Why does the author discuss "pyric climax" in the passage? A. To help explain the idea that a forest may not necessarily reach the old growth stage. B. To suggest that fire is a natural disturbance least likely to prevent an ecosystem from reaching its potential climax stage. C. To acknowledge that the pattern of succession following a disturbance is a very different in ecosystems such as grasslands than it is in forests. D. To help explain how the boundary areas of an ecosystem affect the way its structure changes during succession.