Tag Archives: valley oak

Searching For Another Blue Oak In Upper Las Virgenes Canyon Open Space Preserve

Blue oak-like leaves of an unusual oak in in Upper Las Virgenes Canyon Open Space Preserve (Ahmanson Ranch).

After the Ahmanson Blue Oak in East Las Virgenes Canyon died this Winter, I started to search for another blue oak (Quercus douglasii) in Upper Las Virgenes Canyon Open Space Preserve (aka Ahmanson Ranch). Blue oaks are rare at the southern limit of their range, but I was hopeful that if there was one blue oak at Ahmanson, there might be another.

Valley oak leaves in Upper Las Virgenes Canyon Open Space Preserve (Ahmanson Ranch).
Valley oak leaves.

Typically, blue oak leaves are noticeably different than valley oak leaves. The Jepson eFlora describes the leaf margins of blue oak as being more or less entire, wavy, or more or less lobed. The leaves of the Ahmanson Blue Oak fit this description. Valley oak leaves are usually much more deeply lobed and readily identified.

Recently, while on a run, I noticed an unusual oak near the top of a service road on the western margin of Lasky Mesa. Its leaves are not deeply-lobed and are a bit more dusky than the usual valley oak leaf. But the tree doesn’t look quite the same as the Ahmanson Blue Oak. One difference is that the shape of the leaves is not as uniform as those of the Ahmanson Blue Oak. This might be due to the wet 2022-2023 rain season and the flourish of leaves that resulted. And, as with the Ahmanson Blue Oak, this oak was burned in the 2018 Woolsey Fire, and its trunk is partially hollow.

Blue oak-like leaves of the unusual oak on the western margin of Lasky Mesa.
Blue oak-like leaves of an oak on the western margin of Lasky Mesa.

Based on its leaves, the “West Lasky Mesa Oak” could be a blue oak, blue oak hybrid, or valley oak hybrid. A 2002 study of a mixed stand of blue and valley oaks found that appearance can be misleading. When DNA tested, four of the five hybrid-appearing oaks in the study were not classified as hybrids. Of the four trees deemed most likely to be hybrids, only one oak was intermediate in appearance.

Although it seems unlikely this tree would have been overlooked, I could find no specific reference to the oak in the various studies and surveys done of Ahmanson Ranch. Please get in touch with me if you can provide additional information about this tree or how a DNA analysis can be arranged.

Some related posts: Ahmanson Blue Oak, Ahmanson Blue Oak Succumbs to Climate Change

Upper Las Virgenes Canyon Trailhead Valley Oak

Large valley oak near the Upper Las Virgenes Canyon Trailhead of Upper Las Virgenes Canyon Open Space Preserve (aka Ahmanson Ranch)

This large valley oak lives near the Upper Las Virgenes Canyon Trailhead of Upper Las Virgenes Canyon Open Space Preserve (aka Ahmanson Ranch). There used to be several large valley oaks near the trailhead, but they were killed in the 2018 Woolsey Fire.

The trunk of the Upper Las Virgenes Canyon Trailhead valley oak.
The brim of the cap is about 7 inches wide.

This tree is as large as any of the valley oaks I see along the trails at Ahmanson. I estimate it’s diameter to be a little under four feet. That’s not large by Northern California standards, but it is still a sizable tree. Valley oaks have a tougher time here.

Along with coast live oak, the valley oak is one of the iconic species of oak-grasslands at Ahmanson Ranch. In the past 20 years, valley oaks at Ahmanson Ranch have been more severely impacted by drought, fire, and rising temperatures than live oaks. In the not too distant future, the valley oak may become a relic at Ahmanson, much like the blue oak that died earlier this year.

Some related posts: Ahmanson Valley Oaks Finally Get Their Leaves, Ahmanson Valley Oaks Battling Drought, Ahmanson Blue Oak Succumbs to Climate Change, and Many More

Ahmanson Valley Oaks Finally Get Their Leaves

Cold weather delayed the leafing out of valley oaks at Ahmanson ranch until late March and early April 2023.

According to preliminary NWS reports, Downtown Los Angeles (USC) recorded average monthly temperatures well below normal in November 2022 and January thru March 2023. March was particularly cool, with an average high of about 64 degrees and an average low of about 50 degrees.

Besides high heating bills, Southern California’s unusually cold Winter affected several seasonal processes, one of which was when the valley oaks at Ahmanson budded and grew new leaves.

The leaves of valley oaks at Ahmanson Ranch typically turn in mid-December, and the trees usually begin to leaf out during the latter half of February. Depending on the tree’s microclimate, the emergence of new leaves may vary by a week or more.

Cooler than normal temperatures during January to March 2023 delayed the leafing out of these valley oaks in Las Virgenes Canyon.
Valley oaks in Las Virgenes Canyon in early April 2023.

The earliest I’ve photographed a valley oak at Ahmanson sprouting new leaves was February 3, 2015. Last year, a valley oak had new leaves on February 10, 2022.

The latest I’ve seen valley oaks sprouting new leaves is this year — from about March 20, 2023, in favored locations to April 4, 2023, in cooler areas such as Las Virgenes Canyon.

Prior to this year, the latest I’ve photographed a valley oak at Ahmanson with new leaves was March 9, 2009.

(Officially named Upper Las Virgenes Canyon Open Space Preserve, most users refer to the open space area as Ahmanson Ranch or simply Ahmanson.)

Some related posts: Revitalized Valley Oak at Ahmanson Ranch, Goldfields Are Blooming and Valley Oaks Greening, Valley Oak Leaf

Ahmanson Valley Oaks Battling Drought

drought-stressed valley oak in Upper Las Virgenes Canyon Open Space Preserve (Ahmanson Ranch)

Following four rainfall years in which Downtown Los Angeles (USC) has cumulatively recorded less than half of normal rainfall and accrued a precipitation deficit of more than 30 inches, many of the valley oaks at Ahmanson Ranch (Upper Las Virgenes Open Space Preserve) are drought stressed.

The most obvious signs of drought stress in valley oaks and many other plants are a reduced number of leaves and reduced leaf size. In severely stressed valley oaks the foliage has the appearance of a tree that is recovering from a wildfire.

At Ahmanson the degree of stress varies widely from tree to tree. The “TV tree,” an aesthetically-shaped and often-photographed valley oak on the west side of Lasky Mesa appears to be showing a higher than average level of stress.

Valley oaks and live oaks cohabit the oak savannas at Ahmanson Ranch, but live oaks appear to be more drought tolerant. The lone Blue Oak at Ahmanson seems to be doing OK and has at least as much foliage as it did last year at the same time.

Update January 15, 2021. “The Tree” died in the Spring of 2020, when Ahmanson was closed due to COVID-19. Although scorched in the Woolsey Fire, it never recovered from the 2011-2015 drought, and that appears to have been the primary cause of death.

Some related posts: Ahmanson Blue Oak, The Color of Rain IV