In the graph we see the population of primary and secondary consumers, this means, herbivores and carnivores.
We can see that their population decreases within the first year after the fire, which we can attribute to the lack of food for primary consumers, which causes a population reduction on them and, consequently, on secondary consumers.
The population grows again after year one, which means the producers population showed growing too.
From the options, this means that there was an increased transfer of energy from producers to consumers (D)