For me, the term “dog days” evokes an image of Al Pacino sweating it out in the bank holdup in “Dog Day Afternoon.”

For some, the term implies dogs lying in the shade, panting to cope with the summer heat.

The term actually refers to Sirius, the Dog Star.

Here in the Northern Hemisphere, Sirius rises near dawn at this time of year. It is the brightest star and you can find it by imagining a straight line downward through Orion’s belt. It points to Sirius. (Not being much of an astronomy buff, I had to look it up.)

Observing the stars is a grand way of noting the orderly procession of the seasons.

Here is another way to note seasonal change, as well as the condition of certain trees:

Lammas shoots. Lammas is an old Anglo-Saxon term for the day designated to celebrate the wheat harvest, Aug. 1, “a day to sit around a fire and sing songs,” so it says in Wikipedia.

Here in Northern California, Lammas shoots are noticeable as a flush of new, light-green growth in the outer canopies of vigorous valley oaks. Conversely, the lack of Lammas shoots is a sign that the tree is not in the best of health.

With the effects of ongoing drought, I have been seeing plenty of that this year.

Last week, I noticed another visual clue of dog-days drought stress in local trees: Driving along Howell Mountain Road toward Conn Valley Road, I noticed large expanses of blue oaks all turning yellow and going dormant.

This species, among our California native oaks, is best adapted to summer drought. Its strategic mechanism for survival in drought is “desiccation avoidance” (“Arboriculture,” Harris Clark, Matheny, 2004).

In various trees and plants this strategy may include conserving internal moisture, storing water in fleshy roots or stems, deep, wide-spreading roots, leaf adaptations that reduce water loss — like early shedding — and other adaptations.

In contrast, most of the trees planted in local landscapes are more susceptible to damage and decline from drought stress.

I noticed examples of this in my neighborhood this summer in a nice new landscape. The owner had two coral bark Japanese maples planted in the front yard within the past year. Both trees began showing yellow-orange foliar color, very similar to normal fall color, but beginning around July.

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It’s a good bet that those two trees are on an automatic drip irrigation system that is delivering barely enough water to keep the trees alive.

Even drought-tolerant tree species may be severely damaged by drought, especially in young transplanted trees that have not yet developed mature root systems.

As drought continues trees may undergo physical damage, like leaf scorching, sun injury to bark, and cavitation — internal interruption of the life-sustaining column of moisture connecting the roots to the leaves. Visible results appear as dead bark with fungal fruiting bodies, and dead branches.

Compounding the stress, natural defenses go down and trees become susceptible to opportunistic diseases.

In a recent seminar at UC Davis on wood decay, Dr. Jim Downer, UC Cooperative Extension, Ventura County, commented that Botryosphaeria, one of these opportunistic fungal infections, is wreaking havoc in Southern California. He said, “You’re lucky up here in Northern California. It’s turning into a wasteland down there.”

Last winter’s more normal amount of rainfall here was certainly welcome, but not a cure-all for damage that has been inflicted over several years. Trees need time and moisture for recovery. And they cannot “heal” dead or dying parts.

The best we can do is to be familiar with the needs of the trees under our care, and take appropriate action to save them if we can.

Bill Pramuk is a registered consulting arborist. Visit his website, www.billpramuk.com, email questions to info@billpramuk.com, or call him at 707-226-2884.

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