Oak trees are everywhere in Redlands — along Brookside Avenue, on the University of Redlands’ central quad, in private yards and on the wild lands in Live Oak Canyon. In good health, the trees give shade, provide habitat for wildlife, and connect Redlanders to our past.
Redlands Conservancy watches and worries about the condition of the oaks, which, in many cases, show evidence of significant stress. In the 15 years since 2004, eight old oak trees in what is now Herngt “Aki” Preserve have died and collapsed.
Field Ecologist Aaron Echols of Inland Empire Resource Conservation District examined the trees in Herngt “Aki” several years ago and said they were stressed by drought, not by disease.
The drought of the 21st century not only claimed several oak trees, it also prevented the trees from generating replacement trees.
Echols was surprised that he could find almost no indications of young oaks under and around the oaks in Little Live Oak Canyon.
Now, the California Forest Pest Council has issued another warning for oaks, this for the goldspotted oak borer (GSOB), which appears to be spreading in Southern California.
According to an August 2019 article, the GSOB was recently detected in Big Bear Valley in the San Bernardino Mountains and in other nearby communities.
The article said the new detection is significant since GSOB is a highly destructive invasive species that is devastating oak forests further south in San Diego, Riverside, Orange, Los Angeles and parts of San Bernardino counties.
The article says the “GSOB larvae kill trees by tunneling in the cambium and phloem, cutting off the photosynthate and starving the tree. The adults emerge from May through September, with the majority active from late June to early July.”
“Redlands Conservancy is concerned about this new threat as we have many large, old oaks in Herngt ‘Aki’ Preserve and at Redlands Gateway Ranch,” said Kathy Havert, the conservancy’s outdoor education coordinator.
Havert says that, according to Echols, most of the oaks on the land the conservancy manages range from 30 to 200 years old. According to the California Forest Pest Council, the GSOB is easily spread in firewood that is transported from one location to another.
It is spread through the movement of firewood and any other wood products when the bark is left intact because the late instar larvae and prepupae are located in the inner bark.
While the GSOB attacks primarily large red oak species, it also impacts coast live oak and California black oak, both of which are found in Redlands. The trees that are targeted are 18 inches and greater in diameter.
People who own or manage large oak trees in Redlands can look for definitive evidence such as D-shaped exit holes on the bole of the tree, produced by emerging adults after one year of infestation.
Twig dieback and crown thinning, which usually develops from top to bottom, are other indications of possible infestation, according to the California Forest Pest Council.
Redlands Conservancy encourages anyone transporting firewood to be aware of the possibility of spreading the goldspotted oak borer.
For more information and to see images of the GSOB, people may visit firstname.lastname@example.org
Threats to oak trees
Drought: Eight oak trees have died and collapsed since 2004, not from disease but from drought.
Insects: The trees could also fall victim to the goldspotted oak borer’s larvae that kill trees by tunneling in the cambium and phloem, cutting off the photosynthate and starving the tree, according to the California Forest Pest Council.