Britannica
Sources used in this answer
Why do trees weakened by acid rain become more vulnerable to drought and pests?
Created from Britannica articles
using AI.
AI can make mistakes, so verify using Britannica articles.
Acid rain
Forest dieback caused by acid rain in the Jizera Mountains, Czech Republic.
Trees weakened by acid rain become more vulnerable to drought and pests primarily because the pollution alters soil chemistry and directly damages plant tissues, leaving the trees physiologically stressed.12
The process occurs through several key mechanisms:
- Nutrient Depletion: Acid deposition leaches essential base cations—such as calcium and magnesium—from the soil. These nutrients are vital for proper plant growth and health.12
- Toxic Exposure: As soil acidity increases, it mobilizes aluminum into a toxic, dissolved form. This can damage tree roots and inhibit their ability to take up necessary nutrients and water.12
- Direct Tissue Damage: In some species, such as red spruce, acids leach calcium directly from the cell membranes in their needles. This damage makes the trees significantly more susceptible to freezing and other environmental stressors.1
Once a tree is compromised by these factors, its natural defenses are lowered, making it much harder for the tree to survive secondary threats like drought, insect infestations, and pathogens.12