Answer: I wonder which had more effect on the increased vigor of your trees; the terracing, or the removal of the Aptenia groundcover? Sloped areas shed water quickly, but flat areas provide a place for water to rest and percolate down into the soil. This increased moisture may have been all that your trees needed for better health. While it's true that groundcovers can compete with tree roots for moisture and nutrients, usually it's the trees that win. Aptenia has a relatively shallow root system, but it can grow thick and dense so perhaps it was deflecting water rather than allowing water to percolate down to the roots of your trees. In any event, I'm happy your trees are doing well. A well-behaved groundcover replacement for the shady areas under your trees could be Bergenia, Cornus canadensis, Galium odoratum or Oxalis oregana.
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