Red Oak Species Is Especially Vulnerable to Drought Events
Data from 6,997 Forest Inventory and Analysis plots were used to examine oak decline and mortality trends for major oak species in the Ozark Highlands of Arkansas and Missouri. Oak decline was greater in the red oak species whose values were three- to five-times higher than for white oak and nonoak species. In fact, the white oak group has maintained a relatively stable mortality rate that is comparable to nonoak species.
Analyses indicate that mortality in the red oak group was significantly connected with the growing season Palmer Drought Severity Index (PDSI) and usually lagged 2 to 3 years behind single drought events. PDSI is a measurement of dryness based on recent precipitation and temperature. Moreover, based on the past 17 years PDSI data, it appears that the cumulative effects of drought may persist up to 10 years.
The Ozark Highlands experienced a severe drought extending from 1998 to 2000 and another milder drought from 2005 to 2006. These drought events triggered the escalation of red oak mortality starting around 2000. Given that drought is a factor for increased mortality, forest resource managers should plan forest management activities to mitigate the effects of drought. Since older, denser stands have shown an increase in mortality, forest managers could increase forest age diversity.
During or immediately after future severe drought events, forest managers could elect to harvest trees that are more susceptible to mortality to avoid losses. Mortality rates increased further in the Ozark Highlands after the onset of a second drought event in 2005. Perhaps those trees were affected by the first drought event and did not have sufficient time to recover. Additional research could attempt to incorporate previous periods of drought into a model to predict the likelihood of mortality associated with sequential drought events because in the Ozark Highlands, drought has been shown to be an inciting factor that leads to increased levels of mortality.
Forest Service Partners