Geeze, if only I would have really paid attention in those Science classes rather than staring out the window and daydreaming. Perhaps I would know the answer to this question based on a recent observation from the field.
My wife took a series of photos of rocks adjacent to a lake. The images clearly depict a water line of sorts.
So, I researched littoral zones, eulittoral zones, lakes, vegetation, high water, Southern exposures, lichen, types of rocks etc. Why does nothing grow upon the rocks below the high water marks? The water is well below this mark for many warm months during the Summer. The water doesn’t rise up to this level for many months after Summer. Snow/Ice covers much of this area at times. I just wonder the why of it.
My wife took these images not with that question in mind, but rather she intuitively sensed the contrast and starkness of it all in a harsh environment. Perhaps someone with a greater grasp of science or more common sense than I can answer the question?