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Wall Crumbling under Tree Question
<Chris reid>
I take care of a garden that abuts a property that has a tree that looks like a potential hazard to me, and I want to ask your opinion.

Picture a fairly short, steep slope -- I would say maybe 6 feet or so at about 45 degrees -- with soil that is a little unstable. A very old stone wall that's about 2 feet tall sits at the 6 foot mark, and a tree has grown over the top of the wall. The roots of the tree extend under a deck (about 6 foot clearance under it) farther up this hill, and the downhill side of the trunk flare actually sits on the wall.

The tree is definitely within target-shot of the building (my client's building) if it did fail.

Last year I had a major, well known tree company come in, look over the property, and do some work. I was concerned about this tree last year, and explained my concern that maybe the wall's deterioration meant the tree had less support. The arborist who made the sales call said it was not a problem; he seemed to think the tree was not unstable.

Well, I just visited the place for the first time since last fall, and stones are even more displaced out of the wall than they were a year ago. Don't know why it's moving -- erosion? freeze thaw? tree growth in some way? I thought the tree looked like it was blowing kind of jerkily in the breeze, but it was fairly subtle and maybe I'm wrong.

The tree is of moderate size -- I would say maybe 20 feet tall(?). I am wondering if it is more likely to be uprooted as these stones shift under the edge, and also if there's any possibility of the tree kind of bouncing and the roots' shearing, leaving the root mass in the soil and having the tree fall over in high wind.

I am going to recommend they have an arborist go to the site and put his recommendation in writing (easier to talk to the homeowner --or the insurance company -- that way), but wanted your input on what you have seen and whether this sounds like a bad situation or not.
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<Russ Carlson>
Reply to post by chris reid, on March 16, 2003 at 21:34:16:

The may not be at all unstable. The tree has grown over the wall not for support, but because the wall was in the way. It is quite likely that the tree has sufficient support roots behind the wall and down below into the soil downslope. It may be that growth of the tre is pushing the wall out.

You need to demonstrate that the tree is stable without the wall. This means finding a way to analyze the root pattern behind and below the wall.
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<Stephen Wiley>
Reply to post by Russ Carlson, on March 16, 2003 at 21:34:16:

I think Russ may unintentionally ommitted the word "tree" in his opening sentence.

Chris, my impressions of your site description, led me to the same conclusions as Russ stated. I encourage you although to follow up with your contacting a qualified arborist in your area. As their may be more structural or health issues, or other variables not listed in your post (e.g. root fungus, additional erosion causes such as increase ground water due to offsite disturbances).
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