How does acid deposition weaken trees?

Acid deposition weakens trees through a combination of direct and indirect environmental stressors that compromise their health and resilience.1

Indirect Effects on Soil

Acid deposition alters soil chemistry by depleting essential base cations—such as calcium, magnesium, and potassium—that are necessary for plant growth and acid neutralization. As these nutrients are leached from the soil, the environment becomes increasingly acidic. Furthermore, this acidification mobilizes toxic aluminum in the soil, which can damage tree roots and inhibit their ability to absorb vital nutrients.12

Direct Effects on Foliage

Acidic precipitation can directly harm trees by leaching calcium from the cell membranes in their needles or leaves. For species like the red spruce, this process makes the foliage significantly more susceptible to freezing damage during winter.1

Once weakened by these chemical changes, trees become less capable of surviving additional environmental stressors, including drought, insect infestations, and pathogen infections, ultimately leading to forest dieback and increased mortality.1