Hello, all.

I'm often asked how close can we cut roots, how close can we install a sidewalk, etc. I recently posted the following reply to a newsgroup. I'd welcome any comments and suggestions that might improve my future answers.

Unfortunately, there is no clear answer to this question (well, either
of them). Trees make energy through photosynthesis and store it as
starch and sugar. The stored reserves are used when the photosynthates
aren't meeting current needs. Current needs vary from tree to tree,
from species to species, from site to site, from season to season, from
year to year. As we have been through several years of summer droughts,
including last year's particularly severe one, most trees have been
calling on reserves more than they might in wetter years. That depleted
the stored supplies somewhat. If the trees had supplemental irrigation,
they might have suffered from this less than greenbelt trees or
non-irrigated yard trees (but if the irrigation was frequent and
shallow, the grass might have sucked it all up before it ever reached
the tree roots). If there was a lot of nitrogen dumped on them, they
would have put on a lot more leaf growth, which put a larger demand on
maintenance, leaving less for defense and recovery. If a tree was
attacked by a vigorous insect population, mistletoe, or some other
destructive agent, it may have tapped further into reserves. If the
soil is very compacted, roots may be struggling already, so cutting them
or piling gravel on top (exacerbating compaction as well as inhibiting
gas exchange) could cause further depletion.

What this means in terms of your questions is that some trees will be
better prepared than others to deal with the abuses described. A
healthy tree might not show any signs of damage at all, but one that was
almost out of stored food might die outright. Most likely is some level
of dieback but ultimate survival of the tree. In a greenbelt, the soil
is probably better (more organic material, less compaction, lots of
mulch), so the trees might survive nicely (assuming the gravel is
eventually moved off the root zone). In your front yard, which is
probably compacted and full of competing turf, it might come down to how
well the tree has been irrigated for the past few summers.

How close is too close to cut roots? That question will likely get five
different answers from any three different arborists you ask. Again,
part of it depends on the above-described factors. It's important to
note that most trees grow a wide, spreading mat of roots, not a deep,
penetrating system. Most of the feeder roots are in the top twelve to
eighteen inches of soil (higher in compacted soil) and extend tow to
three time the height of the tree from its trunk. If you picture that
circle of roots, then look at where the sidewalk cuts across it, you can
see that a cut that passes close to the trunk removes nearly half the
root system. This has implications on stability as well as
survivablilty.

One final thing: When a tree suffers severe root damage, it normally
doesn't show up in the crown right away (a function of the food-storage
process described above). So, if a contractor tells you he's been
cutting roots that close for 20 years and never hurt a tree, he's
probably either lying or ignorant. Construction damage can show up as
branch dieback as much as 10 years after the fact. If you see branches
dying from the tips inward, construction is the likely cause. Low
branches dying is more often a naturat process related more to lack of
light penetration through the upper branches.

I know that's not really the answer you were hoping for, but it's more
accurate than any "foot per inch of diameter" type rule.

Good luck,

Keith Babberney

Reply to post by Keith Babberney, on April 01, 2001 at 16:39:34:

It is important for people to have a more accurate picture of the world below ground, including the world of tree roots and the soil fauna.
The physiology of trees and the functioning of their roots is a vague thing for many people.
Your statement about the shape and extent of the typical tree root space is probably opposed in most people's minds by images of tap roots and large deep main roots.
Also, because trees often absorb a large amount of abuse before the damage becomes apparent, it may be hard for them to associate current problems with past events, especially when the initial damage is covered up.
Out of sight, out of mind, they say.
I think it is important to establish the value and importance of the tree in place to the owner.
Then preservation can be related to something tangible.
If it is very valuable, then added cost of protection can be justified.
At the least, the owner should understand up front what to expect if the root system is damaged.
Sometimes the damage can be largely avoided simply by creating an expectation that certain activities be disallowed beneath the tree during construction.
I see that building contractors often take an uncaring attitude to the health of trees, and the damage they do is not done of necessity, but rather by convenience.

Reply to post by Mark Goodwin, on April 01, 2001 at 16:39:34:

Mark,

Thanks for the input. I agree that the builder/contractor who knows or cares what happens to trees on his jobsite is a rare bird indeed. I have had clients tell me about how careful the dozer operator was while in the vicinity of trees, but I've seen a lot more drivers who are obviously trying to show how fast they can go, consequences be damned.

