El Palo Alto, the city's iconic redwood that has stood near the banks of San Francisquito Creek for more than 1,000 years, is undergoing the most in-depth technical study of its health ever done, city Urban Forester Walter Passmore said.
The study is using cutting-edge radar technology to see deep into the tree's core and to assess its roots. The work is being donated to the city by Arborist OnSite, a South Bay horticultural consulting company, Passmore said.
A scan of the trunk's outer layers started Thursday, July 25, and was expected to be finished by the end of the afternoon. Dave Dockter, the city's managing arborist, donned a hard hat and harness and prepared to rappel down the 25-foot-deep bank of San Francisquito Creek Thursday morning. Every three feet or so he would aim the radar gun at a concrete retaining wall Jane Lathrop Stanford had installed in 1903 to keep the bank from eroding further.
The radar technique is like magnetic resonance imaging, or MRI, and will check the soundness of the wood and the volume of the roots in the soil. The equipment fits into two small hard-shell suitcases. Only two units exist in California, and there are only 12 in the U.S., Bob Booty of Arborist OnSite said.
A March assessment of the tree found some decay but also held promising news.
"The very top of the tree is dead," Booty said. But the buttress roots at the bottom of the tree are in very good health, he added.
Arborist OnSite and city arborists also plan to scan the trunk at about 14 feet high, Booty said.
El Palo Alto had twin trunks in 1875, when it marked the corner of Leland Stanford's farm, but in the 1880s one trunk disappeared. Some people theorize it was swept away in a flood; others think it was removed because it was too near the Southern Pacific railroad bridge, Passmore said. Whatever the reason, Leland Stanford added a wood bulkhead along the creek to stabilize it.
The barriers of wood and concrete will be no obstacles to the ground-penetrating radar, which will map deep into the soil. It will record the different densities of materials to determine where the root system occurs and its condition. Passmore said the roots could run all the way down to the creek floor or deeper at least 25 feet.
At 1,073 years, El Palo Alto is middle-aged. In 1999, the tree trunk was 90 inches in diameter and 110 feet high, according to a report by Dockter. At that time it had a crown spread of 40 feet.
But the tree has shrunken since its recorded height of 134.6 feet in 1951.
The tree is actually healthier than in previous times, Dockter said. Wells that once sucked up groundwater were capped in the 1950s, allowing more water to reach the roots. The city in the 1950s also added a mister to the top of the tree to simulate the redwood's natural fog environment, he said.
El Palo Alto has survived centuries of flood and drought, changes to the creek that feeds it, and pollution and particulate matter from vehicles. Standing just a few feet from both the creek and the railroad bridge, its foliage was once affected by belching locomotive engines, Passmore said.
The proposed high-speed rail system could also further affect the tree.
"Trains make wind when passing by that will blow branches and leaves. The high-speed trains might not be able to use the exact footprint of the existing rail, and that might infringe on the tree's root zone. There are a lot of possibilities we need to be cognizant of," he said.
El Palo Alto is something of an anomaly. Coast redwoods are typically found in moister, foggier environments than Palo Alto.
"It's not common to have redwood trees in the dry environment we have in Palo Alto," Passmore said.
Standing on the footbridge over San Francisquito Creek, he marveled at how the tree came to be there and survived the centuries.
"It was probably a flood that brought its seed down from the mountains, where it was deposited on the creek bank," he said.
El Palo Alto has been a part of many major events in local history. Named by the Spaniards, it means "the tall tree" (literally "stick"). Spanish explorer Gaspar Portola camped under the giant tree during his 1769 expedition. It is designated as California State Landmark No. 2.
"This tree symbolizes the pioneer spirit of Palo Alto," Passmore said, noting the people and historical milestones that have come before and are likely to continue gravitating to Palo Alto in the decades to come. He thought of Stanford and the late Silicon Valley icon Steve Jobs and others who have put down roots in the valley.
El Palo Alto established itself on the banks of the creek before any of them, and it endured in an often hostile and challenging environment.
"It's that type of fighting spirit that exemplifies the spirit of Palo Alto," he said.
A video of the work will appear on the city's website in the future.