The Effects of Experimental Acidification on Understory Plant Communities at the Bear Brook Watershed in Maine

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Kenlan, Peter H.
Effect of Chemicals on Plant communities; Experimental Acidification; Bear Brook Watershed; Environmental Sciences; Forest Sciences; Soil Science
thesis / dissertation description
Acidic deposition in the form of elevated nitrogen (N) and sulfur (S) loading is of continuing concern in the Northeast United States where such deposition is known to cause depletion of soil base cations and increased mobilization of aluminum (Al). The Bear Brook Watershed in Maine (BBWM) is an experimental study site designed to study the changes to soil, water and vegetation caused by acidic deposition. BBWM is a paired watershed site with one reference watershed and one watershed that has been treated with granular (NH4)2S04 bimonthly by helicopter at a rate of 28.8 kg S ha -¹ yr -¹ and 25.2 kg N ha -¹yr -¹ since 1989. A series of 101 plots were established to characterize understory plants species at BBWM with regard to species composition, diversity, abundance, frequency of occurrence and biomass. Tissue samples were collected from Acer saccharum seedlings and from Uvularia sessilifolia to determine whether there were differences in the chemical composition of these plant tissues. The treated watershed exhibited a generally lower abundance and frequency of understory plants and significantly less Acer pensylvanicum and Aster spp. Measures of community similarity and diversity indicated a very high degree of similarity and equal diversity. Analysis of tissue chemistry from the two species collected showed higher N concentrations and lower base cation concentrations in the treated watershed except for potassium (K) in Acer saccharum. Results from this study show that there are important differences between the understory plant communities in the two watersheds and suggest that the enhanced deposition may play a role in causing these differences. However, without data from a longitudinal study of these plant communities, the degree to which enhanced deposition may be responsible remains unclear.