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Journal of Environmental Quality Abstract -

Use of Calcium/Aluminum Ratios as Indicators of Stress in Forest Ecosystems


This article in JEQ

  1. Vol. 24 No. 2, p. 209-226
    Received: Apr 1, 1994

    * Corresponding author(s): cronan@maine.maine.edu
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  1. Christopher S. Cronan * and
  2. David F. Grigal
  1. U niv. of Maine, Dep. of Plant Biology, 5722 Deering Hall, Orono, ME 04469-5722;
    U niv. of Minnesota, Dep. of Soil Science, 1991 Upper Buford Circle, St. Paul, MN 55108.



The calcium/aluminum (Ca/Al) molar ratio of the soil solution provides a valuable measurement endpoint or ecological indicator for identification of approximate thresholds beyond which the risk of forest damage from Al stress and nutrient imbalances increases. The Ca/Al ratio can also be used as an indicator to assess forest ecosystem changes over time in response to acidic deposition, forest harvesting, or other processes contributing to acid soil infertility. Based on a critical review of literature on Al stress, we estimate that there is a 50:50 risk of adverse impacts on tree growth or nutrition when the soil solution Ca/Al ratio is as low as 1.0, a 75% risk when the soil solution ratio is as low as 0.5, and nearly a 100% risk when the soil solution Ca/Al molar ratio is as low as 0.2. The Ca/Al ratio of the soil solution can be corroborated with other complementary indices. Our analysis found that threshold conditions for potential forest impacts from Al stress are indicated by four successive measurement endpoints: (i) soil base saturation less than 15% of effective CEC; (ii) soil solution Ca/Al molar ratio ≤1.0 (for 50% risk); (iii) fine root tissue Ca/Al molar ratio ≤0.2 (for 50% risk); and (iv) a foliar tissue Ca/Al molar ratio ≤12.5 (for 50% risk). With appropriate precautions and caveats, these sequential indices based on the Ca/Al ratio provide a means of distinguishing site conditions where Al stress is likely to affect tree growth adversely.

Research supported by the National Council of the Paper Industry for Air and Stream Improvement (NCASI), The Maine Agric. and Forest Exp. Stn., and the Minnesota Agric. Exp. Stn. (Project 25-54).
This is contribution no. 1876 from the Maine Exp. Stn. and contribution no. 2200 from the Minnesota Exp. Stn.

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