What does it mean that the forest has surface trees, a shallow surface-dweller layer, and deeper decay and bedrock layers? Is there something meaningful (in te

What does it mean that the forest has surface trees, a shallow surface-dweller layer, and deeper decay and bedrock layers? Is there something meaningful (in terms of linear continuity) on the y-axis of a forest? Or are you looking for a continuous function to apply where the metaphor isn't asking for one?