Final answer:
The The correct answer is option c. The greatest species richness in an ecosystem after clear-cutting is typically observed 5 years later, when intermediate species have begun to establish themselves but before the ecosystem has stabilized into a climax community.
Step-by-step explanation:
At which time after clear-cutting does the ecosystem exhibit the greatest species richness? The answer is c) 5 years later. Initially, after a disturbance such as clear-cutting, the ecosystem experiences a rapid growth of pioneer species. These are often species that are quick to colonize open and disturbed areas, but they don't necessarily contribute to high species richness. As succession progresses, more species, including intermediate species such as grasses, forbs, and small trees, start to establish themselves within the first few years.
Research from the Brazilian Amazon and studies on secondary succession suggest that intermediate stages of recovery host a greater diversity of species. For example, after clear-cutting and the establishment of tree monocultures, biodiversity measured in these areas was greater in 4-5 year old plantations compared to newer ones. Similarly, secondary succession in forest fragments showed significant changes in species composition within a 5-year period.
As more time passes, the ecosystem begins to stabilize and moves toward a climax community. While a 100-year-old forest might have a stable and rich ecosystem, it is during these intermediate years—around 5 years after the disturbance—that species diversity tends to be the highest. Therefore, 5 years later is typically when the greatest species richness is observed after such an event as clear-cutting, preceding the establishment of a more stable but less species-rich climax community.