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Danger Under Oak Seedlings03-10-09 | News

Danger Under Oak Seedlings

Scientists trying to understand why oaks are starting to disappear from North American forests may need to look just below the surface to find some answers.

Purdue University researcher Robert Swihart found that pine voles, small rodents that live underground, prefer oak roots to those of other commonly growing seedlings. The study identifies the rodents as a possible factor leading to high oak mortality rates that are threatening the resource base of the hardwood industry.

The loss of oaks would have other serious effects besides losses to the hardwood industry. Oak mortality could reduce the capacity of hardwood forests to support wildlife populations that rely on oaks for food – everything from deer and turkey down to mice and songbirds.

“You see a lot of mature oaks, but you don’t see a lot of oaks in the understory beneath the canopy. If you don’t see them there, you won’t see mature oaks in 20 to 30 years,” Swihart said. “We are facing a period in our history that could lead to a great crash in oak availability.”

Swihart offered pine voles a selection of tree roots to eat in the laboratory, and they overwhelmingly gravitated toward oak roots. Voles caused more than twice as much damage to white oak roots than northern red oak and black cherry, and more than six times more damage to white oak than black walnuts. The voles snubbed yellow poplar roots altogether.

Most of the studies on why oaks have a hard time regenerating have focused on competition from other seedlings, the use of acorns as food for small animals above the ground and the use of oak seedlings as food for deer. There is little overall loss of oak forest to date, but that might change if foresters, the timber industry and landowners do not implement practices that better manage long-term oak growth and development.

Purdue undergraduate student Leslie Schreiber worked with Swihart on the pine vole study. Funding for the work came from Purdue Agriculture.