Abstract
Vegetation was measured in seven stands on similar sites in a 50-km portion of the upper Ohio River Valley. These stands lay along gradients of chronic exposure to airborne chloride (Cl), sulfur dioxide (SO2), fluorides (F), and possibly other pollutants. Species richness, evenness, and Shannon diversity index were generally depressed within the overstory, subcanopy, and herb strata near industrial sources of air pollutants. A significant relationship between coefficient of community and combined air pollutant index (relative exposure of stands to Cl, F, and SO2) showed that similarity in species composition decreased along a gradient of increasing air pollutant exposure. Increasing air pollutant exposure reduced overstory stem density, but abundance of vegetation in other strata tended to increase along the same gradient. The relative importance of Acersaccharum Marsh. was greatly reduced in all strata with increasing pollutant exposure, whereas Aesculusoctandra Marsh. appeared tolerant of air pollutant stress. In understory strata, the importance of Linderabenzoin (L.) Blume increased with increasing pollutant exposure.

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