Dr. Randal Johnson
Scholarship of Discovery
Disturbance regimes, which are critical components of forest ecosystems, influence forest morphology, biodiversity, and regeneration. The heterogeneity of disturbance regimes are not well understood on small scales. In this study I analyzed tree cores from five sites within a Tsuga canadensis (Eastern hemlock) forest in northern Wisconsin to investigate disturbance regimes through mean growth release criteria. This study investigated the following questions: 1) Are disturbance regimes in T. canadensis stand level or site specific? 2) If disturbances are site specific, is site location an indicator of disturbance regime? 3) Do site characteristics such as density and tree diameter at breast height (DBH) influence disturbance regime? I found that T. canadensis disturbance regimes are site specific and depend greatly on forest geomorphology, and that density and tree diameter may be weak predictors of disturbance regime. Moreover, I observed a correlation between high intensity release, defined as large increases in ring growth, and low disturbance size, defined as a low proportion of trees with release record, suggesting that T. canadensis may have a differential evolutionary response to gap disturbances dependent on gap size. Though confined to one geographic location, this evidence suggests that T. canadensis disturbance regimes are complex, site specific, and predict growth strategies which ultimately influence forest morphology. The site specificity of T. canadensis disturbance regimes suggest that ecological and management studies, which often assume disturbance homogony, may miss important site differences.
Doolittle, Cole J., "Stand location variance as an indicator of disturbance regime in a monotypic Tsuga canadensis forest" (2019). Honors Program Projects. 103.
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