Here is a paragraph from a passage talking about feeding habits of east african herbivores:
When biologist Richard Bell and his colleagues analyzed the stomach contents of four of the five species (they did not study buffalo), they found that each species was living on a different part of the  vegetation. The different vegetational parts differ in their food  qualities:  lower down, there are succulent, nutritious leaves;  higher up are the harder stems. There are also sparsely distributed, highly nutritious fruits, and Bell found that only the Thomson’s gazelles eat much of these.
What are the contextual meanings of the words/phrases that are in bold? I think that vegetation means "plant". But I didn't understand the others.