Actress Daryl Hannah has been removed by police from a tree in a Los Angeles community garden, protesting against the site's planned demolition.
Police, some in riot gear, arrested other demonstrators opposed to the plan to build a warehouse on the site.
Hannah last month said supporters had raised $6m (£3.2m) of the $16m (£8.5m) needed to save the plot.
Some 350 people have grown flowers and vegetables there since 1992. Folk singer Joan Baez has also campaigned.
The landowner says the gardeners are squatting on land designated for warehouses and factories in the South Central area of the city.
More than 100 police officers arrived at the 14-acre site on Tuesday to enforce an eviction notice.
The BBC's Peter Bowes in Los Angeles said several scuffles broke out and more than a dozen people were arrested.
Seventeen arrests were made inside the garden, sheriff's spokeswoman Kerri Webb said with a further 27 people demonstrating outside also arrested.
Other celebrities to have joined the campaign include Willie Nelson, Danny Glover and Laura Dern.
"I'm very confident this is the morally right thing to do, to take a principled stand in solidarity with the farmers," Hannah told the Associated Press by mobile phone before she was removed from the tree.
Officials brought in a fire truck to remove protestors
Inside the garden, firefighters had to cut free protesters who had chained themselves to the walnut tree, barrels filled with concrete and a picnic table.
Landowner Ralph Horowitz said that the farmers were squatting on land zoned for warehouses and factories.
In a telephone interview he said that he was paying $25,000 (£13,500) to $30,000 (£16,200) a month in mortgage and other land costs.
"We've made, in the last three years, enough of a donation to those farmers," he said. "I just want my land back."
He added: "I feel that the gardeners have been on the land for 14 years, almost 15 years for free. After 15 years, you say thank you."
Mr Horowitz also said that the city had provided other locations for the gardeners, and that most had left.
Mayor Antonio Villaraigosa called the evictions "unfortunate, disheartening".
He expressed frustrationthat a deal could not be reached despite months of negotiation and lamented the potential loss of "an oasis in a sea of industry and concrete".