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The relationship between long-term foliar decline assessments and annual growth of sugar maple in Ontario, Canada.

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Title: The relationship between long-term foliar decline assessments and annual growth of sugar maple in Ontario, Canada.
Author: Benakoun, Laura
Department: Department of Geography
Program: Geography
Advisor: Gedalof, Ze'ev
Abstract: This thesis presents an investigation of the relationship between visual signs of foliar decline, as represented by a long-term observational index, and annual radial growth of sugar maple (Acer saccharum Marsh.) in unmanaged forests in Ontario, Canada. Dendrochronological records from 24 sites across central and southern Ontario were examined for signs of declining growth, with associated visual decline assessments from 1990-2011 examined for predictive or reactive evidence of observed growth patterns. Foliar decline was found to be moderately predictive of future growth decline, showing correlations 2-3 years in advance of radial growth declines in 46% of plots. In contrast, 25% of sites also showed 2 or more years of correlation between increasing foliar damage and increased growth, although the mechanism responsible for this is unclear. Climate models showed that variation in radial growth was significantly correlated to climate in most study sites. When the effects of climate on growth were removed, the foliar decline / radial growth relationship changed and generally became less predictive. The relationship of growth patterns, foliar condition and site conditions showed no clear pattern across all study sites, suggesting site-specific interactions play an important role in growth dynamics. Overall, sugar maple populations in Ontario show declining growth over the past several decades, although rates of decline vary. The analyses conducted in this study suggest visual assessments of foliar health may be most useful as a predictive management tool once a baseline sensitivity of each plot to foliar condition has been established.
Date: 2016-09
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