Date of Award


Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)


Forest Resources


G. Bruce Wiersma

Second Committee Member

Michael E. Day

Third Committee Member

Ivan J. Fernandez


The Bear Brook Watershed in Maine is a paired watershed system; one watershed has been acidified bimonthly with granular ammonium sulfate ((NH4)2SO4) since 1989. The adjacent watershed is used as a reference. This acid deposition treatment presents unique opportunities to look at the long term affects of acidification on vegetation. Acidic deposition continues to be a concern for the health of sugar maple (Acer saccharum Marsh.) in northern hardwood forests. Many studies show a connection between base cation depletion induced by acid deposition and sugar maple decline. In this text we review sugar maple ecology and their response to forest acidification, we investigate the response of sugar maple saplings to chronic N and S deposition, and we compare foliar nutrients of three size classes of sugar maple at BBWM. At the Bear Brook Watershed in Maine (BBWM), we examined the effects of artificially elevated nitrogen and sulfur deposition on sugar maple sapling foliar chemistry, growth, and photosynthetic capacity. We observed a 56% increase in Al and a 25% reduction in mean foliar Ca for sugar maple sapling foliage on the treated watershed compared to reference. Foliar N (+15%), P (+10%), and K (+15%) were significantly elevated in treated saplings. Saplings on the treated watershed had significantly lower carboxylation capacity (-24%), electron transport (-15%), and tri-phosphate utilization (-11%). Net photosynthesis (Anet) was not significantly different between watersheds, respiration was significantly lower in treated saplings, and growth trends and sapling distribution do not show any clear treatment effects. We conclude that saplings, though they show depressed levels of base cations and lower photosynthetic capacity, show little sign of physical decline after 17 years of elevated nitrogen and sulfur deposition. We also investigate the variation of foliar chemistry in sugar maple of three size classes at BBWM - seedlings, saplings, and mature trees. Results showed, independent of deposition levels, mature tree foliar chemistry was at consistently lower nutrient levels relative to juvenile trees, with the exception of higher foliar carbon. Levels of base cations have been declining in mature trees since 1998, along with declines in growth. Seedlings and saplings had comparable levels of most foliar elements, with the exception that seedlings have significantly higher calcium, aluminum, and zinc compared to saplings. Treated seedlings and saplings had significantly lower levels of foliar calcium and higher levels of nitrogen, phosphorus, and potassium compared to untreated juveniles. Differences between mature trees and juveniles were attributed to declines in mature trees across both watersheds, as well as contrasts in rooting, morphology, and stress exposure across size classes. A significant ice storm in 1998 may be responsible for changes in foliar chemistry and growth.