Oct. 20, 2016 — COLLEGE STATION, Texas — Post oak trees across the state are facing higher mortality rates in both urban and rural settings.

After the 2011 drought, a higher mortality rate in many trees was to be expected but Texas A&M Forest Service sought to determine if the post oak population did have a higher mortality rate in their natural, rural environment.

In order to determine the true mortality rate Texas A&M Forest Service compared the mortality rate of post oaks with two other tree species utilizing data from the Forest Inventory and Analysis Program (FIA), the nation’s forest census. Eastern redcedar and cedar elm were chosen because of their similar habitat ranges and drought tolerances.

Texas A&M Forest Service discovered an increase in the mortality of mature post oaks. Between 2006 and 2011, there was a 30 percent increase in post oak mortality, while the other two species maintained their mortality rates. After the 2011 drought an 88 percent increase in post oak mortality occurred. These numbers would not be a subject of concern if the regeneration of the post oak in its natural habitat was thriving, but data shows a decrease in the number of returning post oaks, while there was an increase for eastern redcedar and cedar elm. Post oaks are dying at a rate of 1.2 times the mortality rate of other trees in East Texas.

“With FIA data, we are able to compare different tree species and how their populations change over time,” said Texas A&M Forest Service Geospatial Analyst Rebekah Zehnder. “One of the many variables that FIA tracks is tree mortality, which allows us to see that post oak mortality has increased in the past 10 years.”

The loss of post oaks in urban areas can be easy to explain as they are a low-tolerance tree and prefer to be undisturbed in their native habitat. When soil disruption takes place within the roots of post oaks they typically become stressed and begin to show symptoms of decline immediately, leading to death within six years.

Drought and lack of natural fire are two main reasons for the decline in the rural post oak population. Because post oaks are intolerant of shade and competition, they typically grow in savannahs or forests adjacent to grasslands. Once established, post oaks require a fire regime to keep competition low. According to the Texas A&M Forest Service online drought application, in most years from 2005 to 2015 over half of Texas’ forest land was abnormally dry during the months of September to November. Not having adequate soil moisture during that time of year could prevent post oaks from germinating, which could explain a portion of the decline in the number of post oaks returning to the landscape.

The post oak root system is sensitive to disturbance, so many commercial growers do not offer potted trees. Because of this, Texas A&M Forest Service recommends planting acorns to bring back your post oak population. The best acorns for planting have recently fallen from their parent oak tree beginning in late September and continuing to mid-November. Once the acorns have been collected, the caps should be removed and the acorns should be soaked in water for 48 hours. Planting sites should be in full sunlight with loose-loamy sand in an area that allows water to drain well. Place three to four acorns on their side in a 3-inch deep by 6-inch wide hole, and cover with approximately 1-inch of soil, with a thin layer of mulch on top. The acorns should be watered once a week if rainfall is absent and seedlings should emerge in 10 to 45 days. Once the seedlings have reached 4-inches tall, and have at least four true leaves, select the healthiest seedling and remove the others.

Join Texas A&M Forest Service Staff Forester Zaina Gates for a Facebook Live event tomorrow, Oct. 21 at 10 a.m. Gates will be discussing the higher mortality rates of rural post oaks, the causes and how to plant post oak acorns. She will also answer questions from viewers.

Visit the Texas A&M Forest Service Facebook  and follow us to receive notifications about the Facebook Live event.

For more information about drought in Texas and the FIA program visit the Texas Forest Information Portal.

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Contacts

Zaina Gates, Staff Forester
979-458-3151, zgates@tfs.tamu.edu

Texas A&M Forest Service Communications
979-458-6606, newsmedia@tfs.tamu.edu