Oak Tree Root Prune Question

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parkerea

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We are putting in pavers near an oak tree, and I am wondering about pruning the roots. I hope someone can help.

Here is the situation:
  • Replacing a very old asphalt driveway with pavers. Selected pavers because they can be removed & replaced if the tree roots lift them, unlike concrete.
  • I don't know the oak variety; see pic of the leaves & trunk.
  • Tree is probably 50 to 60 years old.
  • Trunk diameter 27".
  • Height 27'.
  • Canopy width 28'.
  • Location So California, Los Angeles area.
  • Want to trench about 2' deep along the edge of the driveway to cut back roots, then put down a membrane to reduce root encroachment.
  • Distance from tree to driveway -- 8' to centerline of tree trunk, so the canopy extends about 6' beyond where we would trench.

When the asphalt was removed, we did not see nearly as much roots as I expected, but we have not trenched yet. Internet searches suggest that pruning oak roots can be detrimental to the tree, but the ash trees along our street have had massive root prunes just a couple feet from the trunk several times with no apparent ill effects. (The ash trees lift the curbs and street, so the city does root prunes when the lifting gets excessive.)

Bottom line -- how much impact do you think pruning roots 8' from this oak trunk would have? Any other thoughts?

Thank you.

Oak Tree 2022-10-15B.jpg
 
Possible Holm oak, trenching 8ft from the center of a 27" is going to be very harmful to the trees health. Did the oak ruin the old asphalt drive with surfacing roots?
 
We are putting in pavers near an oak tree, and I am wondering about pruning the roots. I hope someone can help.

Here is the situation:
  • Replacing a very old asphalt driveway with pavers. Selected pavers because they can be removed & replaced if the tree roots lift them, unlike concrete.
  • I don't know the oak variety; see pic of the leaves & trunk.
  • Tree is probably 50 to 60 years old.
  • Trunk diameter 27".
  • Height 27'.
  • Canopy width 28'.
  • Location So California, Los Angeles area.
  • Want to trench about 2' deep along the edge of the driveway to cut back roots, then put down a membrane to reduce root encroachment.
  • Distance from tree to driveway -- 8' to centerline of tree trunk, so the canopy extends about 6' beyond where we would trench.

When the asphalt was removed, we did not see nearly as much roots as I expected, but we have not trenched yet. Internet searches suggest that pruning oak roots can be detrimental to the tree, but the ash trees along our street have had massive root prunes just a couple feet from the trunk several times with no apparent ill effects. (The ash trees lift the curbs and street, so the city does root prunes when the lifting gets excessive.)

Bottom line -- how much impact do you think pruning roots 8' from this oak trunk would have? Any other thoughts?

Thank you.

View attachment 1024395
Might kill limbs on that side of the tree and might destabilize the tree?
 
Rule of thumb...

Measure the circumference of the trunk (at chest height). Then measure that distance from the edge of the trunk. That is called the "zone of rapid taper" - where the roots go from large diameter to pretty small. Those are the anchors of the tree. Cutting them may not have significant / immediate results on the "health" of the tree, but it can destabalize the tree making it more likely to fail in heavy winds. Over time, the tree will re-anchor...but the question is will it fall down or re-anchor first.

One potential mitigating factor here, the tree didn't put down great roots under the driveway - because roots don't like to grow under impermeable surface. Are you saying you'd put the trench at the edge of the current (but torn up) driveway? That is certainly less concerning than moving that trench closer to the trunk.

It is worth noting that a good base and proper concrete thickness will result in FAR fewer tree/pavement conflicts. When sidewalks are heaved, it is pretty common to see a thin not well compacted base and 3" of concrete. 3" of compact base and 4" of concrete won't see much movement. In fact, there are studies that found sidewalk movement with or without trees...pointing to poor construction as the true culprit. https://urbanforestrysouth.org/resources/nucfac/trees-and-sidewalks-who-exploits-who
 
Thank you all for your input. After digging the trench, we decided to leave the large roots intact. There were some much smaller roots near the surface, and several large roots over a foot down. We will leave the large roots, and will pour concrete above them to hopefully inhibit the surface roots from invading the pavers.

Thanks again, and take care.
 

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