The Figure Below Illustrates How, Although Pines First Established Themselves

The figure below illustrates how, although pines first established themselves as the dominant tree in the Lake Michigan sand dune community, black oaks ultimately become the dominant species.
What best explains the gradual reduction of the pine?

A) Oaks trap sand, causing the dune to level out; pines can only survive in the low, protected areas between the dunes.
B) Pine needles and the shade from existing pines improve the soil composition and moisture, allowing oaks to become established and preventing new pines from surviving.
C) Pines replace the grasses but this destabilizes the dune and increases the amount of moving sand; the loss of pines is not related to the presence of the oaks.
D) Actually oak seeds were always present in the sand; they simply require more time to germinate.