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Individual Highlight

New Research Suggests Clean Air Act Amendments of 1990 Have Reduced the Exposure of Tree Roots and Surface Water to Harmful Aluminum

Decayed red spruce (Picea rubens) penetrated by fine roots, mycelium, and mycelial cords after 12 years in ground contact. Cords are pathways for wood decay fungus to exchange chemical elements between decaying wood and forest soil. Kevin Smith, Forest ServiceSnapshot : Wood decay fungi add humus to the forest floor with a high proportion of essential calcium and low amounts of potentially toxic aluminum, which are conditions found in favorable growing sites not affected by acid rain

Principal Investigators(s) :
Smith, Kevin T. 
Research Station : Northern Research Station (NRS)
Year : 2012
Highlight ID : 39


National regulation and forest biology have reduced some of the threats posed by acid rain. Recent research by Forest Service scientists suggests that the reduced deposition of sulfates with the Clean Air Act Amendments of 1990 have reduced the mobilization and exposure of tree roots and surface water to harmful aluminum.

This reduction is important because aluminum can be directly toxic to fish and other aquatic life and can be indirectly toxic to trees and other plants. Under acidic conditions, aluminum blocks the use of calcium by tree roots and tends to displace essential calcium stored in soil organic matter.

Additional research points to the fundamental role of forest fungi and the wood decay process that contributes organic matter that is high in calcium and low in aluminum. The common bricktop wood decay fungus was found to occur in decaying logs, the forest floor, and underlying mineral soil, beyond the reach of most tree roots.

This finding suggests that wood decay fungi could use the energy stored in decaying wood to translocate essential chemical elements from deep down in the vertical soil profile up into the tree rooting zone. This process is a potential biological mechanism that restores a healthy chemical environment for forest growth.

Forest Service Partners

External Partners

  • U.S. Geological Survey
  • University of Maine
  • University of New Hampshire