Oak decline in the Ozark Highlands

Background/Question/Methods

Oak decline has impacted Midwestern-upland oak-hickory forests, particularly species in the red oak group (Quercus Section Lobatae) across the Ozark Highlands of Missouri, Arkansas and Oklahoma. Drought is a common inciting factor in oak decline, while advanced tree age is considered a predisposing factor, and opportunistic organisms such as armillaria root fungi and opportunistic insects are believed to contribute to oak decline. Declining trees are initially indicated by foliage wilt and browning followed by progressive branch dieback. If crown dieback continues trees can die. The objective of this study was to analyze oak mortality by species group and inventory year to illustrate the general spatial and temporal trends of oak decline and mortality by using the 1999-2010 Forest Inventory and Analysis (FIA) annualized data from plots in the Ozark Highlands of Arkansas and Missouri landscape. 

Results/Conclusions

Of the species groups examined in this study, the red oak group consistently dominated dead basal area as a proportion of the total basal area. Regionally, this mortality was significantly correlated with growing season PDSI with at 2- to 3-year lag behind single drought events, but at stand level, tree mortality was correlated mainly with tree crown class, tree diameter and competition.  Most of the hot spots of mortality occurred toward the central part of the Ozarks.