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Responses of Northern U.S. Forests to Environmental Change
ISBN 0-387-98900-5

Chapter 7: Tree Health and Physiology in a Changing Environment

Walter C. Shortle, Kevin T. Smith, Rakesh Minocha, Subhash Minocha, Philip M. Wargo, and Kristiina Vogt

Tree rings are good measures of growth and indicators of health. Tree ring characteristics are a composite response to intrinsic and extrinsic factors, and although growth is integrative, it is restricted by the essential factor that is most limiting in supply. Trees sampled at or near the edge of their range are likely to contain a stronger common signal, especially of climate. Given these principles, the use of tree rings as a proxy record of climate or environmental disturbance depends on uniformity of linkage between external conditions and tree biology. Separating the signal of external and internal factors in the tree-ring record can be difficult.

Based on a large sample of red spruce tree rings, enrichment of Ca and Mg evident in stemwood formed in the 1960's is consistent with the mobilization of base cations in the soil, which also coincides with increases in the atmospheric deposition of nitrates and sulfates. Root physiology and pathology are affected indirectly by acidic deposition, through changes in soil chemistry and through changes in carbon allocation patterns to the roots. The Ca/Al molar ratio of the soil solution seems to be one of the prime mechanisms by which acidic deposition affects forest growth and is an important indicator of potential stress.

The availability of biological markers that can assess the current status of stress in apparently healthy trees in a forest is crucial for planning a potential treatment or management practice for mediating or removing the stress. In conjunction with soil chemistry, putricine and/or spermidine may potentially be used as early indicators of Al stress before the appearance of visual symptoms in red spruce trees.

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