Which of the following is an effect of acid rain on forest ecosystems?

The correct response highlights the impact of acid rain through the acidification of soil nutrients. Acid rain occurs when sulfuric and nitric acids are formed in the atmosphere from pollutants and subsequently fall to the ground in precipitation. When this acidic rain infiltrates the soil, it can lead to a decrease in pH levels.

As the soil becomes more acidic, essential nutrients such as calcium and magnesium can leach away, making them less available to plants. This deficiency can hinder plant growth and disrupt the balance of the forest ecosystem, as many trees and plants rely on these nutrients for proper physiological functions. Additionally, the shift in soil chemistry can also negatively affect soil-dwelling organisms, further impacting the health of the entire ecosystem.

The other options suggest outcomes like promotion of new species growth and increase in plant growth, which are unlikely in the presence of acid rain as the acidic conditions are more harmful than beneficial. Reduction of carbon dioxide levels does not directly correlate with the effects of acid rain on forests either; rather, it’s the soil's nutrient balance and overall health that suffer from acidification.