I think there's a real potential for connecting with builders and teaching them teh right way to protect trees, but I've heard other arborists say the builders don't want to hear it. I think the problem is that there is no clear link to his shoddy practices and the damage that shows up years later. Perhaps the best way is to hook up with realtors--when the prospective homeowner insists on adequate tree protection (not just wrappint the trunk with chain link and 2X4's) teh builders will have to sit up and listen.

Keith

Reply to post by Keith, on April 03, 2001 at 13:54:31:

Arboricultural Site Supervision - no more and no less - conditions of planning consent!

Paul H.

Reply to post by Paul H, on April 03, 2001 at 18:54:15:

Paul, how would such supervision be carried out and by whom? I am thinking in particular of a large construction job taking 1 and 1/2 to 2 years. Who comes around to see what is going on for that long, and what would they charge? At the University they say that tree protections are now written into the contracts, but I see them ignored and abused just the same. I really am wondering how this is done successfully, and how much it adds to the cost of the job.

Reply to post by Mark Goodwin, on April 11, 2001 at 17:51:49:

Arboricultural Site Supervision is relatively new in the UK, however, a number of companies offer this service. To tie in the original development assessment or implication study, along with method statements and finally supervision, provides an integral part of the development/planning process. It generates interest from planning departments because site supervision of such sites is often difficult for them due to time and financial constraints. The general run of things is as follows:

· Field Study incorporating land survey and topographical survey.
· Architectural design and unit density including associated infrastructure.
· Draft of Arboricultural Implication Study (AIS) incorporating removal and remedial requirements, protective measures, replacement planting, Landscape Evolution etc.
· Conservation survey (often NJCC Phase I standard).
· Site meeting with planners, officials, government departments to discuss queries.
· Submission of AIS as part of the planning application.
· Planning conditions may be useful to encourage Arboricultural Method Statements and Arboricultural Site Supervision (ASS).

The successful applicant may well go with the ASS – this takes the burden away from planning departments and allows a Consulting Arboriculturist to oversee the site on a regular basis usually every 2 weeks, but generally monthly (it’s a case of snap shot).

The supervision also gives you the opportunity to meet and discuss the tree issues with the builders on site and point out the requirements of the conditions. You can also allay any fears from local residents by assuring them of your presence in looking after things on site. Cost of site supervision is immaterial given that the development may run into $millions, your job is to prevent hold ups and assure that your original tree protective measures remain in place for the duration of the construction period. Monthly reports are then sent to the governmental departments and developer. Cost for monthly visits for local development schemes we are involved in (some spanning 2-5 years are in the region of $200). There are many other areas involved in this type of work, but I could be here all night listing them.

Hope this helps

Paul H.

Reply to post by Paul H, on April 11, 2001 at 19:46:46:

>>Planning conditions may be useful to encourage
>>Arboricultural Method Statements and Arboricultural
>>Site Supervision (ASS).

I am having a great deal of trouble restrainingmyself here, but since this is a seriouse discussion on a topic that that I believ in I wont go down that road.

Reply to post by John Paul Sanborn, on April 12, 2001 at 15:44:50:

I understand the very road you talk about, its not always that simple, and difficult to adopt or enforce, although you need to drive your thoughts into words, a half finished sentence is about as useful as a chocolate tea cup!

Paul H.

Reply to post by Paul H, on April 12, 2001 at 21:42:33:

Further to Pauls valuable contribution, some UK local authorities do follow up and enforce arb. protective measures on development sites and have extremely effective systems for doing so.
I find it difficult to get consultants involved due to the developer not wanting to pay the bills. Its easier for me to go on site, I will have had the predevelopment meetings and been dealing with the application pre planning committee stage. I like to think that we work with developers, not against them.Pie in the sky?
Richard Nicholson

Reply to post by Richard Nicholson, on April 13, 2001 at 04:20:43:

It will take time to get the developers and other trades to look at us seriousely.

We just had some sewer put in at the club and the contractor trenched right across the rootplate of a monsterous American elm, 5 ft from the bole. Then got mad when when I voiced my concerns. (I was tactfull)

Reply to post by JPS, on May 17, 2001 at 12:28:49:

Was he mad because he thought he had already worked out his plans with someone "in charge" and didn't like to hear about concerns after the fact?
Do you suppose he doesn't believe that his methods around trees are as bad as you think they are?
Do you think he just doesn't care about the effects he has on trees, and that he's only looking at his bottom line?
Was he only doing what he was paid to do, in what he thought was the most direct and acceptable way?
Do you think he is capable of doing the same job in a more tree friendly way?
What did the person hiring him have to do with any of this?

