We discovered the tenacious evergreen sprig on our daily walk. Grandfather pitied the seedling clinging to bare stone. A full-grown pine needed access to the earth’s nutrients, and the minuscule reserves in the stone’s clefts and crevices would stunt the tree if it lived at all.

I was only a child, but I vowed to help the sapling. On warm days, we carried water. We sheltered it from storms and patted dirt at its roots.

Today my grandson and I took a walk. I introduced him to the ...