Full size Maples are wonderful street trees (ie, planted between curb and sidewalk) except for the commonly seen lifting of sections of sidewalk. Are there useful recommendations to prevent such side walk lifting as the tree matures?
Around here, Acer pseudoplatanus is commonly grown as a street tree like this. All that is done is to take up and re-lay the paving slabs on a new layer of sand every 20 to 30 years or so.
Hmmmm, around here when the roots lift and crack the sidewalk, local codes require the property owner to do repairs. So a contractor gets hired. The contractor breaks up the old sidewalk and hauls it away. Then he cuts the roots off and prepares forms for the new sidewalk to go in at the same level as the original sidewalk. It is a fairly expensive proposition. So . . . that is why I was wondering whether some early preventive actions are effective in protecting the sidewalks without unduly stressing the tree. Though it seems that whacking the offending roots off during the sidewalk "rebuild" doesn't severely damage most of the trees which get that treatment . . . it doesn't have a good feel about it. Would removing/cutting "surface" roots early in the life of the tree, as soon as they become evident, be effective?
Strange! Here, the pavements are local authority property, so repairs are local authority responsibility. Cutting off those surface roots can seriously damage the tree, and may make it dangerous (liable to fall down).
Part of the NAB Maple Society meeting in Atlanta 2007 was a discussion and tour of street trees being tested by the University of Georgia in Athens. There were one or two maples that they were evaluating but I do not recall the species. Below are some pictures from the meeting. I am sure someone will be able to identify the maple. Ed
The source of the problem is the tiny planting spaces. They don't provide enough soil volume for the root systems of a mature tree. Ideally, you would expand the tree well to give a much wider area without pavement or cement. In the example photos, that is not an option. Underground soil vaults beneath the sidewalk would create the tree expanded soil volume. Root barriers are used to try and send tree roots down instead of out, but the roots may grow under the barrier and return to the surface to damage the sidewalk. Another option is to "bridge" the sidewalk over the tree's roots by raising the grade of the sidewalk with a soil base underneath the gravel and cement. This soil allows room for root expansion. It will only reduce the problem, not fix it. Techniques of sidewalk installation may help the problem as well. Placing numerous expansion joints ( as there are in your photos) will allow the sidewalk plates to shift a little before breaking, and once it breaks, repair is easier. Also, look into "rubber" sidewalks that allow some flexibility so the sidewalk bends instead of cracking. Some trees are notorious for damaging sidewalks. Sweetgums, poplars, cottonwoods, maples (red, silver, sugar, norway), birches, tulip poplars, elms have especially shallow root systems are often cited in studies. Also any tree that forms buttressing roots will be much more likely to cause damage to surrounding infrastructure. Sycamores are shown in your photos (2 of them if not all three) and they also are known to cause damage to sidewalks and other infrastructure simply because they grow so large and are often times planted in tiny planter areas. Cutting roots from a tree is never a good idea, and as the roots get bigger, the damage becomes greater. Roots over 1.5-2 inches diameter should only be cut after consulting with an arborist, and when they are cut, proper technique is critical. Large roots (over 6 inches) should be cut with specialized equipment, using either a radial saw, or with huge roots, a stump grinder (with an arborist directing the operation). If root pruning is required, understand that the large wounds are likely to allow fungus, bacteria, and other creatures to colonize the wood, causing decay, that will commonly spread throughout the lower trunk of a tree, creating a hazardous situation that will require removal of the tree sometime down the road. The key take home message is to plant trees in good soils that have adequate volume for them and avoid all these problems.
In my photos, the trees are growing in natural soil, just with the paving slabs laid on top (with a shallow sand foundation immediately under the slabs). The trees are at least 60-70 years old, and mostly in reasonably good health. The idea of separate 'underground soil vaults' hadn't been thought of back then!
If the homeowner is responsible for PUBLIC sidewalk maintenance and for the management of PUBLICly-owned trees on CITY property, then something is wrong with the municipal structure in terms of the responsibility/accountability framework. Or is this private property that happens to extend to the roadside?
