Over the five-week winter break, Facilities Management staff removed trees from the deck around the Arthur G. Coons Administrative Building (AGC), Sycamore Glen and outside various academic buildings. Facilities removed some trees that were unhealthy and others as part of an ongoing plan to remove invasive species and introduce more native species to campus.
“Last spring we had a large tree come down, and it sparked an investigation where I had to have consulting arborists come out and assess the threat level of some of our larger, older trees,” Grounds Supervisor Thomas Walters said.
During the Spring 2017 semester, a tree fell onto a car and came close to hitting the Tiger Cooler. After inspection, Facilities determined that the surrounding pavement had cut off part of the tree’s root system, destabilizing it. According to Sustainability Coordinator Jenny Low, Facilities then removed disease-ridden trees and began to consider what other trees could be a safety concern.
Low said that during the drought the school reduced irrigation to the trees, leading them to become water-starved and unable to fight off pests. Facilities removed several diseased trees from areas where they could pose a threat to student and faculty safety.
According to Walters, the climate in Southern California poses a challenge to tree maintenance on campus. Facilities has to constantly monitor the trees, and they do not always live their full lifespan without supplemental nutrients and care.
Biology professor Gretchen North said a species of beetle called the Polyphagous Shot Hole Borer has recently become a serious threat to trees across Southern California. On campus, it poses the greatest threat to the sycamores. Facilities has already removed several infected trees, but North said it is likely that more will need to be removed to prevent the fungus from spreading to neighboring trees.
“[The beetles] don’t just make holes in the trees, they deliberately bring in these fungal spores and cultivate the fungus in the tree, so it’s really insidious,” North said.
According to North, there is no treatment to deter the beetles or prevent the spread of the fungus. She added that research teams and several students in the biology department are trying to find one. Facilities is trying to keep the remaining trees healthy through deep watering and additional nutrients so they can better resist invasion by the beetles.
In addition to ongoing tree maintenance and preventing the spread of beetle infestations, Facilities is working with Van Atta Associates, Inc. and the biology department on a long-term project to replace invasive trees in Sycamore Glen with native trees such as Coast Live oak. These types of trees can sustain themselves in the Southern California environment, Walters said.
“We are trying to reestablish native trees — trees that would be most beneficial to native birds, native pollinators and basically give an appreciation for the habitat as it would be if Oxy wasn’t here,” North said.
North, who works alongside Walters and the consulting arborists, said that her main goals are to be as wildlife-friendly as possible while remaining sustainable and conscious of water use. She said that the school is choosing drought tolerant, fire resistant and aesthetically pleasing native trees to replace removed trees. The tree species that they targeted for removal were eucalyptus and tree of heaven, both of which are invasive species.
“[Eucalyptus] tend to interfere with the establishment of native species partly because they drop their leaves that have so many chemicals that inhibit the germination of other species,” North said.
North added that eucalyptus, which grows quickly, is weaker and prone to falling. It is also a fire hazard. Facilities removed the tree of heaven because it also grew quickly and outcompeted native trees for resources and space.
In Sycamore Glen, Facilities removed 21 trees. According to North, the tree removal process was minimally invasive and did not disrupt local wildlife.
With the invasive trees removed, Walters said that the next phase is to replace the trees with other species. Candidates include coast live oak and a variety of native walnut. He estimates that around 50–100 trees and shrubs will be planted.
“From where it stands now, it’s a lot easier to figure out what plants we want to put back in because there is a fair amount of California native trees and shrubs that we are choosing to try and fill that space back in with the largest amount of wildlife possible,” Walters said.