Colorful fall foliage is one of the characteristic signs of autumn throughout much of the eastern United States, and sugar maples, with their brilliant orange and red leaf colors, are one of the signature trees. Acid rain is threatening to reduce the number of sugar maples in our forests, alter the forest ecosystem, impact the maple sugar industry, and reduce the colorful fall brilliance. Although pollution controls since the 1960s have reduced the amount of sulfuric acid in the atmosphere, the amount of nitric acid from automobile pollution has not decreased. This has resulted in highly acidic forest soils.
Researchers at Cornell University investigated the influence of acid soils on sugar maple growth. Because nitric acid and sulfuric acid leach calcium -- an essential plant nutrient -- from the soil, in 1999 the researchers added calcium to a sugar maple test plot at their research facility in North Woodstock, New Hampshire, to replicate the soil conditions that existed 25 years ago, prior to the acid rain era. Every year since then, sugar maple growth in the test plot and in a similar, non-treated plot has been evaluated.
Within a few years the acidity in the top levels of the soil on the calcium-treated plot had neutralized. The sugar maples' response was better seed production, seedling germination, and root growth. Adult sugar maples in the untreated plot continued to decline and produced fewer seedlings.
This research suggests that highly acidic soils resulting from nitric acid pollution are creating a soil environment that's harmful to sugar maple growth and reproduction.
For more information on this research, go to: Cornell University.