- White, Gregory J.
The Graduate School, University of Maine
The responses of forest trees to chronic (NH4)2SO4 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 (NH4)2SO4 treatments. Other differences observed are probably due to indirect changes in soil chemistry caused by the (NH4)2SO4 treatments. Theses 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 nay 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.
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 watershed except at -45ºC, where the mean injury index was greater not he 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 -45ºC is greater in mature red spruce from the untreated watershed. Damage index at this temperature was found to be significantly correlate with foliar N concentration.