What is the long term effect of the increased primary productivity of a terrestrial ecosystem

The primary productivity can be illustrated as the rate at which the energy gets converted into useful organic compounds by photosynthetic and chemosynthetic organisms. If there is an increase in the primary productivity in an ecosystem, the net primary productivity will also enhance as net primary productivity signifies towards the energy accessible to the primary consumers, which will further results in the availability of enough amount of food.

the answer is c) an oak tree