The bronze sculpture, installed in 1993, symbolically depicts a scorched eucalyptus tree and the new growth that came into the fire zone after the deadly blaze.
It was designed by artist Gail Fredell and built by volunteers, Piper said.
Piper said that on Tuesday, he noticed that four of the branches on the sculpture in the Firestorm Memorial Garden at Tunnel Road and Hiller Drive in Oakland had been bent.
On Wednesday, he found that two more branches had been bent and filed a police report.
When he visited the sculpture late this morning, he found that eight branches had been sawed off. One branch was lying on the ground near the memorial, but the other seven were gone.
He said he found marks on the walkway from what looked like heavy equipment that had been brought in, and saw marks on the memorial itself where the branches had been severed.
"It's an insult to the 25 people who lost their lives in the fire," Piper said.
The fire, which tore through the Oakland Hills on Oct. 21, 1991, killed 25 people, injured 150 others and destroyed more than 3,500 homes, Piper said.
Today's vandalism was not the first time the memorial sculpture has been damaged, but it is the most severe. In the past, vandals have bent branches, but this is the first time anyone has managed to remove them.
Piper said the Landscape Committee is evaluating what to do next.
They community-based committee is accepting donations to cover the cost of creating new custom-designed branches for the sculpture. Checks can be made payable to Friends of Oakland Park and Recreation and sent to 33 Hiller Drive, Oakland, CA 94618.