Reply to post by Mark Goodwin, on May 17, 2001 at 18:00:59:

He took the most direct rout from new drain-tile to catch basin. As he has always done. It would have been simple to go 5 more feet out and then back into the drain.

The problem is that no mechanism was set up to consult with me. The Clum G.M. tells me he stopped the contractor and made him go out farther.

Maybe I will be able to educat him after we do the needed exploration to assess the damage/risk of windthrow.

I guesse now I will get authority to aprove any work done.

Reply to post by JPS, on May 20, 2001 at 22:31:41:

Good for you!
It sounds like you handled this in a professional manner and ended up with more respect.
There is a great gap between what is known in the profession and its implementation, when construction is arranged at a "higher level", but without involving the tree consultant in a meaningful way.

Reply to post by Richard Nicholson, on April 13, 2001 at 04:20:43:

In general Richard is right. Unfortunately, a number of private consultants do not give the planning authorities the data they need to fully assess the implications of the development proposals in relation to trees. And not just the tree, also included is any vegetation worthy of retention. However, the biggest problem is the site next to the one you are working on. Why is that one always exempt from all the hard work? For example, protective fencing on the floor, trees roots bulldozed, piles of spill around tree bases, lower branches snapped off from passing vehicles, footings for dwellings under tree canopies, cars parked within tree canopies, building materials stored abut tree stems, developers signs nailed to trees, trenching for utilities, etc… OK limited LPA budgets, but maladministration in the long term may cost more. It’s a wind up and often annoying.

In relation to planning submissions and any later conditions imposed - You cannot enforce for one without enforcing for all!!

Paul H.

Reply to post by Mark Goodwin, on May 23, 2001 at 17:31:04:

Even if your developers do take tree protection seriously and follow our recommendations what do we do when the issue is curb and sidewalk repair? Many of our old boulevard trees in inner city communities have curbs and sidewalks that are just as ancient and need repair for public safety. Are there new materials, methods and design solutions available, to minimize damage to roots of trees whose trunks are less than a meter from the curb and/or sidewalk? We would be able to implement these by including them in our municipal specifications but I would like to research what's new in the cement finishing trade. Anyone know?

Reply to post by Anita Schill, on May 24, 2001 at 18:59:33:

Heaving of walks is a problem in old sections of cites. Some studies show that most of it is not from th trees, but from poor engineering. But we all have seen the sidewalk being pushed up by a butress root that wants out of the narrow confine it exists in. The only thing that can be done in cases like this that wont damage the tree is to bring the walk into the citizens yard, or build a pier acrross the root area.

I have seen both, but more often the tree is sacrificed to expidiance and conformity.

Reply to post by JPS, on June 11, 2001 at 23:31:45:

Often construction is not done to repair damage from the trees - more often, the trees are innocent victims of roadwork, water and sewer crews making repairs and new installations with no real concern for the trees that are "in the way". We now are informed prior to excavations for some of these utilities but I would like to know of different options - do they have to excavate so deep and close to the tree roots to repair curbing? are there new materials and methods of curb repair that are less damaging? can sidewalks be raised up to avoid root damage? Any creative solutions and experiences?

Reply to post by JPS, on June 11, 2001 at 23:31:45:

That is quite interesting. My experiences have shown me virtually the opposite. The older sidewalks show less problems from heaving due to tree roots expanding beneath them. I figured it was related to the inability of the contractors back then to achieve the extent of compaction that they can now, thus leaving the soil better capable of absorbing root expansion.I really don't know the answers, according to Shigo, I probably don't know the right questions,

James.

Reply to post by James Causton, on June 14, 2001 at 17:52:11:

I guesse I was pointing this out as "the exception that makes the rule". Iwas refering to trees that are so large they are pushing the curb out on one side and the walk on the other.

Reply to post by Anita Schill, on June 14, 2001 at 17:52:11:

Check out Dr Kim Coder's approach to this question at ...

http://www.forestry.uga.edu/warnell/service/library/for98-011/

I put the root-plate radii and critical-rooting-area radii into an Excel chart, had it plot them on the Y-axis against tree diameter on the X-axis, and came up with a graph that's pretty easy to understand. Kim's explanations are good, too.