Question

which statement below best summarizes the likely effects on the carbon cycle of clear - cutting, or removing all of the trees, in vast areas in a forest?

• clear - cutting would reduce the amount of carbon dioxide found in the atmosphere.
• clear - cutting would limit the amount of nitrogen - fixing bacteria in the area.
• clear - cutting would allow for secondary succession of smaller plants and more carbon.
• clear - cutting would increase the amount of carbon dioxide found in the atmosphere.

Explanation:

To determine the correct answer, we analyze each option:

• Option 1: Trees take in \( \text{CO}_2 \) via photosynthesis. Clear - cutting removes trees, so \( \text{CO}_2 \) uptake decreases, and atmospheric \( \text{CO}_2 \) should increase, not decrease. So this option is wrong.
• Option 2: The question is about the carbon cycle, and nitrogen - fixing bacteria are related to the nitrogen cycle, not the carbon cycle. So this option is irrelevant.
• Option 3: Secondary succession of smaller plants would have less biomass than the original forest. Smaller plants take in less \( \text{CO}_2 \) and store less carbon, so there would be less carbon storage, not more. So this option is wrong.
• Option 4: Trees perform photosynthesis to remove \( \text{CO}_2 \) from the atmosphere and store carbon. When trees are clear - cut, photosynthesis stops, and the stored carbon in trees is released (through decomposition or combustion), which increases the amount of \( \text{CO}_2 \) in the atmosphere. This option correctly describes the effect on the carbon cycle.

Answer:

D. Clear - cutting would increase the amount of carbon dioxide found in the atmosphere.