Expert: Jim Hyland - 5/7/2007

Question
QUESTION: I have a 60 foot pine tree in my back yard.  Two large roots on different sides of the tree about 12 inches in the ground are pulling up my block fence.  I am concerned if I cut these roots it will compromise the tree .  The tree would cause major damage in any direction it falls.  Would you suggest removing the tree or cutting the roots.
ANSWER: Pines have a tap root and cutting some of the side roots will not greatly effect stability of the tree. It might however affect the health of the tree. In depends on how close the tree is to the fence and how much of the root system you are going to cut.

You can cut the roots back but I would recommend that they be cut as far away from the trunk of the tree as possible along the fence would be the best. The amount of roots that can be cut is generally a percent of the root area. You can cut up to 20% of the root on a side without causing damage to the tree. Think of the root system area as a pie and as you cut across the pie keep the amount cut off below 20%. I would cut a trench along the fence down to 18-24 inches and install a root barrier along the patio. These barrier will keep the roots as they grow back from going under the fence.
The fall would be a good time to do this since the tree will have less stress all the tree's energy will be in growing roots rather than leaves.
I would dig the trench and cut the roots and see what happens --I would expect a little die back of a few limbs on that side of the tree. IF the tree were to die you can take it down then but I would think all would be ok.


---------- FOLLOW-UP ----------

QUESTION: Thanks for your quick response!  Unfortunately the trunk is within two feet of the block fence on both sides.  My guess is I would have to cut between 50 to 70 % of each of the two roots doing the damage.  It sheds needles like crazy in the summer and clogs up my gutters.  I love the majestic pine, but I am thinking cutting this much of two large roots (about 6 inches wide each)  would really be traumatic for this tree . The yard is small and the proximity of neighbors roofs inclucing mine are close . The possibility of this tree losing stability in a Phoenix summer monsoon storm will keep me up at night.  What do you think?  

Answer
Cutting 50-70%  of the pines roots will more than likely kill the tree. You will have to balance whether the roots damaging the wall is all that bad (this is a slow process and more than likely has been going on for a long time.) with the shade the tree provides with the choice of having the tree taken down (this can be  costly) and/or cut the roots and see what happens--if the tree dies have it cut at that point. Since I can not see the wall and its location and condition it would be hard for me to make this call. I personnel would look hard at the wall and try to keep the shade.