[CANUFNET] Tree opening Innovation

[Grady Lazenby]

Wow Jim!
Thanks for your reply, I've read your book! Many good solutions for me to explore I will let you know what I come up with! Please see pic for a representative of my target trees.
Grady Lazenby


From: CANUFNET [mailto:canufnet-bounces at list.web.net] On Behalf Of James Urban
Sent: Tuesday, August 11, 2015 10:53 AM
To: Canadian Urban Forest Network
Subject: Re: [CANUFNET] Tree opening Innovation

Grady:

I think this approach may be ok and an interim step between grates and just a gravel mulch.  Gravel is my personal favorite if you cannot sell mulch or ground cover plantings.  Toronto is using un-stabilized coarse gravel in many tree spaces and this is working just fine.  There are several types of resin bonded rubber products and resin bonded gravel.  My observation is that the bonded gravel is brittle and breaks into chunks while the rubber bonded material is stronger and holds together better and can move a bit as the roots lift the tree.  BUT there is a down side to stronger!  I have seen these girdle the tree in a short amount of time, particularly small trees and trees planted too deep.  This material is going to move as the tree grows like any other surface on top of the root system.  it should only be considered a temporary surface that may have to be removed in 10-20 years.  There are no permanent surfaces that you can put on top  of tree roots in a small space.  They will all move and change over time as the tree matures. That is why just plane gravel is best.   The other problem is that you cannot access the soil to check anything.  So here is my suggestion:

1.  Use the resin bonded rubber product but keep the material at least 12" from the face of the trunk.  You will need that much space to keep the material away from the trunk until the tree is large enough to out compete it on strength.

2.  Feather the thickness of the edge of the material at the edge near the tree to about 1/4 inch so the trunk can slowly tear the material as it lifts and pushes on the material.

3.  Use the same aggregate that is in the matrix (but un bonded) to fill the transition space between the resin bonded material and the tree trunk.  Yes some of the loose material will get displaced over time but is a needed function of growing mature trees.

4.  Do not use the manufactures detail of placing a subbase bedding under the surface.  This extra sub-base is for vehicle loading, which will not happen in the tree space or maybe is suppose to make this surface acceptable for handicapped people but it is not going to stay flat or level forever even with the subbase. Roots and trunk flares can blow away solid concrete so a little resin bonded gravel is not going to stop a mature tree.

5.  Add inspection holes in at least two place in opposite corners outside the rootball.  These can be round 6" diam irrigation valve boxes cut to the correct depth.

Jim Urban, FASLA / Urban Trees + Soils
915 Creek Drive / Annapolis, Maryland 21403
Cell         410 693 9053     Office 410 263 4838
jimtree123 at gmail.com<mailto:jimtree123 at gmail.com>
http://www.jamesurban.net



On Aug 11, 2015, at 12:13 PM, Grady Lazenby <GLazenby at abbotsford.ca<mailto:GLazenby at abbotsford.ca>> wrote:


Hello,
I'm currently looking at replacing some of the metal grates currently being used here in Abbotsford. The solution I like the best is the resin bonded Birdseye gravel setup. Does anyone have any experience with these? I am aware of the possible change to the PH levels of the soil under the material but I'm specifically wondering about the life span of this product and any other associated problems with it. Also, if anyone out there has a new product that they are using and have gotten good results I would be eager to hear about it.
thx

Grady Lazenby
Arborist 2
Parks, Recreation & Culture
Tel: 604-853-5485 ext. 5915
<image001.jpg>


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