Category Archives: nature|trees

Rivas Canyon Eucalyptus

What is it? Photography by Gary Valle'.

These shallow channels looked like they might have been cut by a woodworker’s router. But they were cut — or I should say chewed — by Longhorned Borer beetle larvae, feeding on the cambium of a eucalyptus tree.

Fallen eucalyptus in Rivas Canyon. The grooves are from beetle larvae feeding on the cambium of the tree.
Fallen eucalyptus in Rivas Canyon. The grooves are from beetle larvae feeding on the cambium of the tree.

The tree was across the trail in Rivas Canyon. Not unlike the fallen oak on Rocky Peak, Southern California’s multi-year drought likely weakened the eucalyptus, making it susceptible to other pests.

The Rivas Canyon Trail connects Will Rogers State Park to Temescal Canyon. Today (and last weekend) I ran it as part of a long loop from the “End of Reseda” at Marvin Braude Mulholland Gateway Park.

Some related posts: Will Rogers – Temescal Loop, Will Rogers Western Ranch House, Downtown Los Angeles and San Jacinto Peak

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Fallen Oak

A large valley oak along Rocky Peak fire road that toppled following five years of drought.

The valley oak pictured above — one of the larger oaks along Rocky Peak fire road — toppled over in the summer of 2016 following five years of drought.

Fire and drought are a natural part of the valley oak’s habitat and the trees have evolved to withstand ordinary variations in their environment. However, severe fires or extended droughts, or fire in combination with drought can overcome the tree’s defenses.

The drought may have been the culminating factor in the felling of this oak, but fire and other factors may have also played a role.

Base of large valley oak along Rocky Peak fire road that toppled following five years of drought.
Base of large valley oak that toppled following five years of drought. Click for larger image.

According to the Fire Effects Information System (FEIS), the heart-rot fungus Armillaria mellea is usually present in valley oaks and larger oaks tend to be hollow or rotten in the center. The toppled oak was hollow near its base and its interior appears to have been blackened by fire. The FEIS describes instances where the decaying wood in the interior of older valley oaks could ignite in a fire, but leave the exterior bark uncharred.

What fire might have burned the tree? There are two possibilities: the 2008 Sesnon Fire and the 2003 Simi Fire. It probably wasn’t the Sesnon Fire — this photo of the tree, taken about a month after the Sesnon fire, shows little impact. I couldn’t find a photo of the tree following the Simi Fire, but photos taken nearby show a severely burned landscape.

Ultimately, it appears fire and drought weakened the tree, accelerating its heart rot and weakening its roots to the point it could no longer support itself.

Photos of the fallen tree are from this morning’s foggy run along Rocky Peak fire road.

Related post: Chumash Trail – Sesnon & Simi Fires

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Some Fall Color to Bring in the New Year

Some Fall Color to Bring in the New Year. Photography by Gary Valle'.

While much of the country shivers in the cold climes of Winter, the muted colors of the changing season have finally reached the lower elevation areas of Southern California.

Turning leaves of a willow in East Las Virgenes Canyon. December 28, 2017.
Willow in East Las Virgenes Canyon

In this area the leaves of Valley Oaks usually begin to turn around mid-December and the trees lose their leaves around the beginning of the new year. About a month and a half later trees begin to sprout new leaves, usually in mid to late February. From year to year the time frame can vary by as much as 2-3 weeks.

The photo of Valley Oak leaves was taken December 28, 2017 in Upper Las Virgenes Canyon Open Space Preserve (formerly Ahmanson Ranch). This willow in East Las Virgenes Canyon was also showing some nice color.

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