Century old trees and evolution

Question

We always think of natural selection as occurring at the level of populations not individuals. how about century old trees where germline is being produced from constantly dividing cells. Are all meristems in an old tree sharing the same genetic material, or enough mutations occur that different meristems have a different genetic background and are being selected differentially? Do different cells in a tree behave evolutionary more like different populations?

Added Note: The point I was trying to make is that for multicellular organisms in which the germline/somatic separation does not occur early in life, maybe Lamarck was not that wrong. In school we always learn to ridicule Lamarck with the giraffe story. But maybe in some instances Lamarckism makes at least as much sense as Darwinism.

Answer 1

Yes, indeed, somatic mutations can and do occur on different branches of a plant. Here is a recent study exploring this concept in an annual herb (rather than an old tree), and showing that selection is active in filtering these mutations during growth of the plant. From the end of the abstract:

These results support the hypothesis that somatic mutations accumulate during vegetative growth, but they are filtered by different forms of selection that occur throughout development, resulting in the culling of expressed deleterious mutations and the retention of beneficial mutations.