40-foot square flower pot I designed in front of a commercial building to accomodate a 36 inch (female) Kentucky coffeetree? At least it is still doing well 13 years later. That cost the developer about $70,000 to keep that tree, plus lost parking spaces.

Reply to post by Russ Carlson, on September 06, 1999 at 08:00:15:

Yes, absolutely. The point is getting the decsion makers to undertsand which costs result in which benefits. $7,000 to build the planter for the CC tree led to its survival and continuing benefits stream. $X to contribute to the local library because it makes him look like a nice guy may pay off in PR and approvals but it didn't help that tree at all. So the planning board needs to know what benefits they want the guy to pay for.

Reply to post by Scott, on September 06, 1999 at 13:13:44:

You missed one decimal place- It was over Seventy Thousand dollars- They had to 'move' the building (redraw), reconfigure the entire 250-space parking lot, try to come up with 8 more spaces to meet code, and build a retainer wall 5 feet high around the tree (parking lot grade was 5 feet below original). Oh, and pay the arborist, too.

Reply to post by Russ Carlson, on September 06, 1999 at 15:12:04:

Oh, those pesky decimal places. And my abbreviation was off too. Kentucky Coffee Tree should be KC not CC.

Reply to post by Scott, on September 06, 1999 at 20:30:05:

And cofffeetree is one word, since we're getting picky

Reply to post by Russ Carlson, on September 06, 1999 at 08:00:15:


Of course, he could have spent even more and moved the tree,
retained the parking spaces, etc had the space been valuable enough.

Mark

Reply to post by Mark Hartley, on September 06, 1999 at 13:13:44:

The point here was not just to save the tree for its own sake, but rather to use it to enhance the front of the building. The building was 'moved' on the plans to center it by the tree.

The property management still gets questions on how they planted that large tree in the 'pot'.

Reply to post by Russ Carlson, on September 07, 1999 at 12:44:31:

But I really didn't know it was spelled with three f's.

Reply to post by Scott, on September 07, 1999 at 21:56:56:

Hey, I'm the webmaster... I can fix that!