Question
QUESTION: I have a ring of dead grass around each of my Live Oak trees.  The trees are no more that 5 years old.  Almost everyone on the street and in the neighborhood has the same problem with the same type of tree.  It is a young subdivision and was farm land prior to the subdivision being built.  The rings are no where else in the lawn, just around the trees on the outer edges of the branches.

ANSWER:  I take it that there is a band of dead grass around each tree roughly corresponding to the drip line of the tree. Has this now shown up or has it been in place all these five years? I am thinking that it is related to the material that was used to stabilize the root ball when the trees were planted. Surely there must be some resident who will remember what was done at the time. The long term health of the trees may have been compromised.

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

QUESTION: When we bought the house approx. 3 years ago the amount of dead grass was smaller.  The trees themselves do not not look unhealthy.  In fact they seem to be doing quite well.  The trees in my neighbors yards seem to be doing fine as well.

You are correct in the assumption it is at the drip line of the tree. However after double checking there is an additional dead ring of grass approx. 6 feet past the drip line  Everyone in the neighborhood seems to think it is the root system drawing nutrients from the soil.  Could this be the problem?  If it is what you say it is can anything be done to correct the problem?  The tree is too big to dig up, the trunks are about 6-8" in diameter.  

Thanks,

Dennis

Answer
So the band of dead grass is growing outward. Is it in fact so or it only appears so because there is little or no grass inside the dripline?
Before the trees were installed, a hole was dug to accommodate them. The excavated soil was used to back fill the the installation so that the trees would be stable. Sometimes fertilizer and soil amendments are incorporated. What if a contaminant got in there? A weedkiller for instance. This contaminant will leach downward and outward. The "grass" is a collection of small individual plants. Each will react quicker than say, a tree. This contaminant would be diluted in the sap of a tree to the extent that its effects may never be seen, or at least, not in the short term.
If the root system of the tree were to draw all the nutrients from the soil, the grass will show signs of severe nutrient deficiency- not death. I have seen grass growing in arid inert sand; it looked terribly off color and stunted but it was not dead.
Have the trees been mulched at all? At the same time? With the same material? I am thinking that the mulch may contain the contaminant.
All of this is conjecture on my part but it is a challenge to scientifically explain the symptoms in a different way. Until I learn more, "that's my story and I'm sticking to it".