Oak mortality and decline events have been recorded in eastern US forests since 1856. It has impacted upland oak-hickory forests, particularly species in the red oak group (Quercus Section Lobatae). Drought is a common inciting factor in oak decline, while advanced tree age is considered a predisposing factor, and organisms such as armillaria root fungi and opportunistic insects are believed to contribute. Declining trees are initially indicated by foliage wilt and browning followed by progressive branch dieback. If crown dieback continues whole trees can die. Long term forecasts for this region indicate increasing susceptibility to oak decline. For instance, forests are aging while periodic droughts are expected to increase in frequency and intensity across portions of the region thereby exacerbating susceptibility to oak decline on millions of hectares of forest. In the Ozark Highlands alone over 60.5% of red oak dominated forest had been severely impacted by oak decline during the last major oak decline event. In this talk we synthesize our research on oak decline in the eastern US, examining its occurrence, distribution and dynamics. Methods include intensive inventories at seedling and forest stand scales, and utilizing Forest Inventory and Analysis data for landscape and regional scale modeling.
Results/Conclusions
Within one year of oak decline onset at the stand scale the number of standing dead northern red oak (Quercus rubra L.) trees significantly increased by 55% (p=0.029). Across the 6.0 million ha forested landscape of the Ozark Highlands 3.6 million ha of northern red oak, 0.4 million ha of white oak (Quercus alba) and 0.28 million ha of non-oak dominated forests had severe oak decline between 2006 to 2010. While model simulations across a 0.43 million ha area through the next century predict a reduction of potential oak decline sites by 25% if historic fire frequencies are re-established. However simulations resulted in only a slight improvement by harvesting alone resulting in only a reduction of 3% of high risk sites over doing nothing. A larger regional analysis of eleven states indicates that red oak had 7% greater crown dieback than white oak during 2003 to 2010 following drought.
Results from our research suggest methods for managers to improve the resilience of oak dominated forests faced with increased risk of mortality due to oak decline in the Eastern United States. Potential decline management methods include mimicking historic disturbance, encouraging resistant species and managing physiological age of susceptible trees.