FIA Report on Oklahoma’s Forests

2015 Update shows High Oak Mortality

pine plantation
Dieter Rudolph, of Oklahoma Forestry Services, surveys a pine plantation. Photo by Carri Abner, FIA coordinator.

Until 2009, the U.S. Forest Service’s Forest Inventory and Analysis had never surveyed Western Oklahoma. “Western Oklahoma has some forests, but very little timberland,” says SRS forester Kerry Dooley.

Land that produces timber – at least 20 cubic feet an acre, each year – is considered timberland. Timberland is plentiful in Eastern Oklahoma, and FIA has surveyed there since 1936.

Oklahoma is the 20th largest state in the U.S., and covers almost 45 million acres. About 12 million acres are forested, and the rest includes grasslands, farms, lakes, cities and neighborhoods.

“In Oklahoma, 7.1 million acres of forest land qualified as timberland,” says Dooley. The 5.2 million acres of other forest land are not ideal for timber extraction. However, all natural areas can provide wildlife habitat, recreation opportunities, and ecosystem diversity.

In 2015, FIA and the Oklahoma Forestry Services sampled 5,529 plots across the state. Dooley summarized their findings in a recently published Resource Update. Dooley also contributed to a Resource Bulletin that describes findings of the 2014 forest inventory.

From east to west, the Oklahoma landscape changes dramatically. “Southeast Oklahoma is the wettest and the hilliest – lots of pine,” says Dooley. “In the rolling uplands of central Oklahoma, oak and hickory forests are common, while 98 percent of the panhandle is not forested.”

Ouachita Mountains of Oklahoma
The Ouachita Mountains cover much of southeastern Oklahoma. Photo by Okiefromokla.

The panhandle receives less than 20 inches of rain each year, and trees that grow there are more typical of the Western U.S. than the South.

The vast majority of Oklahoma forests are naturally regenerated. However, loblolly and shortleaf pine forests are artificially regenerated about half the time. Most pine forests are located in Southeast Oklahoma, where over half the land is considered timberland.

Eighty-three percent of forest land is owned by individuals and nonindustrial private owners. However, loblolly and shortleaf pine forests are the exception – nonindustrial private owners own 40 percent of loblolly-shortleaf pine forests.

Loblolly pine and shortleaf pine are common, especially in the southeast. Other common species include post oak, winged elm, American elm, eastern redcedar, and hickory. During the 2015 survey, FIA recorded 76 tree species across the state.

Together, these trees and others take up 9.6 billion cubic feet– about the size of 230 Houston Astrodomes. Post oak accounted for 22 percent of this volume, and shortleaf and loblolly pines were the next big contributors.

Black oak (Quercus velutina)
The net growth rate of oak trees, including black oak, declined. Image courtesy of Wikimedia Commons.

Oaks showed a troubling drop in net growth rates. “Starting in 2011, the net growth rate in Eastern Oklahoma began declining,” says Dooley. “Post oak and red oaks were hit especially hard.” The red oaks include northern and southern red oaks, black oak, Shumard oak, and others.

Red oaks only represent 12 percent of the total volume of living trees. However, the red oaks account for 37 percent of the mortality volume.

“Disease appears to have killed most trees,” says Dooley. “However, it’s common for multiple factors to contribute to a tree’s death.” The FIA field crews noted many causes in their field notes. The notes also showed that Hypoxylon canker was the suspect behind most tree deaths.

The fungus that causes Hypoxylon cankers can linger in wood and bark for years, and is most dangerous when trees are already stressed.

“The trees that succumbed to disease may have been affected by other stressors,” says Dooley. “Surveys in the coming years will help shed light on whether the heavy oak mortality was a short term event or is a continuing trend.”

Read the full text of the update.

For more information, email Kerry Dooley at kjdooley@fs.fed.us.

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