Oakland can't say how old it is, just that it plans to cut down the tree by the end of the year. The tree's advocates say it could be 500 years old.

"I can see it's no longer a healthy situation for this tree," said Sue Morgan, a Glenview Elementary School teacher and education director of Friends of Sausal Creek, a volunteer group dedicated to improve the watershed.

Morgan frequently takes students to visit the oak, telling stories of its history and how trees in Dimond Park fit into the ecology of Oakland and the Bay Area. She knows it's the tree's time to go but was upset Tuesday when she came upon city crews with chainsaws.

Located next to a structure known as the scout hut near the end of Wellington Street, the Champagne Oak was called possibly one of the oldest oaks in the country by Lisa Owens Viani, author of "Sausal Creek Watershed, a Cultural and Natural History."

According to legend, the tree received its name from Dennis Dimond, son of Irish gold prospector and San Franciscan Hugh Dimond, who purchased 267 acres of land along Sausal Creek in 1867.

Dennis Dimond and his friends used to sneak bottles of champagne from Hugh Dimond's wine cellar and celebrated on the banks of Sausal Creek. On one occasion, when the boys spotted the housekeeper looking for them, they hid a bottle in a hollow of the tree. Supposedly the bottle was never retrieved. The city of Oakland purchased the Dimond property in 1917.

"In order to make the area safe, the tree needs to be removed," said Dan Gallagher, an arborist and supervisor for tree services in the Public Works Agency, who had planned to cut down the tree this week.

The tree is infected with brown rot fungus, indicating internal decay that could lead to limb breakage, Gallagher said. Its trunk is leaning and damaged with large openings caused by pruning and previous limb loss, he said.

"Typically, old trees do not have the ability to correct these defects by growing adaptive wood," Gallagher said. Though oaks in the wilderness have the capacity to live longer, he said, urban oaks may only live to 100 years old because of limited space for growth and environmental stress.

The oak is between 40 to 50 feet tall, its crown and limbs trimmed over the years to prolong its life, Gallagher said.

"Further reduction of the crown will compromise the tree's health and will not create a safer environment," he said.

Gallagher and his crew will inspect the tree from above next week, but he doesn't expect the results to change the conclusion of his ground-level inspection. He expects to remove the tree by Dec. 1.

The Friends of Sausal Creek has also hired an arborist to inspect the tree next week, said board member Mark Rauzon.

"The soul of Sausal Creek resides in this ancient oak," he said. "It saw the original residents of Sausal canyon come and go. Who knows? Maybe a grizzly bear sharpened his claws on the tree."

During his inspection, Gallagher said he will also determine the feasibility of replanting another oak in its place, but he doesn't recommend planting large oaks next to any building in areas with limited space. The last Dimond Park tree planting event occurred in 1998, when 10 oaks were planted during the Arbor Day celebration.

As the tree nears its farewell, Morgan plans to finish her ecology lessons this semester with goodbyes while looking for new tree stories.

"The next time you pass her," Rauzon said, "reflect a moment on this grand living being and wonder how much water has flowed down Sausal Creek since she was an acorn."