After a forest fire, secondary succession occurs in an ecosystem. which of the following statements best explains why pioneer species are replaced by other "climax" trees?
a. the fast growing trees and other pioneer species absorb environmental pollutants more quickly than the "climax" trees and die off, leaving space available for the "climax" trees.
b. the "climax" trees eventually grow taller than the fast growing trees and other pioneer species and shade out the fast growing trees beneath them.
c. the pioneer species change the chemical composition of the soil in a way that favors the growth of grasses and perennials.
d. the roots of the woody pioneers spread through the soil and inhibit the fast growing trees ability to obtain essential nutrients.