City Creek Nature Notes – Salt Lake City

October 1, 2016

October 1st

The Secret Language of Gambel’s Oaks

10 a.m. Light, weather, and other mysterious factors that speak a secret language known only to the trees of the Gambel’s oak woodland has caused those oaks’ leaves to turn. In just one day, between two to five percent of all the leaves on all Gambel’s oaks in Pleasant Valley have turned or are beginning to turn. This change is too coordinated and too purposeful to not involve communication. Do the oaks exchange chemical messages as the delicate ends of their roots intertwine underground? If so, how does this explain that clusters of oaks far removed from other oaks in the center of the meadow have also changed? Do these oaks exchange some scent, too faint for the human nose to detect, by which they all agree that it is time to go to sleep?

The leaves of the Gambel’s oak do not turn medium brown color in the same way that horse chestnut trees turn. The chestnuts at the Guardhouse gate turn brown from the outside in. The maples turn a uniform red and others a uniform yellow, and then their leaves fall to the ground. At mile 1.5 at the southwest end of Pleasant Valley, Gambel’s oak leaves first brown and curl at the outermost tips. Then suddenly, the whole leaf turns.

Paradoxically, at the northeast end of Pleasant Valley at mile 1.7, the Gambel’s oak leaves first develop brown spots distributed uniformly over the entire leaf. These grow, the leaf edges turn, and then the entire leaf goes. Around the bend in the road at mile 1.8, these spots also cover the red leaves of maple trees, but such spots are absent from both the oaks and maples lower in the canyon near the guardhouse. On closer inspection, the spots are raised dollops of infection, either fungal or bacterial, growing on the leaf surface. As the leaves turn, the leaves become susceptible to infection, and succumb. Also at the northeast end of Pleasant Valley are two crab apple trees, probably planted by the early Mormon pioneers. They are still green, healthy, and free of spots of infection.

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