Which of the following best explains the natural cause of a decrease in biomass as succession peaks in a climax community? Select one:
a. Once a climax community is reached, there are no nutrients left in the ecosystem to support the growth of plants.
b. The canopy of forests prevents sufficient light from reaching the forest floor, thereby limiting primary productivity.
c. Humans usually cut down old growth forests.
d. The presence of large animals such as elk or wolves prevents the development of young animals.