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Arroyo Seco Foundation

News of the Arroyo


Citing Safety, City Moves to Cut Down 65 Trees in the Central and Lower Arroyo





August 13, 2015 — The City of Pasadena is moving forward to combat unsafe trees in the Arroyo Seco by finalizing plans to remove 65 California sycamore trees diagnosed with a serious beetle infestation just weeks after a 75-foot pine toppled over injuring eight children in Brookside Park.


Rachel Young


Pasadena Now


An invasion of Polyphagous Shot Hole Borer wood-boring beetles has swept through sycamore trees in the Arroyo Seco, officials said. The beetle's "galleries" (tunnels) are shown in the photo above at left. Those galleries weaken the tree to the point where limbs simply fall off, creating a significant danger to the public. (Images: City of Pasadena)

The City of Pasadena is moving forward “aggressively” to combat unsafe trees in the Arroyo Seco by finalizing plans to chop down 65 California sycamore trees diagnosed with a serious beetle infestation just weeks after a 75-foot pine toppled over injuring eight children in Brookside Park.

That July 28 tree collapse in the Central Arroyo just out Kidspace Children’s Museum resulted in a frantic, heart-stopping televised search by police and fire personnel hunting for children who might be underneath the large limbs.

In the end, six children sustained moderate injuries and two were rushed to USC in critical condition. They have both recovered.

The cause of the pine tree’s collapse has not yet been announced by the City.

Last night, a City commission heard plans to cut down the sick sycamores in what would be the second-largest tree cutting event within Pasadena in recent memory.

In 2013, the City partnered with the Arroyo Seco Foundation to monitor an invasion of beetles which can devastate trees and leave them fragile and unsafe.

The Polyphagous Shot Hole Borer (PSHB) beetles that spread into California in 2003 eat through the trunk of a tree and leave tunnels, called galleries, around the center of the tree.

“These galleries weaken the wood of the trees and make them very unsafe which is why we are aggressively trying to remove the trees,” Darya Barar said, an arborist for the City of Pasadena. “So that the safety of the public is maintained.”

The largest safety concern lies in lateral branches that simply break off mid-branch and plummet to the ground because the structure of the tree has been damaged.

“Out of nowhere a big branch could just detach,” Forestry Superintendent Kenneth Graham said. “It’s a sad thing to do to have to remove this many trees, but I see it’s warranted. If you go down there you will see downed branches that detached for no apparent reason.”

The 65 trees were deemed to meet the threshold for removal after a recent follow-up inspection that swept the east and west sides of the Arroyo channel from the San Pascual horse stables in the south to the Rose Bowl in the north.

“Anywhere past the Rose Bowl we haven’t inspected yet,” Graham said.

Also out of a concern for safety, the City ordered tree trimmers into Brookside Park during the first week of August to minimize potential danger to the public from falling tree limbs.

Arborist George Salinas of the George Salinas Tree Preservation (GSTP) company fielded a team of eight men trimming all the trees in the area outside Kidspace Museum except for sycamores.

Salinas said at that time that although most of the trees he had seen so far looked healthy, many of the trees had full and heavy branches that badly needed trimming.

“The end of the limbs were drooping down —we took a lot of the weight off so the trees should be safer,” Salinas said.

Before the trimming in early August, the trees in Brookside Park were last trimmed in April 2011 according to City information officer William Boyer.

Graham indicated that many trees in the Arroyo Seco would continue to be monitored for the infestation, but had not met the threshold for removal.

Since last fall the Arroyo Seco Foundation has sent 30 volunteers out as a “citizen science project” to monitor the movement of the shot hole borers in the entire urban forest within the city.

Through a mobile phone app called Esri’s Collector for ArcGIS, the volunteers have recorded the type of tree, whether an infestation is present and the diameter. One of the tell tale signs of the disease onset is that the tree sweats in an attempt to excavate the beetle.

“The Shot Hole Borer is a very serious issue. We’re in the process of reviewing the 65 trees and we don’t have any comment at this time, but we are following this,” Scott Cher of the Arroyo Seco Foundation said.

Arroyo Seco Foundation Director Tim Brick said he was unaware that the City is planning to move ahead with the tree removal.

“We have been partnering on monitoring the damage by the shot hole borer — that’s all I’m going to say right now,” Brick said.

The PSH beetle infests over 110 host species, including common native trees found in Arroyo parks such as big leaf maples, box elders, white alders, California Sycamores, Fremont cottonwood, and several variety of oaks.

“It’s too bad, especially the [sycamores] along Arroyo Boulevard going toward the aquatic center. I remember when you planted them and they grew so beautiful and grew so fast. And then this hits them,” Urban Forestry Advisory Committee Chair Emina Darakjy said during Wednesday’s meeting.

The City will plant replacement trees in the fall of varying species that are not friendly homes to the hole boring beetles. The plant communities outlined in the Arroyo Seco Master Plan will guide the selection of species.

“Our Public Works crews are out there every day tending to Pasadena’s Urban Forest. They are constantly inspecting trees, responding to citizen requests and other city field staffers who may spot something — we all love our trees,” Boyer said.

To find out more about the survey conducted by the Arroyo Seco Foundation and their efforts to stop the spread of the infestation visit




Arroyo Seco Foundation, 570 W. Avenue 26 #450, Los Angeles, CA 90065-1011
PO Box 91622, Pasadena, CA 91109-1622 (323) 405-7326