Final answer:
The most immediate effect of removing many trees from a forest by logging is increased rates of decomposition, which leads to higher atmospheric CO2 levels and contributes to global climate change. So the correct option is A.
Step-by-step explanation:
If many trees are removed from a forest by logging, the most immediate effect on the carbon cycle in that forest is increased rates of decomposition. Trees play a critical role in the carbon cycle by capturing carbon dioxide (CO2) from the atmosphere during the process of photosynthesis and storing carbon in their biomass. When trees are removed, there is less photosynthesis occurring, which means less CO2 is being removed from the atmosphere and sequestered. Additionally, the felled trees, unless utilized or managed, will start to decompose, releasing stored carbon back into the atmosphere as CO2. This contributes to higher atmospheric CO2 levels and can enhance the greenhouse effect, leading to global climate change.
The immediate impact is not a decrease in atmospheric CO2, decrease in fossil fuel combustion, or increased production of organic compounds, but rather the opposite when considering the reduction in live biomass. Deforestation contributes significantly to rising CO2 levels, which in turn affects global climate patterns and can result in habitat loss, biodiversity loss, and adverse environmental consequences.