Horses and oak trees are harmful to each other. Horses should not eat new leaves and ripe acorns of oak trees. Horses under the canopy of oak trees can do severe damage to the trees.
With the heavy acorn crop this fall, now is the time to keep your horses away from oak trees. Although considered a moderate risk, according to Equus magazine, "Oak trees contain an astringent that kills cells in the digestive tract and kidneys of horses. Ripe acorns and new leaves are toxic to horses, but intake of large amounts of either can be deadly." For more information visit http://www.vth.colostate.edu/poisonous_plants/
The most likely effect to the tree of having horses under oaks is compaction of the soil due to the weight concentrated on the hooves. The compaction from any heavy activity under the tree can suffocate the roots, as they lie a mere 12 inches beneath the surface of the soil. Other threats include injury to the crown (the flare of the trunk as it enters the soil) and chewing the bark. Keep in mind that our trees are probably already under stress due to human activity and drought, and one more stress may be too many.
The most effective way to keep horses and oaks far enough away from each other is to fence around the tree to the end of the drip line (the canopy or farthest reach of major branches). The tree can still cast a cool shadow on hot days without risk to either our precious horses or our magnificent trees.
If you are interested in learning more about oak trees, contact Friends of the Oaks (FOTO) at 821-1904.