As early as the 1960s, scientists observed evidence of tree damage from acid rain and other environmental pollutants in the Black Forest of Germany. First termed Waldsterben, or tree death, this phenomenon caused damage to nearly half of all trees in the Black Forest by 1990. Acid rain harms wildlife, and while most acid rain studies focus on aquatic animals, the forests are not immune to the effects of acid rain.
During rainfall, some water soaks into the forest soil; when the rainfall itself is acidic, it can cause the acidity of the soil to increase. Some soils include a natural buffering capacity, which means the soil neutralizes the acidity in the soil. These soils are naturally alkaline, but the buffering abilities can be damaged through frequent acid deposition. Those soils that have less buffering capacity are more susceptible to the other harmful effects of acid rain. Farmers might add crushed limestone, which is an alkaline material, to help increase the soil’s buffering capacity.
In addition to increasing the acidity in soil, acid rain leaches cations like potassium, calcium, magnesium and sodium from the soil and washes them away, making these nutrients unavailable to plants. Known as soil depletion, this process reduces the fertility of the soil. When acid rain removes those nutrients completely, the soil is unable to support plant life. Acid rain also releases substances like aluminum, which are toxic to plants.
Forests at high elevations, such as those in the Great Smoky Mountains, are greatly affected not only by acid rain but also because of exposure to acidic clouds and fog. With frequent exposure to acidic fog, the waxy coating of leaves and needles of trees may weaken and be more prone to damage from insects, disease or cold weather.
When plant life cannot be supported, animal life suffers as well because of the loss of habitat or food sources. Biodiversity might decrease, meaning the number of distinct environments as well as the number of species that reside in those environments could be lost. Species within a given habitat rely on each other. For example, low levels of calcium in soil caused by acid rain might decrease the number of earthworms or other insects that birds need for nourishment; additionally, when snails are not present, female birds do not get enough calcium for healthy eggs. As a result, the populations of these birds also decrease.