A comparison of the severity of paper birch (Betula papyrifera Marsh.: Betulaceae) stand diebacks on two bedrock formations Acadia National Park, Maine

Omand, Kelly A.
Tom Wessels, MA
Department of Environmental Studies
Forest diebacks have generated increasing concern over the past several decades. Several factors have been proposed as dieback facilitators: air pollution, climate change, introduced pathogens and insects, and non-sustainable harvesting practices. Natural cycles of diebacks have also been proposed. Studies on key economic species suggest that pollution plays an important role in forest decline. The Northeast receives some of the nation's worst pollution due to weather patterns, proximity of urban centers, and the region's mountainous topography. Several studies have noted that underlying geology can have a strong effect on the severity of diebacks. Parent material is a key determinant of the nutrient availability of forest soils, affecting their ability to buffer soils from acid deposition. The goal of this study was to compare the health, mortality, and composition of Aspen-Birch stands growing on various underlying substrates at Acadia National Park, Maine. This site offered a unique opportunity to compare fire-generated stands (dating to 1947) rooted on the adjacent Cadillac Granite (CG) bedrock and the richer Shatter Zone (SZ) formation, which is composed of a heterogeneous mixture of granite and metasedimentary rocks. Superficial deposits ranged from marine sediments to glacial till and undifferentiated bedrock/thin draft. Canopy sampling was used to assess birch size, canopy class, mortality and health. Soil samples from each canopy sampling site were assessed to compare soil elements, pH, and Effective Cation Exchange Capacity (ECEC) among the Aspen-Birch stands occupying the various substrates. Results indicate significantly higher percent birch mortality in CG stands. DBH of CG birches was significantly lower that that of SZ birds. Crown position analysis indicated that a low percentage of birches were being overtopped by later seral species, implying that current birch decline in Acadia is not driven mainly by succession. Soil analyses revealed a pattern of significantly higher nutrient levels and ECEC among SZ sampling sites, as well as on particular surficial deposits, supporting the hypothesis that higher nutrient levels and buffering capacity may mitigate the impacts of stresses initiating paper birch stand decline.

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