Peter Palmiotto, PhD
Department of Environmental Studies
This study examined relationships among foliar chemistry, photosynthetic function and crown health in sugar maple and yellow birch tress in the White Mountain National Forest of New Hampshire and Maine, USA. The purpose of the study was threefold; (1) to investigate whether Mn might negatively impact sugar maple nutrition and health, (2) to supplement visual measures of health with a more quantitative approach, and (3) to determine whether Mn stress might impact sugar maple and yellow birch in the same ways. Since Mn concentrations are difficult to quantify in soil, foliar chemistry was used as a surrogate for soil chemistry. Chlorophyll fluorescene – a technology that assesses the efficiency of photosystem II – was used as a proxy for overall photosynthetic functioning. Standard Forest Inventory Analysis and North American Maple Project protocols were followed to visually assess tree health. Results showed no discernible difference between visual crown assessments and chlorophyll fluorescence measurements; neither method proved to be more robust than the other in detecting symptoms of decline. There were, however, significant, negative correlations between foliar Mn and foliar Mg in both sugar maple and yellow birch, and between foliar Mn and foliar Ca in yellow birch only. Mn was not correlated with visual assessments of crown health unless it was paired with Ca of Mg. Mn:Mg and Mn:Ca molar ratios showed significant, negative correlations to crown health with sugar maple only. Foliar Mn did not show any significant relationships with chlorophyll fluorescence, though foliar N was strongly correlated with photosynthetic functioning in both species. Comparing foliar Ca and Mg to chlorophyll fluorescence parameters produced surprising, negative correlations. In addition, sugar maple Ca values, and Mg concentrations for both sugar maple and yellow birch were significantly, negatively correlated with N. On the whole, the different trends sugar maple and yellow birch showed vis-à-vis foliar chemistry, health, and photosynthetic functioning intimate that these two species respond differently to nutrient availability and nutrient stress. The absence of data showing a correlation between Mn and tree health suggests that this element might not yet play a significant role in sugar maple decline, except insofar as it interacts with other nutrients. Future investigations are needed to further elucidate the relationship among increased foliar Mn and N, decreased foliar Ca and Mg, and tree health.