In many sub-Arctic forest ecosystems, the colonization and growth of white spruce trees are initially made possible by the presence of alder shrubs, which enrich the nutrient-poor soil with nitrogen. As the spruce trees grow taller and develop dense canopies, however, they begin to block essential sunlight from reaching the forest floor, eventually shading out and eliminating the lower-lying alders. Without the alders to continually replenish the soil's nitrogen levels, the nutrient quality of the ground gradually deteriorates over subsequent decades. Consequently, the spruce forest's own long-term growth rate slows down significantly, leaving the weakened trees vulnerable to devastating pest infestations and preventing the forest from achieving a stable, permanent climax state.
The relationship between the white spruce trees and the alder shrubs, as described in the passage, is most analogous to which of the following scenarios?
- AA chemical plant releases warm wastewater into a nearby river, which accelerates the growth of an invasive algae species that eventually blocks sunlight, killing native aquatic plants.
- BA nation's government subsidizes a new solar power industry to reduce reliance on fossil fuels, but the high taxes required for the subsidy eventually bankrupt the solar companies, forcing the government to return to fossil fuels.
- An online retailer relies on a local courier service to build its customer base by offering cheap, rapid deliveries. As the retailer's sales volume surges, its demanding delivery schedules overwhelm the courier, driving it out of business. Lacking the courier's specialized local network, the retailer's delivery times plummet, causing customers to abandon the retailer for competitors.Answer
- DA species of vine uses a sturdy oak tree for physical support to climb toward the forest canopy, gaining access to sunlight without affecting the tree's growth.