Effects of chronic ammonium sulfate treatments on forest trees at the Bear Brook Watershed in Maine

• Main Author: White, Gregory J
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-1996
• Subjects: Botany; Ecology; Forestry; Plant sciences
• ISBN: 0591228343; 9780591228342

The responses of forest trees to chronic $\rm(NH\sb4)\sb2SO\sb4$ additions were examined at the Bear Brook Watershed in Maine, a paired watershed study designed to assess responses to chronic additions of acidifying substances. Responses evaluated included (1) foliar chemistry of hardwoods and red spruce; (2) nutrient resorption dynamics of hardwoods; (3) wood production and relative density in red spruce; and (4) the development of frost hardiness in red spruce. Significant differences were observed in foliar chemistry between the watersheds for N, P, Ca, K, and Al. Increased N on the treated watershed is likely due directly to the $\rm (NH \sb4)\sb2SO\sb4$ treatments. Other differences observed are probably due to indirect changes in soil chemistry caused by the $\rm(NH\sb4)\sb2SO\sb4$ treatments. These trends in foliar chemistry corroborate earlier water chemistry studies at this site. Differences were observed between the watersheds in terms of nutrient resorption proficiency, as measured by terminal content in senesced leaves. However, resorption efficiency (fraction of the nutrient content of the green foliage retained by the plant) showed no significant differences between watersheds except for American beech. No differences in red spruce radial growth or relative density of wood produced were observed between the two watersheds. Possible explanations for this include: (1) differences in foliar N pre-dated the treatment; (2) another resource not affected (or negatively affected) by the treatment limits growth; (3) growth response to increased N has manifest itself in ways other than radial growth or wood density; and (4) increased radial growth and/or density of wood produced has not yet occurred, but may at a later date. Mean freezing injury for red spruce foliage increased with decreasing test temperature for both watersheds, and was significant for the three lowest test temperatures tested. Damage was not statistically different between watersheds except at 45$\sp\circ$C, where the mean injury index was greater on the untreated watershed. This indicates that although there was no apparent difference between watersheds in terms of the temperature at which damage occurs, the relative amount of damage occurring at $-$45$\sp\circ$C is greater in mature red spruce from the untreated watershed. Damage index at this temperature was found to be significantly correlated with foliar N concentration.