By Kiara Gardner Bremner
I want you to imagine the lush green of oak trees, each branch twisting and reaching up to the sky; and then grounding themselves by extending back down to the earth, greeting each native grass and forb in their understory. The crowns of these oak trees are full of luscious green leaves, from evergreen to deciduous; and with a tremendous amount of diversity within species, these trees nonetheless hold the land around them. As keystone species and ecosystem engineers, they provide sustenance to the land, allowing the grateful acorn woodpeckers to forage while also giving structure to creeks that flow near and through them.
This describes many oak woodlands like those found in the Santa Monica Mountains, my childhood home, that consists mostly of oak trees like Canyon live oak and Coastal live oak trees. Both of these oak trees can host thousands of native insects that typically cause little damage to the tree itself, while also feeding and nourishing native bird communities in these Southern California oak ecosystems.
However, what happens when an invasive insect gets introduced to an oak ecosystem? Where birds can no longer prevent populations of this particular insect from expanding rapidly?
The canopy of these oak trees begins to fade from a lush green to a light brown, their bark starts to stain, and eventually, the crown of these trees begins to thin. The unfortunate reality of a severe infestation of the invasive insects called the Gold Spotted Oak Borer (GSOB) is a devastating increase in the number of oak fatalities unless GSOB is caught early and properly managed. This is the harsh reality of many oak woodlands and savannas in the southern California region where Climate change can make trees more susceptible to invasion due to drought; while the movement of infested oak firewood throughout southern California spurs on the spread of this insect.
However, there are ways to halt the spread of GSOB, where groups like Mountains Recreation and Conservation Authority(MRCA), UC ANR, TreePeople, and Fire Safe councils focus on education, mitigation efforts, and preventative measures to stop the spread of invasive insects into areas like the Santa Monica Mountains.
TreePeople teaching the Santa Monica Mountains Fire Safe Council how to identify and survey for GSOB on oak trees.
Treepeople are at the forefront of GSOB research and education; and as a member of the Santa Monica Mountains Fire Safe Council and as a concerned community member, I was able to join a GSOB survey training hosted by TreePeople and accompanied by AmeriCorps, California Climate Action Corps, and Tiuvac’a’ai Tribal Conservation Corps members. At this training we hiked throughout the oak-filled mountains of Rice Canyon in Los Angeles County; where my coworker and I were taught a plethora of knowledge on the GSOB lifecycle; as well as how to survey and identify a GSOB infestation, and finally, how to stop the spread of GSOB. Here is what I learned:
The Gold Spotted Oak Borer’s (GSOB) Lifecycle:
The adult GSOB will lay its eggs in the bark of an oak tree
The eggs will then hatch into its larval form, where the larvae will bore into and heavily feed on the inner cambium of the tree; cutting off its water supply.
The larvae will go under a metamorphosis into pupae, where they will make their way to the outer bark
GSOB will then emerge as an adult and fly to another tree to complete that process over again
The GSOB life cycle takes a full year to complete
How to identify GSOB:
Trees that are most susceptible to GSOB infestation are Coast Live Oak, Canyon Live Oak, and Black Oak trees
First indication of a GSOB’s presence is a D-shaped exit hole that is around 3-4mm, that will normally be concentrated on the base of the trunk moving upwards depending on how infested the tree is
The Gold Spotted Oak Borer beetle in its adult form is 10mm long and as its names indicates has gold spots along its wings, and an iridescent green exterior
As mentioned before, when finding severely infested trees with multiple exit holes it will usually be accompanied by:
○ Crown thinning
○ Dark black/red bark bleeding or staining
○ Dying Branches with light brown leaves
○ Woodpecker Foraging
An example of tree staining on the left and the GSOB’s D-shaped exit hole highlighted in purple marker on the right.
How to Stop the Spread of GSOB and what to do next:
Spread of GSOB can be mostly attributed to the movement of infested firewood, where GSOB does not spread long distances by themselves. Therefore, for safe practice follow the phrase, “buy it where you burn it”. This means buy firewood locally and burn it in the area you bought it from, as GSOB can be within the bark of your firewood and can be spread from the firewood to a tree; potentially infesting a new region.
If spotted you can submit a form to UC ANR to inform local authorities that GSOB has been found in your community, for more information visit this link.
Research is still on-going into mitigation efforts and the biology of GSOB, where community-based solutions are at the forefront from having local eyes on trees to identify infestation, while local land managers are looking into the benefits of cultural burning practices in La Jolla Reservations as well.
Despite this being a serious issue with heavy repercussions, the training with TreePeople showed me that even in dark circumstances there is still plenty of room for laughter and fun. A day out in the field with TreePeople was not only educational, but inspiring, it really showed me that passionate and empathetic people who care about the environment around them and want to protect their home just like I do, are out there doing the work on the ground. It's comforting to know that in the face of adversity and large-scale problems like climate change and invasive species, that community can elicit hope and compassion for the environment and others around you.
Work Cited:
Cleveland National Forest - Home. Forest Service National Website. https://www.fs.usda.gov/detail/cleveland/home/?cid=stelprdb5279813
University of California, D. of A. and N. R. Report goldspotted oak borer symptoms. University of California, Agriculture and Natural Resources. https://ucanr.edu/sites/gsobinfo/What_You_Can_Do/Report_GSOB_Symptoms/
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