Danger lurks underground for oak...( WEST LAFAYETTE Ind. - Scientists try...)

WEST LAFAYETTE, Ind. - 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.

"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.

"Either the oak roots were much more nutritious and had higher energy content, or they contained fewer toxins, or some combination of those factors. Those are the main reasons an animal will choose one food item over another," Swihart said.

Swihart's study has been published in the current edition of the Canadian Journal of Zoology.

Under a variety of growing conditions, oak seedlings have comparatively high mortality rates, allowing other trees such as shade-tolerant maples and sun-loving, fast-growing tulip poplars to make up larger percentages of hardwood forests. 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
'/>"/>