You are a young scientist who is not yet able to identify specific plant species. You walk through a forest and note that there seem to be four kinds of trees: A, B, C, and D. You can tell there are four different species even if you do not know exactly what they are. The specimens of $A$ and $B$ seem to be all quite old, though still healthy. Of the specimens of $C$ and $D$, some are mature, but not old, while others are at various levels of maturity. Among the plants making up the understorey are seedlings and saplings of C and D. No seedlings or suplings of species $A$ and $B$ are found.
(a) In terms of the process of succession, describe what stage this forest has reached. Explain.
(b) Describe specifically what this area will look like after 150 years.
(c) Explain why it will look different than it does now.