Oak Mortality Patterns in the Midwest U.S.A.

Rose-Marie Muzika and Randall Morin

Published May 2019 in International Oaks No. 30: 341–348

Abstract

Episodes of oak mortality, primarily associated with oak decline have been documented for at least 40 years in the lower Midwestern United States, particularly the Ozark Mountains physiographic region. In many ways, oak decline and mortality define the mid to late successional Quercus resource in that region and have contributed to successional development patterns. Trends associated with the latter half of the 20th century include dieback, decline, and mortality of Quercus, section Lobatae (Red Oaks). More recently, however, section Quercus (White Oaks) species have experienced mortality in a rapid manner. Etiology of decline and mortality between the two oak sections differs notably. We use a quantitative spatial and temporal analysis of repeated measurement plots to examine patterns in mortality across the region. Periods of Red Oak decline and mortality have been associated with discrete events such as drought years, but site conditions, stand density, and forest age contribute to the observed decline and mortality events. Recent concern and investigation into White Oak mortality reveals an absence of decline, per se, but abrupt mortality on otherwise vigorous individuals and forests. Phytophthora represents the most consistent biotic agent associated with White Oak mortality. This quantitative spatial and temporal indicates the importance of examining region- and subregion- wide mortality in addition to within forest patterns in order to develop hypotheses about current and future mortality and to understand forest change in a broad ecological context.

Keywords

oak decline, Quercus section Quercus, Quercus section Lobatae, forest inventory

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