Pop stars and new fans flock to Central Park to savour Joni Mitchell's 1970s jazz period.

New York -- At the intimate outdoor SummerStage concert venue in Central Park, a U.S. flag stands stage right, watching over the events all summer long. Thursday night it was joined by one large Canadian flag, plus thousands of tiny ones fluttering in the audience, for a Canada Day concert billed as Joni's Jazz. Two dozen performers turned out for a celebration of Joni Mitchell's 1970s jazz period, including selections from the albums Court and Spark, Mingus, and The Hissing of Summer Lawns, and the entire 1974 Hejira.

Given the difficulty of the material and Mitchell's vocal idiosyncrasies that rightly scare away pretenders, the evening was a bold experiment that paid off frequently, if not always. Pop star Duncan Sheik's renditions of Court and Spark and Refuge of the Road were game attempts but mainly served to highlight his apparent lack of vocal training. Meanwhile, soul legend Chaka Khan, who had worked with Mitchell on 1977's Don Juan's Reckless Daughter, turned in three blistering, soulful covers. The overall effect wasn't so much a tribute to Mitchell as a rare opportunity to see her music pushed through new prisms: reconfigured, re-examined, and re-energized.

Backed by a lush assortment of 14 musicians and vocalists that included guitarist Vernon Reid (the evening's musical director), bassist Matthew Garrison, and Ravi Coltrane on saxophone, Toshi Reagan cracked open the show with a funked-up Trouble Child. Though she didn't show it, Reagan might have been slightly distracted because Mitchell herself -- who had not been expected to make the evening -- emerged from backstage during the song's opening bars to take a seat in front of the stage. The audience jumped to its feet, screaming for the guest of honour.

Reagan was followed by a fierce, meaty version of The Jungle Line by Dean Bowman and Carl Hancock Rux, heavy with cow bells, bongos and wild jungle calls. Mitchell practically danced in her seat, clearly thrilled at the version.

Jane Siberry took the stage for an uncertain People's Parties, which she later admitted "mortified" her because she had trouble reading the lyric sheet.

"I loved Joni Mitchell when I was young," Siberry said backstage. "She had a real awakening effect on me as a songwriter and musician because she spoke from her heart, which was not that common yet. There was a veil of courtesy and niceness that made the songs [before hers] less heartwarming. She moved a lot of people."

Siberry more than redeemed herself during the show's second half, bringing a coquettish, teasing intensity to her version of Hejira's Strange Boy, that she interpolated with occasional commentary (" 'Stiff blue-haired house rules' . . . nobody could write a line like that except Joni Mitchell").

Joe Jackson offered a yearning piano accompaniment to vocalist Joy Askew's moody take on Down to You with a brief sample of A Case of You thrown into the middle. Erin Hamilton (the daughter of Carol Burnett) brought a smoky nightclub read to Blue Motel Room, her voice kissing softly against a lone cornet. And rap singer PM Dawn brought in turntables for It's a Muggin'.

Backstage, Mitchell searched for the words to express her delight. "My intellect isn't with me yet, I'm all feeling right now," she said. "It's a rare occurrence for somebody to hear their music like this. It's delightful."

She went on to insist that she has always thought of herself as a Canadian, despite suggestions to the contrary that have dogged her through the years. "Please write that I'm an ambassador for Canada, I'm not an expatriate," she said.

The crowd, smaller than expected because of rain that let up only minutes before showtime, was obviously thrilled with their ambassador. "Joni Mitchell for PM!" yelled a few souls waving Canadian flags.

"It was beyond my expectations," said Corinne Aarsen, who was in from Edmonton visiting friends. Though previously unfamiliar with Mitchell's jazz period, Aarsen said the concert had changed that. "I'm a true fan now."

Her friend Michael Cromer, who moved to New York City a few years ago from Smithers, B.C., also declared himself "fully converted."

Mitchell has a younger posse coming along, too. "I got her autograph!" squealed 17-year-old Preeti Sodhi from New Jersey. "She's so awesome!"

Though Sodhi hasn't been a fan for long, she recently read about Mitchell's jazz period and thought it sounded interesting. "I was drawn by the fact that it wasn't very commercially successful. It's experimental, which is cool," she said.

Her friend Cory Fishman, 16, had been turned on to Mitchell a few years ago by an uncle. "I love her music because it's free and beautiful. It's just wonderful. She's wonderful!" said Fishman, waiting patiently by the backstage entrance, hoping to snap a few shots of her idol.

To their delight and a standing ovation, Mitchell finally took the stage at the end of the 3½-hour love-in to accept a bouquet of flowers and scat along to a few bars of the encore Help Me. No poetic licence would be necessary to report that, by that moment, the Canadian flag on stage had come unfurled and wrapped itself around its U.S. counterpart.